COLORED GLASS SKULL BOTTLE SET 8 colorful skulls Halloween decor cork container Momentum

COLORED GLASS SKULL BOTTLE SET 8 colorful skulls Halloween decor cork container  Momentum
COLORED GLASS SKULL BOTTLE SET 8 colorful skulls Halloween decor cork container  Momentum - фотография #2
COLORED GLASS SKULL BOTTLE SET 8 colorful skulls Halloween decor cork container  Momentum - фотография #3
COLORED GLASS SKULL BOTTLE SET 8 colorful skulls Halloween decor cork container  Momentum - фотография #4
COLORED GLASS SKULL BOTTLE SET 8 colorful skulls Halloween decor cork container  Momentum - фотография #5
Бренд: Momentum
~ 4 891 ₽ 65.97 $

Характеристики

Country/Region of Manufacture China
Occasion Halloween
Time Period Manufactured Current (1991-Now)
Check out my other new & used items>>>>>>HERE! (click me)

FOR SALE:
A colorful set of Halloween-themed, glass containers
SET OF 8 COLORED GLASS SKULL BOTTLES WITH CORK

DETAILS:
These hauntingly cool bottles are sure to thrill fans of the macabre!
This 8-piece set of glass bottles features a wonderfully morbid skull shape and colors that will brighten any day. Each bottle has a short pour neck and a cork (or bung) stopper for its closure. You get two of each color: 2 ice blue, 2 electric purple, 2 blood red, 2 iridescent salmon. We believe the skulls are clear glass but they have their exterior colored. Decorate your colorful house of horrors during Halloween, or all-year-round, with some lovely glass skulls! 

Holds 12.85oz (380ml) of fluid!

Many Uses!
-They make great looking flower vases.
-Use to organize small items like buttons, beads and other small craft supplies.
-Make very cool night lights by fitting the holes with a bulb or using small battery-powered lights.
-Make 'em candle holders! Just uncork and put a candle stick in each - they'll look awesomely eerie when the wax runs.
-Surprise a friend with a sweet treat and reusable bottle - just fill with small candies!

Dimensions:
Height (with cork in): approx. 5-1/4"
Height (without cork): approx. 5"
Depth: approx. 4-1/2"
Width: approx. 3-1/2"

CONDITION:
In good, pre-owned condition. These bottles look great and have only minimal wear. Please see photos.
To ensure safe delivery, all items are carefully packaged before shipping out. 

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*ALL PHOTOS AND TEXT ARE INTELLECTUAL PROPERTY OF SIDEWAYS STAIRS CO. ALL RIGHTS RESERVED.*








































"Halloween or Hallowe'en (a contraction of Hallows' Even or Hallows' Evening),[5] also known as Allhalloween,[6] All Hallows' Eve,[7] or All Saints' Eve,[8] is a celebration observed in many countries on 31 October, the eve of the Western Christian feast of All Hallows' Day. It begins the three-day observance of Allhallowtide,[9] the time in the liturgical year dedicated to remembering the dead, including saints (hallows), martyrs, and all the faithful departed.[10][11]

It is widely believed that many Halloween traditions originated from ancient Celtic harvest festivals, particularly the Gaelic festival Samhain; that such festivals may have had pagan roots; and that Samhain itself was Christianized as Halloween by the early Church.[12][13][14][15][16] Some believe, however, that Halloween began solely as a Christian holiday, separate from ancient festivals like Samhain.[17][18][19][20]

Halloween activities include trick-or-treating (or the related guising and souling), attending Halloween costume parties, carving pumpkins into jack-o'-lanterns, lighting bonfires, apple bobbing, divination games, playing pranks, visiting haunted attractions, telling scary stories, as well as watching horror films.[21] In many parts of the world, the Christian religious observances of All Hallows' Eve, including attending church services and lighting candles on the graves of the dead, remain popular,[22][23][24] although elsewhere it is a more commercial and secular celebration.[25][26][27] Some Christians historically abstained from meat on All Hallows' Eve, a tradition reflected in the eating of certain vegetarian foods on this vigil day, including apples, potato pancakes, and soul cakes....

Etymology

The word appears as the title of Robert Burns' "Halloween" (1785), a poem traditionally recited by Scots
The word Halloween or Hallowe'en dates to about 1745[32] and is of Christian origin.[33] The word "Hallowe'en" means "Saints' evening".[34] It comes from a Scottish term for All Hallows' Eve (the evening before All Hallows' Day).[35] In Scots, the word "eve" is even, and this is contracted to e'en or een. Over time, (All) Hallow(s) E(v)en evolved into Hallowe'en. Although the phrase "All Hallows'" is found in Old English "All Hallows' Eve" is itself not seen until 1556.[35][36]

History
Gaelic and other Celtic influence

An early 20th-century Irish Halloween mask displayed at the Museum of Country Life.
Today's Halloween customs are thought to have been influenced by folk customs and beliefs from the Celtic-speaking countries, some of which are believed to have pagan roots.[37] Jack Santino, a folklorist, writes that "there was throughout Ireland an uneasy truce existing between customs and beliefs associated with Christianity and those associated with religions that were Irish before Christianity arrived".[38] Historian Nicholas Rogers, exploring the origins of Halloween, notes that while "some folklorists have detected its origins in the Roman feast of Pomona, the goddess of fruits and seeds, or in the festival of the dead called Parentalia, it is more typically linked to the Celtic festival of Samhain, which comes from the Old Irish for 'summer's end'."[39]

Samhain (/ˈsɑːwɪn, ˈsaʊɪn/) was the first and most important of the four quarter days in the medieval Gaelic calendar and was celebrated on 31 October – 1 November[40] in Ireland, Scotland and the Isle of Man.[41][42] A kindred festival was held at the same time of year by the Brittonic Celts, called Calan Gaeaf in Wales, Kalan Gwav in Cornwall and Kalan Goañv in Brittany; a name meaning "first day of winter". For the Celts, the day ended and began at sunset; thus the festival began on the evening before 7 November by modern reckoning (the half point between equinox and solstice).[43] Samhain and Calan Gaeaf are mentioned in some of the earliest Irish and Welsh literature. The names have been used by historians to refer to Celtic Halloween customs up until the 19th century,[44] and are still the Gaelic and Welsh names for Halloween.


Snap-Apple Night, painted by Daniel Maclise in 1833, shows people feasting and playing divination games on Halloween in Ireland.
Samhain/Calan Gaeaf marked the end of the harvest season and beginning of winter or the 'darker half' of the year.[45][46] Like Beltane/Calan Mai, it was seen as a liminal time, when the boundary between this world and the Otherworld thinned. This meant the Aos Sí (Connacht pronunciation /iːsˈʃiː/ eess-SHEE, Munster /e:s ʃi:/), the 'spirits' or 'fairies', could more easily come into this world and were particularly active.[47][48] Most scholars see the Aos Sí as "degraded versions of ancient gods [...] whose power remained active in the people's minds even after they had been officially replaced by later religious beliefs".[49] The Aos Sí were both respected and feared, with individuals often invoking the protection of God when approaching their dwellings.[50][51] At Samhain, it was believed that the Aos Sí needed to be propitiated to ensure that the people and their livestock survived the winter. Offerings of food and drink, or portions of the crops, were left outside for the Aos Sí.[52][53][54] The souls of the dead were also said to revisit their homes seeking hospitality.[55] Places were set at the dinner table and by the fire to welcome them.[56] The belief that the souls of the dead return home on one night of the year and must be appeased seems to have ancient origins and is found in many cultures throughout the world.[57] In 19th century Ireland, "candles would be lit and prayers formally offered for the souls of the dead. After this the eating, drinking, and games would begin".[58]

Throughout Ireland and Britain, the household festivities included rituals and games intended to foretell one's future, especially regarding death and marriage.[59] Apples and nuts were often used in these divination rituals. They included apple bobbing, nut roasting, scrying or mirror-gazing, pouring molten lead or egg whites into water, dream interpretation, and others.[60] Special bonfires were lit and there were rituals involving them. Their flames, smoke and ashes were deemed to have protective and cleansing powers, and were also used for divination.[45] In some places, torches lit from the bonfire were carried sunwise around homes and fields to protect them.[44] It is suggested that the fires were a kind of imitative or sympathetic magic – they mimicked the Sun, helping the "powers of growth" and holding back the decay and darkness of winter.[56][61][62] In Scotland, these bonfires and divination games were banned by the church elders in some parishes.[63] In Wales, bonfires were lit to "prevent the souls of the dead from falling to earth".[64] Later, these bonfires served to keep "away the devil".[65]

photograph
A traditional Irish Halloween turnip (rutabaga) lantern on display in the Museum of Country Life, Ireland
From at least the 16th century,[66] the festival included mumming and guising in Ireland, Scotland, the Isle of Man and Wales.[67] This involved people going house-to-house in costume (or in disguise), usually reciting verses or songs in exchange for food. It may have originally been a tradition whereby people impersonated the Aos Sí, or the souls of the dead, and received offerings on their behalf, similar to the custom of souling (see below). Impersonating these beings, or wearing a disguise, was also believed to protect oneself from them.[68] It is suggested that the mummers and guisers "personify the old spirits of the winter, who demanded reward in exchange for good fortune".[69] In parts of southern Ireland, the guisers included a hobby horse. A man dressed as a Láir Bhán (white mare) led youths house-to-house reciting verses – some of which had pagan overtones – in exchange for food. If the household donated food it could expect good fortune from the 'Muck Olla'; not doing so would bring misfortune.[70] In Scotland, youths went house-to-house with masked, painted or blackened faces, often threatening to do mischief if they were not welcomed.[67] F. Marian McNeill suggests the ancient festival included people in costume representing the spirits, and that faces were marked (or blackened) with ashes taken from the sacred bonfire.[66] In parts of Wales, men went about dressed as fearsome beings called gwrachod.[67] In the late 19th and early 20th century, young people in Glamorgan and Orkney cross-dressed.[67]

Elsewhere in Europe, mumming and hobby horses were part of other yearly festivals. However, in the Celtic-speaking regions they were "particularly appropriate to a night upon which supernatural beings were said to be abroad and could be imitated or warded off by human wanderers".[67] From at least the 18th century, "imitating malignant spirits" led to playing pranks in Ireland and the Scottish Highlands. Wearing costumes and playing pranks at Halloween spread to England in the 20th century.[67] Traditionally, pranksters used hollowed out turnips or mangel wurzels often carved with grotesque faces as lanterns.[67] By those who made them, the lanterns were variously said to represent the spirits,[67] or were used to ward off evil spirits.[71][72] They were common in parts of Ireland and the Scottish Highlands in the 19th century,[67] as well as in Somerset (see Punkie Night). In the 20th century they spread to other parts of England and became generally known as jack-o'-lanterns.[67]

Christian influence
Today's Halloween customs are thought to have been influenced by Christian dogma and practices derived from it.[73] Halloween is the evening before the Christian holy days of All Hallows' Day (also known as All Saints' or Hallowmas) on 1 November and All Souls' Day on 2 November, thus giving the holiday on 31 October the full name of All Hallows' Eve (meaning the evening before All Hallows' Day).[74] Since the time of the early Church,[75] major feasts in Christianity (such as Christmas, Easter and Pentecost) had vigils that began the night before, as did the feast of All Hallows'.[76] These three days are collectively called Allhallowtide and are a time for honoring the saints and praying for the recently departed souls who have yet to reach Heaven. Commemorations of all saints and martyrs were held by several churches on various dates, mostly in springtime.[77] In 609, Pope Boniface IV re-dedicated the Pantheon in Rome to "St Mary and all martyrs" on 13 May. This was the same date as Lemuria, an ancient Roman festival of the dead, and the same date as the commemoration of all saints in Edessa in the time of Ephrem.[78]

The feast of All Hallows', on its current date in the Western Church, may be traced to Pope Gregory III's (731–741) founding of an oratory in St Peter's for the relics "of the holy apostles and of all saints, martyrs and confessors".[79][80] In 835, All Hallows' Day was officially switched to 1 November, the same date as Samhain, at the behest of Pope Gregory IV.[81] Some suggest this was due to Celtic influence, while others suggest it was a Germanic idea,[81] although it is claimed that both Germanic and Celtic-speaking peoples commemorated the dead at the beginning of winter.[82] They may have seen it as the most fitting time to do so, as it is a time of 'dying' in nature.[81][82] It is also suggested that the change was made on the "practical grounds that Rome in summer could not accommodate the great number of pilgrims who flocked to it", and perhaps because of public health considerations regarding Roman Fever – a disease that claimed a number of lives during the sultry summers of the region.[83]



On All Hallows' Eve, Christians in some parts of the world visit cemeteries to pray and place flowers and candles on the graves of their loved ones.[84] The top photograph shows Bangladeshi Christians lighting candles on the headstone of a relative, while the bottom photograph shows Lutheran Christians praying and lighting candles in front of the central crucifix of a graveyard.
By the end of the 12th century they had become holy days of obligation across Europe and involved such traditions as ringing church bells for the souls in purgatory. In addition, "it was customary for criers dressed in black to parade the streets, ringing a bell of mournful sound and calling on all good Christians to remember the poor souls."[85] "Souling", the custom of baking and sharing soul cakes for all christened souls,[86] has been suggested as the origin of trick-or-treating.[87] The custom dates back at least as far as the 15th century[88] and was found in parts of England, Flanders, Germany and Austria.[57] Groups of poor people, often children, would go door-to-door during Allhallowtide, collecting soul cakes, in exchange for praying for the dead, especially the souls of the givers' friends and relatives.[88][89][90] Soul cakes would also be offered for the souls themselves to eat,[57] or the 'soulers' would act as their representatives.[91] As with the Lenten tradition of hot cross buns, Allhallowtide soul cakes were often marked with a cross, indicating that they were baked as alms.[92] Shakespeare mentions souling in his comedy The Two Gentlemen of Verona (1593).[93] On the custom of wearing costumes, Christian minister Prince Sorie Conteh wrote: "It was traditionally believed that the souls of the departed wandered the earth until All Saints' Day, and All Hallows' Eve provided one last chance for the dead to gain vengeance on their enemies before moving to the next world. In order to avoid being recognized by any soul that might be seeking such vengeance, people would don masks or costumes to disguise their identities".[94]

It is claimed that in the Middle Ages, churches that were too poor to display the relics of martyred saints at Allhallowtide let parishioners dress up as saints instead.[95][96] Some Christians continue to observe this custom at Halloween today.[97] Lesley Bannatyne believes this could have been a Christianization of an earlier pagan custom.[98] While souling, Christians would carry with them "lanterns made of hollowed-out turnips".[99] It has been suggested that the carved jack-o'-lantern, a popular symbol of Halloween, originally represented the souls of the dead.[100] On Halloween, in medieval Europe, fires served a dual purpose, being lit to guide returning souls to the homes of their families, as well as to deflect demons from haunting sincere Christian folk.[101][102] Households in Austria, England and Ireland often had "candles burning in every room to guide the souls back to visit their earthly homes". These were known as "soul lights".[103][104][105] Many Christians in mainland Europe, especially in France, believed "that once a year, on Hallowe'en, the dead of the churchyards rose for one wild, hideous carnival" known as the danse macabre, which has often been depicted in church decoration.[106] Christopher Allmand and Rosamond McKitterick write in The New Cambridge Medieval History that "Christians were moved by the sight of the Infant Jesus playing on his mother's knee; their hearts were touched by the Pietà; and patron saints reassured them by their presence. But, all the while, the danse macabre urged them not to forget the end of all earthly things."[107] This danse macabre was enacted at village pageants and at court masques, with people "dressing up as corpses from various strata of society", and may have been the origin of modern-day Halloween costume parties.[99][108][96][109]

In parts of Britain, these customs came under attack during the Reformation as some Protestants berated purgatory as a "popish" doctrine incompatible with their notion of predestination. Thus, for some Nonconformist Protestants, the theology of All Hallows' Eve was redefined; without the doctrine of purgatory, "the returning souls cannot be journeying from Purgatory on their way to Heaven, as Catholics frequently believe and assert. Instead, the so-called ghosts are thought to be in actuality evil spirits. As such they are threatening."[104] Other Protestants maintained belief in an intermediate state, known as Hades (Bosom of Abraham),[110] and continued to observe the original customs, especially souling, candlelit processions and the ringing of church bells in memory of the dead.[74][111] Mark Donnelly, a professor of medieval archaeology, and historian Daniel Diehl, with regard to the evil spirits, on Halloween, write that "barns and homes were blessed to protect people and livestock from the effect of witches, who were believed to accompany the malignant spirits as they traveled the earth."[112] In the 19th century, in some rural parts of England, families gathered on hills on the night of All Hallows' Eve. One held a bunch of burning straw on a pitchfork while the rest knelt around him in a circle, praying for the souls of relatives and friends until the flames went out. This was known as teen'lay.[113] Other customs included the tindle fires in Derbyshire and all-night vigil bonfires in Hertfordshire which were lit to pray for the departed.[114] The rising popularity of Guy Fawkes Night (5 November) from 1605 onward, saw many Halloween traditions appropriated by that holiday instead, and Halloween's popularity waned in Britain, with the noteworthy exception of Scotland.[115] There and in Ireland, they had been celebrating Samhain and Halloween since at least the early Middle Ages, and the Scottish kirk took a more pragmatic approach to Halloween, seeing it as important to the life cycle and rites of passage of communities and thus ensuring its survival in the country.[115]

In France, some Christian families, on the night of All Hallows' Eve, prayed beside the graves of their loved ones, setting down dishes full of milk for them.[103] On Halloween, in Italy, some families left a large meal out for ghosts of their passed relatives, before they departed for church services.[116] In Spain, on this night, special pastries are baked, known as "bones of the holy" (Spanish: Huesos de Santo) and put them on the graves of the churchyard, a practice that continues to this day.[117]

Spread to North America

The annual Greenwich Village Halloween Parade in Manhattan is the world's largest Halloween parade.
Lesley Bannatyne and Cindy Ott both wrote that Anglican colonists in the southern United States and Catholic colonists in Maryland "recognized All Hallow's Eve in their church calendars",[118][119] although the Puritans of New England maintained strong opposition to the holiday, along with other traditional celebrations of the established Church, including Christmas.[120] Almanacs of the late 18th and early 19th century give no indication that Halloween was widely celebrated in North America.[121] It was not until mass Irish and Scottish immigration in the 19th century that Halloween became a major holiday in North America.[121] Confined to the immigrant communities during the mid-19th century, it was gradually assimilated into mainstream society and by the first decade of the 20th century it was being celebrated coast to coast by people of all social, racial and religious backgrounds.[122] "In Cajun areas, a nocturnal Mass was said in cemeteries on Halloween night. Candles that had been blessed were placed on graves, and families sometimes spent the entire night at the graveside".[123] The yearly New York Halloween Parade, begun in 1974 by puppeteer and mask maker Ralph Lee of Greenwich Village, is the world's largest Halloween parade and America's only major nighttime parade, attracting more than 60,000 costumed participants, two million spectators, and a worldwide television audience of over 100 million.[124]

Symbols

At Halloween, yards, public spaces, and some houses may be decorated with traditionally macabre symbols including witches, skeletons, ghosts, cobwebs, and headstones.
Development of artifacts and symbols associated with Halloween formed over time. Jack-o'-lanterns are traditionally carried by guisers on All Hallows' Eve in order to frighten evil spirits.[100][125] There is a popular Irish Christian folktale associated with the jack-o'-lantern,[126] which in folklore is said to represent a "soul who has been denied entry into both heaven and hell":[127]

On route home after a night's drinking, Jack encounters the Devil and tricks him into climbing a tree. A quick-thinking Jack etches the sign of the cross into the bark, thus trapping the Devil. Jack strikes a bargain that Satan can never claim his soul. After a life of sin, drink, and mendacity, Jack is refused entry to heaven when he dies. Keeping his promise, the Devil refuses to let Jack into hell and throws a live coal straight from the fires of hell at him. It was a cold night, so Jack places the coal in a hollowed out turnip to stop it from going out, since which time Jack and his lantern have been roaming looking for a place to rest.[128]

In Ireland and Scotland, the turnip has traditionally been carved during Halloween,[129][130] but immigrants to North America used the native pumpkin, which is both much softer and much larger – making it easier to carve than a turnip.[129] The American tradition of carving pumpkins is recorded in 1837[131] and was originally associated with harvest time in general, not becoming specifically associated with Halloween until the mid-to-late 19th century.[132]


Decorated house in Weatherly, Pennsylvania
The modern imagery of Halloween comes from many sources, including Christian eschatology, national customs, works of Gothic and horror literature (such as the novels Frankenstein and Dracula) and classic horror films (such as Frankenstein and The Mummy).[133][134] Imagery of the skull, a reference to Golgotha in the Christian tradition, serves as "a reminder of death and the transitory quality of human life" and is consequently found in memento mori and vanitas compositions;[135] skulls have therefore been commonplace in Halloween, which touches on this theme.[136] Traditionally, the back walls of churches are "decorated with a depiction of the Last Judgment, complete with graves opening and the dead rising, with a heaven filled with angels and a hell filled with devils", a motif that has permeated the observance of this triduum.[137] One of the earliest works on the subject of Halloween is from Scottish poet John Mayne, who, in 1780, made note of pranks at Halloween; "What fearfu' pranks ensue!", as well as the supernatural associated with the night, "Bogies" (ghosts), influencing Robert Burns' "Halloween" (1785).[138] Elements of the autumn season, such as pumpkins, corn husks, and scarecrows, are also prevalent. Homes are often decorated with these types of symbols around Halloween. Halloween imagery includes themes of death, evil, and mythical monsters.[139] Black, orange, and sometimes purple are Halloween's traditional colors.

Trick-or-treating and guising
Main article: Trick-or-treating

Trick-or-treaters in Sweden
Trick-or-treating is a customary celebration for children on Halloween. Children go in costume from house to house, asking for treats such as candy or sometimes money, with the question, "Trick or treat?" The word "trick" implies a "threat" to perform mischief on the homeowners or their property if no treat is given.[87] The practice is said to have roots in the medieval practice of mumming, which is closely related to souling.[140] John Pymm wrote that "many of the feast days associated with the presentation of mumming plays were celebrated by the Christian Church."[141] These feast days included All Hallows' Eve, Christmas, Twelfth Night and Shrove Tuesday.[142][143] Mumming practiced in Germany, Scandinavia and other parts of Europe,[144] involved masked persons in fancy dress who "paraded the streets and entered houses to dance or play dice in silence".[145]


Girl in a Halloween costume in 1928, Ontario, Canada, the same province where the Scottish Halloween custom of guising is first recorded in North America
In England, from the medieval period,[146] up until the 1930s,[147] people practiced the Christian custom of souling on Halloween, which involved groups of soulers, both Protestant and Catholic,[111] going from parish to parish, begging the rich for soul cakes, in exchange for praying for the souls of the givers and their friends.[89] In the Philippines, the practice of souling is called Pangangaluwa and is practiced on All Hallow's Eve among children in rural areas.[21] People drape themselves in white cloths to represent souls and then visit houses, where they sing in return for prayers and sweets.[21]

In Scotland and Ireland, guising – children disguised in costume going from door to door for food or coins  – is a traditional Halloween custom, and is recorded in Scotland at Halloween in 1895 where masqueraders in disguise carrying lanterns made out of scooped out turnips, visit homes to be rewarded with cakes, fruit, and money.[130][148] The practice of guising at Halloween in North America is first recorded in 1911, where a newspaper in Kingston, Ontario, Canada reported children going "guising" around the neighborhood.[149]

American historian and author Ruth Edna Kelley of Massachusetts wrote the first book-length history of Halloween in the US; The Book of Hallowe'en (1919), and references souling in the chapter "Hallowe'en in America".[150] In her book, Kelley touches on customs that arrived from across the Atlantic; "Americans have fostered them, and are making this an occasion something like what it must have been in its best days overseas. All Halloween customs in the United States are borrowed directly or adapted from those of other countries".[151]

While the first reference to "guising" in North America occurs in 1911, another reference to ritual begging on Halloween appears, place unknown, in 1915, with a third reference in Chicago in 1920.[152] The earliest known use in print of the term "trick or treat" appears in 1927, in the Blackie Herald Alberta, Canada.[153]


An automobile trunk at a trunk-or-treat event at St. John Lutheran Church and Early Learning Center in Darien, Illinois
The thousands of Halloween postcards produced between the turn of the 20th century and the 1920s commonly show children but not trick-or-treating.[154] Trick-or-treating does not seem to have become a widespread practice until the 1930s, with the first US appearances of the term in 1934,[155] and the first use in a national publication occurring in 1939.[156]

A popular variant of trick-or-treating, known as trunk-or-treating (or Halloween tailgating), occurs when "children are offered treats from the trunks of cars parked in a church parking lot", or sometimes, a school parking lot.[117][157] In a trunk-or-treat event, the trunk (boot) of each automobile is decorated with a certain theme,[158] such as those of children's literature, movies, scripture, and job roles.[159] Trunk-or-treating has grown in popularity due to its perception as being more safe than going door to door, a point that resonates well with parents, as well as the fact that it "solves the rural conundrum in which homes [are] built a half-mile apart".[160][161]

Costumes
Main article: Halloween costume
Halloween costumes are traditionally modeled after supernatural figures such as vampires, monsters, ghosts, skeletons, witches, and devils.[87] Over time, the costume selection extended to include popular characters from fiction, celebrities, and generic archetypes such as ninjas and princesses.


Halloween shop in Derry, Northern Ireland selling masks
Dressing up in costumes and going "guising" was prevalent in Scotland and Ireland at Halloween by the late 19th century.[130] A Scottish term, the tradition is called "guising" because of the disguises or costumes worn by the children.[148] In Ireland the masks are known as 'false faces'.[162] Costuming became popular for Halloween parties in the US in the early 20th century, as often for adults as for children, and when trick-or-treating was becoming popular in Canada and the US in the 1920s and 1930s.[153][163]

Eddie J. Smith, in his book Halloween, Hallowed is Thy Name, offers a religious perspective to the wearing of costumes on All Hallows' Eve, suggesting that by dressing up as creatures "who at one time caused us to fear and tremble", people are able to poke fun at Satan "whose kingdom has been plundered by our Saviour". Images of skeletons and the dead are traditional decorations used as memento mori.[164][165]

"Trick-or-Treat for UNICEF" is a fundraising program to support UNICEF,[87] a United Nations Programme that provides humanitarian aid to children in developing countries. Started as a local event in a Northeast Philadelphia neighborhood in 1950 and expanded nationally in 1952, the program involves the distribution of small boxes by schools (or in modern times, corporate sponsors like Hallmark, at their licensed stores) to trick-or-treaters, in which they can solicit small-change donations from the houses they visit. It is estimated that children have collected more than $118 million for UNICEF since its inception. In Canada, in 2006, UNICEF decided to discontinue their Halloween collection boxes, citing safety and administrative concerns; after consultation with schools, they instead redesigned the program.[166][167]

Pet costumes
According to a 2018 report from the National Retail Federation, 30 million Americans will spend an estimated $480 million on Halloween costumes for their pets in 2018. This is up from an estimated $200 million in 2010. The most popular costumes for pets are the pumpkin, followed by the hot dog, and the bumble bee in third place.[168]

Games and other activities

In this 1904 Halloween greeting card, divination is depicted: the young woman looking into a mirror in a darkened room hopes to catch a glimpse of her future husband.
There are several games traditionally associated with Halloween. Some of these games originated as divination rituals or ways of foretelling one's future, especially regarding death, marriage and children. During the Middle Ages, these rituals were done by a "rare few" in rural communities as they were considered to be "deadly serious" practices.[169] In recent centuries, these divination games have been "a common feature of the household festivities" in Ireland and Britain.[59] They often involve apples and hazelnuts. In Celtic mythology, apples were strongly associated with the Otherworld and immortality, while hazelnuts were associated with divine wisdom.[170] Some also suggest that they derive from Roman practices in celebration of Pomona.[87]


Children bobbing for apples at Hallowe'en
The following activities were a common feature of Halloween in Ireland and Britain during the 17th–20th centuries. Some have become more widespread and continue to be popular today. One common game is apple bobbing or dunking (which may be called "dooking" in Scotland)[171] in which apples float in a tub or a large basin of water and the participants must use only their teeth to remove an apple from the basin. A variant of dunking involves kneeling on a chair, holding a fork between the teeth and trying to drive the fork into an apple. Another common game involves hanging up treacle or syrup-coated scones by strings; these must be eaten without using hands while they remain attached to the string, an activity that inevitably leads to a sticky face. Another once-popular game involves hanging a small wooden rod from the ceiling at head height, with a lit candle on one end and an apple hanging from the other. The rod is spun round and everyone takes turns to try to catch the apple with their teeth.[172]


Image from the Book of Hallowe'en (1919) showing several Halloween activities, such as nut roasting
Several of the traditional activities from Ireland and Britain involve foretelling one's future partner or spouse. An apple would be peeled in one long strip, then the peel tossed over the shoulder. The peel is believed to land in the shape of the first letter of the future spouse's name.[173][174] Two hazelnuts would be roasted near a fire; one named for the person roasting them and the other for the person they desire. If the nuts jump away from the heat, it is a bad sign, but if the nuts roast quietly it foretells a good match.[175][176] A salty oatmeal bannock would be baked; the person would eat it in three bites and then go to bed in silence without anything to drink. This is said to result in a dream in which their future spouse offers them a drink to quench their thirst.[177] Unmarried women were told that if they sat in a darkened room and gazed into a mirror on Halloween night, the face of their future husband would appear in the mirror.[178] However, if they were destined to die before marriage, a skull would appear. The custom was widespread enough to be commemorated on greeting cards[179] from the late 19th century and early 20th century.

In Ireland and Scotland, items would be hidden in food – usually a cake, barmbrack, cranachan, champ or colcannon – and portions of it served out at random. A person's future would be foretold by the item they happened to find; for example, a ring meant marriage and a coin meant wealth.[180]

Up until the 19th century, the Halloween bonfires were also used for divination in parts of Scotland, Wales and Brittany. When the fire died down, a ring of stones would be laid in the ashes, one for each person. In the morning, if any stone was mislaid it was said that the person it represented would not live out the year.[44]

Telling ghost stories and watching horror films are common fixtures of Halloween parties. Episodes of television series and Halloween-themed specials (with the specials usually aimed at children) are commonly aired on or before Halloween, while new horror films are often released before Halloween to take advantage of the holiday.

Haunted attractions

Humorous tombstones in front of a house in California
File:US Utah Ogden 25th Street Halloween 2019.ogv
Humorous display window in Historic 25th Street, Ogden, Utah
Main article: Haunted attraction (simulated)
Haunted attractions are entertainment venues designed to thrill and scare patrons. Most attractions are seasonal Halloween businesses that may include haunted houses, corn mazes, and hayrides,[181] and the level of sophistication of the effects has risen as the industry has grown.

The first recorded purpose-built haunted attraction was the Orton and Spooner Ghost House, which opened in 1915 in Liphook, England. This attraction actually most closely resembles a carnival fun house, powered by steam.[182][183] The House still exists, in the Hollycombe Steam Collection.

It was during the 1930s, about the same time as trick-or-treating, that Halloween-themed haunted houses first began to appear in America. It was in the late 1950s that haunted houses as a major attraction began to appear, focusing first on California. Sponsored by the Children's Health Home Junior Auxiliary, the San Mateo Haunted House opened in 1957. The San Bernardino Assistance League Haunted House opened in 1958. Home haunts began appearing across the country during 1962 and 1963. In 1964, the San Manteo Haunted House opened, as well as the Children's Museum Haunted House in Indianapolis.[184]

The haunted house as an American cultural icon can be attributed to the opening of the Haunted Mansion in Disneyland on 12 August 1969.[185] Knott's Berry Farm began hosting its own Halloween night attraction, Knott's Scary Farm, which opened in 1973.[186] Evangelical Christians adopted a form of these attractions by opening one of the first "hell houses" in 1972.[187]

The first Halloween haunted house run by a nonprofit organization was produced in 1970 by the Sycamore-Deer Park Jaycees in Clifton, Ohio. It was cosponsored by WSAI, an AM radio station broadcasting out of Cincinnati, Ohio. It was last produced in 1982.[188] Other Jaycees followed suit with their own versions after the success of the Ohio house. The March of Dimes copyrighted a "Mini haunted house for the March of Dimes" in 1976 and began fundraising through their local chapters by conducting haunted houses soon after. Although they apparently quit supporting this type of event nationally sometime in the 1980s, some March of Dimes haunted houses have persisted until today.[189]

On the evening of 11 May 1984, in Jackson Township, New Jersey, the Haunted Castle (Six Flags Great Adventure) caught fire. As a result of the fire, eight teenagers perished.[190] The backlash to the tragedy was a tightening of regulations relating to safety, building codes and the frequency of inspections of attractions nationwide. The smaller venues, especially the nonprofit attractions, were unable to compete financially, and the better funded commercial enterprises filled the vacuum.[191][192] Facilities that were once able to avoid regulation because they were considered to be temporary installations now had to adhere to the stricter codes required of permanent attractions.[193][194][195]

In the late 1980s and early 1990s, theme parks entered the business seriously. Six Flags Fright Fest began in 1986 and Universal Studios Florida began Halloween Horror Nights in 1991. Knott's Scary Farm experienced a surge in attendance in the 1990s as a result of America's obsession with Halloween as a cultural event. Theme parks have played a major role in globalizing the holiday. Universal Studios Singapore and Universal Studios Japan both participate, while Disney now mounts Mickey's Not-So-Scary Halloween Party events at its parks in Paris, Hong Kong and Tokyo, as well as in the United States.[196] The theme park haunts are by far the largest, both in scale and attendance.[197]

Food

Pumpkins for sale during Halloween
On All Hallows' Eve, many Western Christian denominations encourage abstinence from meat, giving rise to a variety of vegetarian foods associated with this day.[198]


A candy apple
Because in the Northern Hemisphere Halloween comes in the wake of the yearly apple harvest, candy apples (known as toffee apples outside North America), caramel apples or taffy apples are common Halloween treats made by rolling whole apples in a sticky sugar syrup, sometimes followed by rolling them in nuts.

At one time, candy apples were commonly given to trick-or-treating children, but the practice rapidly waned in the wake of widespread rumors that some individuals were embedding items like pins and razor blades in the apples in the United States.[199] While there is evidence of such incidents,[200] relative to the degree of reporting of such cases, actual cases involving malicious acts are extremely rare and have never resulted in serious injury. Nonetheless, many parents assumed that such heinous practices were rampant because of the mass media. At the peak of the hysteria, some hospitals offered free X-rays of children's Halloween hauls in order to find evidence of tampering. Virtually all of the few known candy poisoning incidents involved parents who poisoned their own children's candy.[201]

One custom that persists in modern-day Ireland is the baking (or more often nowadays, the purchase) of a barmbrack (Irish: báirín breac), which is a light fruitcake, into which a plain ring, a coin, and other charms are placed before baking.[202] It is considered fortunate to be the lucky one who finds it.[202] It has also been said that those who get a ring will find their true love in the ensuing year. This is similar to the tradition of king cake at the festival of Epiphany.


A jack-o'-lantern Halloween cake with a witches hat
List of foods associated with Halloween:

Barmbrack (Ireland)
Bonfire toffee (Great Britain)
Candy apples/toffee apples (Great Britain and Ireland)
Candy apples, candy corn, candy pumpkins (North America)
Chocolate
Monkey nuts (peanuts in their shells) (Ireland and Scotland)
Caramel apples
Caramel corn
Colcannon (Ireland; see below)
Halloween cake
Sweets/candy
Novelty candy shaped like skulls, pumpkins, bats, worms, etc.
Roasted pumpkin seeds
Roasted sweet corn
Soul cakes
Pumpkin Pie
Christian religious observances

The Vigil of All Hallows' is being celebrated at an Episcopal Christian church on Hallowe'en.
On Hallowe'en (All Hallows' Eve), in Poland, believers were once taught to pray out loud as they walk through the forests in order that the souls of the dead might find comfort; in Spain, Christian priests in tiny villages toll their church bells in order to remind their congregants to remember the dead on All Hallows' Eve.[203] In Ireland, and among immigrants in Canada, a custom includes the Christian practice of abstinence, keeping All Hallows' Eve as a meat-free day, and serving pancakes or colcannon instead.[204] In Mexico children make an altar to invite the return of the spirits of dead children (angelitos).[205]

The Christian Church traditionally observed Hallowe'en through a vigil. Worshippers prepared themselves for feasting on the following All Saints' Day with prayers and fasting.[206] This church service is known as the Vigil of All Hallows or the Vigil of All Saints;[207][208] an initiative known as Night of Light seeks to further spread the Vigil of All Hallows throughout Christendom.[209][210] After the service, "suitable festivities and entertainments" often follow, as well as a visit to the graveyard or cemetery, where flowers and candles are often placed in preparation for All Hallows' Day.[211][212] In Finland, because so many people visit the cemeteries on All Hallows' Eve to light votive candles there, they "are known as valomeri, or seas of light".[213]


Halloween Scripture Candy with gospel tract
Today, Christian attitudes towards Halloween are diverse. In the Anglican Church, some dioceses have chosen to emphasize the Christian traditions associated with All Hallow's Eve.[214][215] Some of these practices include praying, fasting and attending worship services.[1][2][3]

O LORD our God, increase, we pray thee, and multiply upon us the gifts of thy grace: that we, who do prevent the glorious festival of all thy Saints, may of thee be enabled joyfully to follow them in all virtuous and godly living. Through Jesus Christ, Our Lord, who liveth and reigneth with thee, in the unity of the Holy Ghost, ever one God, world without end. Amen. —Collect of the Vigil of All Saints, The Anglican Breviary[216]


Votive candles in the Halloween section of Walmart
Other Protestant Christians also celebrate All Hallows' Eve as Reformation Day, a day to remember the Protestant Reformation, alongside All Hallow's Eve or independently from it.[217] This is because Martin Luther is said to have nailed his Ninety-five Theses to All Saints' Church in Wittenberg on All Hallows' Eve.[218] Often, "Harvest Festivals" or "Reformation Festivals" are held on All Hallows' Eve, in which children dress up as Bible characters or Reformers.[219] In addition to distributing candy to children who are trick-or-treating on Hallowe'en, many Christians also provide gospel tracts to them. One organization, the American Tract Society, stated that around 3 million gospel tracts are ordered from them alone for Hallowe'en celebrations.[220] Others order Halloween-themed Scripture Candy to pass out to children on this day.[221][222]


Belizean children dressed up as Biblical figures and Christian saints
Some Christians feel concerned about the modern celebration of Halloween because they feel it trivializes – or celebrates – paganism, the occult, or other practices and cultural phenomena deemed incompatible with their beliefs.[223] Father Gabriele Amorth, an exorcist in Rome, has said, "if English and American children like to dress up as witches and devils on one night of the year that is not a problem. If it is just a game, there is no harm in that."[224] In more recent years, the Roman Catholic Archdiocese of Boston has organized a "Saint Fest" on Halloween.[225] Similarly, many contemporary Protestant churches view Halloween as a fun event for children, holding events in their churches where children and their parents can dress up, play games, and get candy for free. To these Christians, Halloween holds no threat to the spiritual lives of children: being taught about death and mortality, and the ways of the Celtic ancestors actually being a valuable life lesson and a part of many of their parishioners' heritage.[226] Christian minister Sam Portaro wrote that Halloween is about using "humor and ridicule to confront the power of death".[227]

In the Roman Catholic Church, Halloween's Christian connection is acknowledged, and Halloween celebrations are common in many Catholic parochial schools.[228][229] Many fundamentalist and evangelical churches use "Hell houses" and comic-style tracts in order to make use of Halloween's popularity as an opportunity for evangelism.[230] Others consider Halloween to be completely incompatible with the Christian faith due to its putative origins in the Festival of the Dead celebration.[231] Indeed, even though Eastern Orthodox Christians observe All Hallows' Day on the First Sunday after Pentecost, The Eastern Orthodox Church recommends the observance of Vespers or a Paraklesis on the Western observance of All Hallows' Eve, out of the pastoral need to provide an alternative to popular celebrations.[232]

Analogous celebrations and perspectives
Judaism
According to Alfred J. Kolatch in the Second Jewish Book of Why, in Judaism, Halloween is not permitted by Jewish Halakha because it violates Leviticus 18:3, which forbids Jews from partaking in gentile customs. Many Jews observe Yizkor communally four times a year, which is vaguely similar to the observance of Allhallowtide in Christianity, in the sense that prayers are said for both "martyrs and for one's own family".[233] Nevertheless, many American Jews celebrate Halloween, disconnected from its Christian origins.[234] Reform Rabbi Jeffrey Goldwasser has said that "There is no religious reason why contemporary Jews should not celebrate Halloween" while Orthodox Rabbi Michael Broyde has argued against Jews' observing the holiday.[235] Jews do have the holiday of Purim, where the children dress up in costumes to celebrate.[236]

Islam
Sheikh Idris Palmer, author of A Brief Illustrated Guide to Understanding Islam, has argued that Muslims should not participate in Halloween, stating that "participation in Halloween is worse than participation in Christmas, Easter, ... it is more sinful than congratulating the Christians for their prostration to the crucifix".[237] Javed Memon, a Muslim writer, has disagreed, saying that his "daughter dressing up like a British telephone booth will not destroy her faith as a Muslim".[238]

Hinduism
Hindus remember the dead during the festival of Pitru Paksha, during which Hindus pay homage to and perform a ceremony "to keep the souls of their ancestors at rest". It is celebrated in the Hindu month of Bhadrapada, usually in mid-September.[239] The celebration of the Hindu festival Diwali sometimes conflicts with the date of Halloween; but some Hindus choose to participate in the popular customs of Halloween.[240] Other Hindus, such as Soumya Dasgupta, have opposed the celebration on the grounds that Western holidays like Halloween have "begun to adversely affect our indigenous festivals".[241]

Neopaganism
There is no consistent rule or view on Halloween amongst those who describe themselves as Neopagans or Wiccans. Some Neopagans do not observe Halloween, but instead observe Samhain on 1 November,[242] some neopagans do enjoy Halloween festivities, stating that one can observe both "the solemnity of Samhain in addition to the fun of Halloween". Some neopagans are opposed to the celebration of Hallowe'en, stating that it "trivializes Samhain",[243] and "avoid Halloween, because of the interruptions from trick or treaters".[244] The Manitoban writes that "Wiccans don't officially celebrate Halloween, despite the fact that 31 Oct. will still have a star beside it in any good Wiccan's day planner. Starting at sundown, Wiccans celebrate a holiday known as Samhain. Samhain actually comes from old Celtic traditions and is not exclusive to Neopagan religions like Wicca. While the traditions of this holiday originate in Celtic countries, modern day Wiccans don't try to historically replicate Samhain celebrations. Some traditional Samhain rituals are still practised, but at its core, the period is treated as a time to celebrate darkness and the dead – a possible reason why Samhain can be confused with Halloween celebrations."[242]

Around the world
Main article: Geography of Halloween

Halloween display in Kobe, Japan
The traditions and importance of Halloween vary greatly among countries that observe it. In Scotland and Ireland, traditional Halloween customs include children dressing up in costume going "guising", holding parties, while other practices in Ireland include lighting bonfires, and having firework displays.[245][246] In Brittany children would play practical jokes by setting candles inside skulls in graveyards to frighten visitors.[247] Mass transatlantic immigration in the 19th century popularized Halloween in North America, and celebration in the United States and Canada has had a significant impact on how the event is observed in other nations. This larger North American influence, particularly in iconic and commercial elements, has extended to places such as Ecuador, Chile,[248] Australia,[249] New Zealand,[250] (most) continental Europe, Finland,[251] Japan, and other parts of East Asia.[252] In the Philippines, during Halloween, Filipinos return to their hometowns and purchase candles and flowers,[253] in preparation for the following All Saints Day (Araw ng mga Patay) on 1 November and All Souls Day – though it falls on 2 November, most of them observe it on the day before.[254] In Mexico and Latin America in general, it is referred to as " Día de Muertos " which translates in English to "Day of the dead". Most of the people from Latin America construct altars in their homes to honor their deceased relatives and they decorate them with flowers and candies and other offerings." (wikipedia.org)

"Glass coloring and color marking may be obtained by in several ways.

by the addition of coloring ions,[1][2]
by precipitation of nanometer sized colloides (so-called striking glasses[1] such as "gold ruby"[3] or red "selenium ruby"),[2]

Ancient Roman enamelled glass, 1st century, Begram Hoard
by colored inclusions (as in milk glass and smoked glass)
by light scattering (as in phase separated glass)[2]
by dichroic coatings (see dichroic glass), or
by colored coatings...

Coloring ions[edit]

Iron(II) oxide glass
Ordinary soda-lime glass appears colorless to the naked eye when it is thin, although iron oxide impurities produce a green tint which can be viewed in thick pieces or with the aid of scientific instruments. Further metals and metal oxides can be added to glass during its manufacture to change its color which can enhance its aesthetic appeal. Examples of these additives are listed below:


Amber Glass

Uranium glass glowing under UV light

Cobalt glass for decoration
Iron(II) oxide may be added to glass resulting in bluish-green glass which is frequently used in beer bottles. Together with chromium it gives a richer green color, used for wine bottles.
Sulfur, together with carbon and iron salts, is used to form iron polysulfides and produce amber glass ranging from yellowish to almost black. In borosilicate glasses rich in boron, sulfur imparts a blue color. With calcium it yields a deep yellow color.[4]
Manganese can be added in small amounts to remove the green tint given by iron, or in higher concentrations to give glass an amethyst color. Manganese is one of the oldest glass additives, and purple manganese glass was used since early Egyptian history.
Manganese dioxide, which is black, is used to remove the green color from the glass; in a very slow process this is converted to sodium permanganate, a dark purple compound. In New England some houses built more than 300 years ago have window glass which is lightly tinted violet because of this chemical change; and such glass panes are prized as antiques. This process is widely confused with the formation of "desert amethyst glass", in which glass exposed to desert sunshine with a high ultraviolet component develops a delicate violet tint. Details of the process and the composition of the glass vary and so do the results, because it is not a simple matter to obtain or produce properly controlled specimens.[5]
Small concentrations of cobalt (0.025 to 0.1%) yield blue glass. The best results are achieved when using glass containing potash. Very small amounts can be used for decolorizing.
2 to 3% of copper oxide produces a turquoise color.
Nickel, depending on the concentration, produces blue, or violet, or even black glass. Lead crystal with added nickel acquires purplish color. Nickel together with a small amount of cobalt was used for decolorizing of lead glass.
Chromium is a very powerful colorizing agent, yielding dark green[6] or in higher concentrations even black color. Together with tin oxide and arsenic it yields emerald green glass. Chromium aventurine, in which aventurescence was achieved by growth of large parallel chromium(III) oxide plates during cooling, was also made from glass with added chromium oxide in amount above its solubility limit in glass.
Cadmium together with sulphur forms cadmium sulfide and results in deep yellow color, often used in glazes. However, cadmium is toxic. Together with selenium and sulphur it yields shades of bright red and orange.[7]
Adding titanium produces yellowish-brown glass. Titanium, rarely used on its own, is more often employed to intensify and brighten other colorizing additives.
Uranium (0.1 to 2%) can be added to give glass a fluorescent yellow or green color.[8] Uranium glass is typically not radioactive enough to be dangerous, but if ground into a powder, such as by polishing with sandpaper, and inhaled, it can be carcinogenic. When used with lead glass with very high proportion of lead, produces a deep red color.
Didymium gives green color (used in UV filters) or lilac red.[7]
Striking glasses[edit]

Cranberry glass bowl

Photochromic eyeglass lens. The coloring is caused by silver nanoparticles.
Selenium, like manganese, can be used in small concentrations to decolorize glass, or in higher concentrations to impart a reddish color, caused by selenium nanoparticles dispersed in glass. It is a very important agent to make pink and red glass. When used together with cadmium sulfide,[9] it yields a brilliant red color known as "Selenium Ruby".
Pure metallic copper produces a very dark red, opaque glass, which is sometimes used as a substitute for gold in the production of ruby-colored glass.
Metallic gold, in very small concentrations (around 0.001%, or 10 ppm), produces a rich ruby-colored glass ("Ruby Gold" or "Rubino Oro"), while lower concentrations produces a less intense red, often marketed as "cranberry". The color is caused by the size and dispersion of gold particles. Ruby gold glass is usually made of lead glass with added tin.
Silver compounds such as silver nitrate and silver halides can produce a range of colors from orange-red to yellow. The way the glass is heated and cooled can significantly affect the colors produced by these compounds. Also photochromic lenses and photosensitive glass are based on silver.
Purple of Cassius is a purple pigment formed by the reaction of gold salts with tin(II) chloride.
Coloring added to glass[edit]
The principal methods of this are enamelled glass, essentially a technique for painting patterns or images, used for both glass vessels and on stained glass, and glass paint, typically in black, and silver stain, giving yellows to oranges on stained glass. All of these are fired in a kiln or furnace to fix them, and can be extremely durable when properly applied. This is not true of "cold-painted" glass, using oil paint or other mixtures, which rarely last more than a few centuries.

Colored inclusions[edit]
Tin oxide with antimony and arsenic oxides produce an opaque white glass (milk glass), first used in Venice to produce an imitation porcelain, very often then painted with enamels. Similarly, some smoked glasses may be based on dark-colored inclusions, but with ionic coloring it is also possible to produce dark colors (see above).

Color caused by scattering[edit]

The Tyndall effect in opalescent glass: it appears blue from the side, but orange light shines through.[10]

Porous glass pore-size gradient (large pores on the right); coloring based on the Tyndall effect.
Glass containing two or more phases with different refractive indices shows coloring based on the Tyndall effect and explained by the Mie theory, if the dimensions of the phases are similar or larger than the wavelength of visible light. The scattered light is blue and violet as seen in the image, while the transmitted light is yellow and red.

Dichroic glass[edit]
Main article: Dichroic glass

A pendant made from dichroic glass
Dichroic glass has one or several coatings in the nanometer-range (for example metals, metal oxides, or nitrides) which give the glass dichroic optical properties. Also the blue appearance of some automobile windshields is caused by dichroism." (wikipedia.org)

"Glass is a non-crystalline, often transparent amorphous solid, that has widespread practical, technological, and decorative use in, for example, window panes, tableware, and optics. Glass is most often formed by rapid cooling (quenching) of the molten form; some glasses such as volcanic glass are naturally occurring. The most familiar, and historically the oldest, types of manufactured glass are "silicate glasses" based on the chemical compound silica (silicon dioxide, or quartz), the primary constituent of sand. Soda-lime glass, containing around 70% silica, accounts for around 90% of manufactured glass. The term glass, in popular usage, is often used to refer only to this type of material, although silica-free glasses often have desirable properties for applications in modern communications technology. Some objects, such as drinking glasses and eyeglasses, are so commonly made of silicate-based glass that they are simply called by the name of the material.

Although brittle, silicate glass is extremely durable and many examples of glass fragments exist from early glass-making cultures. Archaeological evidence suggests glass-making dates back to at least 3,600 BCE in Mesopotamia, Egypt, or Syria. The earliest known glass objects were beads, perhaps created accidentally during metalworking or the production of faience. Due to its ease of formability into any shape, glass has been traditionally used for vessels, such as bowls, vases, bottles, jars and drinking glasses. In its most solid forms, it has also been used for paperweights and marbles. Glass can be coloured by adding metal salts or painted and printed with vitreous enamels, leading to its use in stained glass windows and other glass art objects.

The refractive, reflective and transmission properties of glass make glass suitable for manufacturing optical lenses, prisms, and optoelectronics materials. Extruded glass fibres have application as optical fibres in communications networks, thermal insulating material when matted as glass wool so as to trap air, or in glass-fibre reinforced plastic (fibreglass)....

History
Main article: History of glass

Roman cage cup from the 4th century CE
Naturally occurring obsidian glass was used by Stone Age societies as it fractures along very sharp edges, making it ideal for cutting tools and weapons.[20][21] Glassmaking dates back to at least 6000 years, long before humans had discovered how to smelt iron.[20] Archaeological evidence suggests that the first true synthetic glass was made in Lebanon and the coastal north Syria, Mesopotamia or ancient Egypt.[22][23] The earliest known glass objects, of the mid-third millennium BCE, were beads, perhaps initially created as accidental by-products of metalworking (slags) or during the production of faience, a pre-glass vitreous material made by a process similar to glazing.[24] Early glass was rarely transparent and often contained impurities and imperfections,[20] and is technically faience rather than true glass, which did not appear until 15th century BC.[25] However, red-orange glass beads excavated from the Indus Valley Civilization dated before 1700 BC (possibly as early as 1900 BC) predate sustained glass production, which appeared around 1600 in Mesopotamia and 1500 in Egypt.[26][27] During the Late Bronze Age there was a rapid growth in glassmaking technology in Egypt and Western Asia.[22] Archaeological finds from this period include coloured glass ingots, vessels, and beads.[22][28] Much early glass production relied on grinding techniques borrowed from stoneworking, such as grinding and carving glass in a cold state.[29]

The term glass developed in the late Roman Empire. It was in the Roman glassmaking centre at Trier (located in current-day Germany), that the late-Latin term glesum originated, probably from a Germanic word for a transparent, lustrous substance.[30] Glass objects have been recovered across the Roman Empire[31] in domestic, funerary,[32] and industrial contexts.[33] Examples of Roman glass have been found outside of the former Roman Empire in China,[34] the Baltics, the Middle East, and India.[35] The Romans perfected cameo glass, produced by etching and carving through fused layers of different colours to produce a design in relief on the glass object.[36]


Windows in the choir of the Basilica of Saint Denis, one of the earliest uses of extensive areas of glass (early 13th-century architecture with restored glass of the 19th century)
In post-classical West Africa, Benin was a manufacturer of glass and glass beads.[37] Glass was used extensively in Europe during the Middle Ages. Anglo-Saxon glass has been found across England during archaeological excavations of both settlement and cemetery sites.[38] From the 10th-century onwards, glass was employed in stained glass windows of churches and cathedrals, with famous examples at Chartres Cathedral and the Basilica of Saint Denis. By the 14th-century, architects were designing buildings with walls of stained glass such as Sainte-Chapelle, Paris, (1203–1248) and the East end of Gloucester Cathedral. With the change in architectural style during the Renaissance period in Europe, the use of large stained glass windows became much less prevalent,[39] although stained glass had a major revival with Gothic Revival architecture in the 19th century.[40]

During the 13th century, the island of Murano, Venice, became a centre for glass making, building on medieval techniques to produce colourful ornamental pieces in large quantities.[36] Murano glass makers developed the exceptionally clear colourless glass cristallo, so called for its resemblance to natural crystal, and extensively used for windows, mirrors, ships' lanterns, and lenses.[20] In the 13th, 14th, and 15th centuries, enamelling and gilding on glass vessels was perfected in Egypt and Syria.[41] Towards the end of the 17th century, Bohemia became an important region for glass production, remaining so until the start of the 20th century. By the 17th century, glass was also being produced in England in the Venetian tradition. In around 1675, George Ravenscroft invented lead crystal glass, with cut glass becoming fashionable in the 18th century.[36] Ornamental glass objects became an important art medium during the Art Nouveau period in the late 19th century.[36]

Throughout the 20th century, new mass production techniques led to the widespread availability and utility for bulk glass and its increased use as a building material and new applications of glass.[42] In the 1920s a mould-etch process was developed, in which art was etched directly into the mould, so that each cast piece emerged from the mould with the image already on the surface of the glass. This reduced manufacturing costs and, combined with a wider use of coloured glass, led to cheap glassware in the 1930s, which later became known as Depression glass.[43] In the 1950s, Pilkington Bros., England, developed the float glass process, producing high-quality distortion free flat sheets of glass by floating on molten tin.[20] Modern multi-story buildings are frequently constructed with curtain walls made almost entirely of glass.[44] Similarly, laminated glass has been widely applied to vehicles for windscreens.[45] Optical glass for spectacles has been used since the Middle Ages.[46] The production of lenses has become increasingly proficient, aiding astronomers[47] as well as having other application in medicine and science.[48] Glass is also employed as the aperture cover in many solar energy collectors.[49]

In the 21st century, glass manufacturers have developed different brands of chemically strengthened glass for widespread application in touchscreens for smartphones, tablet computers, and many other types of information appliances. These include Gorilla glass, developed and manufactured by Corning, AGC Inc.'s Dragontrail and Schott AG's Xensation....

Following the glass batch preparation and mixing, the raw materials are transported to the furnace. Soda-lime glass for mass production is melted in gas fired units. Smaller scale furnaces for specialty glasses include electric melters, pot furnaces, and day tanks.[71] After melting, homogenization and refining (removal of bubbles), the glass is formed. Flat glass for windows and similar applications is formed by the float glass process, developed between 1953 and 1957 by Sir Alastair Pilkington and Kenneth Bickerstaff of the UK's Pilkington Brothers, who created a continuous ribbon of glass using a molten tin bath on which the molten glass flows unhindered under the influence of gravity. The top surface of the glass is subjected to nitrogen under pressure to obtain a polished finish.[107] Container glass for common bottles and jars is formed by blowing and pressing methods.[108] This glass is often slightly modified chemically (with more alumina and calcium oxide) for greater water resistance.[109]


Glass blowing
Once the desired form is obtained, glass is usually annealed for the removal of stresses and to increase the glass's hardness and durability.[110] Surface treatments, coatings or lamination may follow to improve the chemical durability (glass container coatings, glass container internal treatment), strength (toughened glass, bulletproof glass, windshields[111]), or optical properties (insulated glazing, anti-reflective coating).[112]

New chemical glass compositions or new treatment techniques can be initially investigated in small-scale laboratory experiments. The raw materials for laboratory-scale glass melts are often different from those used in mass production because the cost factor has a low priority. In the laboratory mostly pure chemicals are used. Care must be taken that the raw materials have not reacted with moisture or other chemicals in the environment (such as alkali or alkaline earth metal oxides and hydroxides, or boron oxide), or that the impurities are quantified (loss on ignition).[113] Evaporation losses during glass melting should be considered during the selection of the raw materials, e.g., sodium selenite may be preferred over easily evaporating selenium dioxide (SeO2). Also, more readily reacting raw materials may be preferred over relatively inert ones, such as aluminum hydroxide (Al(OH)3) over alumina (Al2O3). Usually, the melts are carried out in platinum crucibles to reduce contamination from the crucible material. Glass homogeneity is achieved by homogenizing the raw materials mixture (glass batch), by stirring the melt, and by crushing and re-melting the first melt. The obtained glass is usually annealed to prevent breakage during processing.[113][114]

Colour
Main article: Glass coloring and color marking
Colour in glass may be obtained by addition of homogenously distributed electrically charged ions (or colour centres). While ordinary soda-lime glass appears colourless in thin section, iron(II) oxide (FeO) impurities produce a green tint in thick sections.[115] Manganese dioxide (MnO2), which gives glass a purple colour, may be added to remove the green tint given by FeO.[116] FeO and chromium(III) oxide (Cr2O3) additives are used in the production of green bottles.[115] Iron (III) oxide, on the other-hand, produces yellow or yellow-brown glass.[117] Low concentrations (0.025 to 0.1%) of cobalt oxide (CoO) produces rich, deep blue cobalt glass.[118] Chromium is a very powerful colourising agent, yielding dark green.[119] Sulphur combined with carbon and iron salts produces amber glass ranging from yellowish to almost black.[120] A glass melt can also acquire an amber colour from a reducing combustion atmosphere.[121] Cadmium sulfide produces imperial red, and combined with selenium can produce shades of yellow, orange, and red.[115][117] The additive Copper(II) oxide (CuO) produces a turquoise colour in glass, in contrast to Copper(I) oxide (Cu2O) which gives a dull brown-red colour.[122]


Iron(II) oxide and chromium(III) oxide additives are often used in the production of green bottles.[115]
 

Cobalt oxide produces rich, deep blue glass, such as Bristol blue glass.
 

Different oxide additives produce the different colours in glass: turquoise (Copper(II) oxide),[122] purple (Manganese dioxide),[115] and red (Cadmium sulfide).[115]
 

Red glass bottle with yellow glass overlay
 

Amber-coloured glass
 

Four-colour Roman glass bowl, manufactured circa 1st century B.C.
Uses

The Shard glass skyscraper, in London.
Architecture and windows
Main articles: Architectural glass and Window
Soda-lime sheet glass is typically used as transparent glazing material, typically as windows in external walls of buildings. Float or rolled sheet glass products is cut to size either by scoring and snapping the material, laser cutting, water jets, or diamond bladed saw. The glass may be thermally or chemically tempered (strengthened) for safety and bent or curved during heating. Surface coatings may be added for specific functions such as scratch resistance, blocking specific wavelengths of light (e.g. infrared or ultraviolet), dirt-repellence (e.g. self-cleaning glass), or switchable electrochromic coatings.[123]

Structural glazing systems represent one of the most significant architectural innovations of modern times, where glass buildings now often dominate skylines of many modern cities.[124] These systems use stainless steel fittings countersunk into recesses in the corners of the glass panels allowing strengthened panes to appear unsupported creating a flush exterior.[124] Structural glazing systems have their roots in iron and glass conservatories of the nineteenth century[125]

Tableware
Main articles: Tableware and List of glassware
Glass is an essential component of tableware and is typically used for water, beer and wine drinking glasses.[48] Wine glasses are typically stemware, i.e. goblets formed from a bowl, stem, and foot. Crystal or Lead crystal glass may be cut and polished to produce decorative drinking glasses with gleaming facets.[126][127] Other uses of glass in tableware include decanters, jugs, plates, and bowls.[48]

Wine glasses and other glass tableware
 

Dimpled glass beer pint jug
 

Cut lead crystal glass
 
A glass decanter and stopper
Packaging
Main article: Container glass
The inert and impermeable nature of glass makes it a stable and widely used material for food and drink packaging as glass bottles and jars. Most container glass is soda-lime glass, produced by blowing and pressing techniques. Container glass has a lower magnesium oxide and sodium oxide content than flat glass, and a higher Silica, Calcium oxide, and Aluminum oxide content.[128] Its higher content of water-insoluble oxides imparts slightly higher chemical durability against water, which is advantageous for storing beverages and food. Glass packaging is sustainable, readily recycled, reusable and refillable.[129]

For electronics applications, glass can be used as a substrate in the manufacture of integrated passive devices, thin-film bulk acoustic resonators, and as a hermetic sealing material in device packaging, [130][131] including very thin solely glass based encapsulation of integrated circuits and other semiconductors in high manufacturing volumes.[132]

Laboratories
Main article: Laboratory glassware
Glass is an important material in scientific laboratories for the manufacture of experimental apparatus because it is relatively cheap, readily formed into required shapes for experiment, easy to keep clean, can withstand heat and cold treatment, is generally non-reactive with many reagents, and its transparency allows for the observation of chemical reactions and processes.[133][134] Laboratory glassware applications include flasks, petri dishes, test tubes, pipettes, graduated cylinders, glass lined metallic containers for chemical processing, fractionation columns, glass pipes, Schlenk lines, gauges, and thermometers.[135][133] Although most standard laboratory glassware has been mass-produced since the 1920s, scientists still employ skilled glassblowers to manufacture bespoke glass apparatus for their experimental requirements.[136]

A Vigreux column in a laboratory setup
 

A Schlenk line with four ports
 

Graduated cylinders
 

Erlenmeyer flask
Optics
Glass is a ubiquitous material in optics by virtue of its ability to refract, reflect, and transmit light. These and other optical properties can be controlled by varying chemical compositions, thermal treatment, and manufacturing techniques. The many applications of glass in optics includes glasses for eyesight correction, imaging optics (e.g. lenses and mirrors in telescopes, microscopes, and cameras), fibre optics in telecommunications technology, and integrated optics. Microlenses and gradient-index optics (where the refractive index is non-uniform) find application in e.g. reading optical discs, laser printers, photocopiers, and laser diodes. [53]

Art
Main articles: Studio glass, Art glass, and Glass art
The 19th century saw a revival in ancient glass-making techniques including cameo glass, achieved for the first time since the Roman Empire, initially mostly for pieces in a neo-classical style. The Art Nouveau movement made great use of glass, with René Lalique, Émile Gallé, and Daum of Nancy in the first French wave of the movement, producing coloured vases and similar pieces, often in cameo glass or in luster techniques.[137] Louis Comfort Tiffany in America specialized in stained glass, both secular and religious, in panels and his famous lamps. The early 20th-century saw the large-scale factory production of glass art by firms such as Waterford and Lalique. Small studios may hand-produce glass artworks. Techniques for producing glass art include blowing, kiln-casting, fusing, slumping, pâte de verre, flame-working, hot-sculpting and cold-working. Cold work includes traditional stained glass work and other methods of shaping glass at room temperature. Objects made out of glass include vessels, paperweights, marbles, beads, sculptures and installation art." (wikipedia.org)

"A bottle is a narrow-necked container made of an impermeable material (clay, glass, plastic, aluminium etc.) in various shapes and sizes to store and transport liquids (water, milk, beer, wine, ink, cooking oil, medicine, soft drinks, shampoo, and chemicals, etc.) and whose mouth at the bottling line can be sealed with an internal stopper, an external bottle cap, a closure, or a conductive "inner seal" using induction sealing.[1] Some of the earliest bottles appeared in China, Phoenicia, Crete, and Rome....

Etymology[edit]
First attested in 14th century. From the English word bottle derives from an Old French word boteille, from vulgar Latin butticula, from late Latin buttis ("cask"), a latinisation of the Greek βοῦττις (bouttis) ("vessel").[2][3]

Types of bottle[edit]
Glass bottles[edit]
Main article: Glass bottle
Wine bottles[edit]
Main article: Wine bottle
The glass bottle represented an important development in the history of wine, because, when combined with a high-quality stopper such as a cork, it allowed long-term aging of wine. Glass has all the qualities required for long-term storage. It eventually gave rise to "château bottling", the practice where an estate's wine is put in a bottle at the source, rather than by a merchant. Prior to this, wine used to be sold by the barrel (and before that, the amphora) and put into bottles only at the merchant's shop, if at all. This left large and often abused opportunities for fraud and adulteration, as consumers had to trust the merchant as to the contents. It is thought that most wine consumed outside of wine-producing regions had been tampered with in some way. Also, not all merchants were careful to avoid oxidation or contamination while bottling, leading to large bottle variation. Particularly in the case of port, certain conscientious merchants' bottling of old ports fetch higher prices even today. To avoid these problems, most fine wine is bottled at the place of production (including all port, since 1974).

There are many sizes and shapes of bottles used for wine. Some of the known shapes:

"Bordeaux": This bottle is roughly straight sided with a curved "shoulder" that is useful for catching sediment and is also the easiest to stack. Traditionally used in Bordeaux but now worldwide, this is probably the most common type.
"Burgundy": Traditionally used in Burgundy, this has sides that taper down about 2/3 of the height to a short cylindrical section, and does not have a shoulder.
"Champagne": Traditionally used for Champagne, it is similar to a Burgundy bottle, but with a wider base. Also, it is heavier due to the pressurization.
Codd-neck bottles[edit]
Main article: Codd-neck bottle

Codd-neck bottle
In 1872, British soft drink makers Hiram Codd of Camberwell, London, designed and patented a bottle designed specifically for carbonated drinks. The Codd-neck bottle was designed and manufactured to enclose a marble and a rubber washer/gasket in the neck. The bottles were filled upside down, and pressure of the gas in the bottle forced the marble against the washer, sealing in the carbonation. The bottle was pinched into a special shape, as can be seen in the photo to the left, to provide a chamber into which the marble was pushed to open the bottle. This prevented the marble from blocking the neck as the drink was poured.

Soon after its introduction, the bottle became extremely popular with the soft drink and brewing industries, mainly in Europe, Asia and Australasia, though some alcohol drinkers disdained the use of the bottle. One etymology of the term codswallop originates from beer sold in Codd bottles, though this is generally dismissed as a folk etymology.[4]

The bottles were regularly produced for many decades, but gradually declined in usage. Since children smashed the bottles to retrieve the marbles, they are relatively scarce and have become collector items; particularly in the UK. A cobalt-coloured Codd bottle today fetches hundreds of British pounds at auction. The Codd-neck design is still used for the Japanese soft drink Ramune and in the Indian drink called Banta.[5]

Plastic bottles[edit]
Main article: Plastic bottle
[icon]
This section needs expansion. You can help by adding to it. (October 2015)
The plastic is strain oriented in the stretch blow molding manufacturing process. Plastic bottles are typically used to store liquids such as water, soft drinks, motor oil, cooking oil, medicine, shampoo, milk, and ink. The size ranges from very small sample bottles to very large carboys. The main advantage that plastic bottles have over glass is their superior resistance to breakage, in both production and transportation, as well as their low cost of production; however, their contribution towards plastic pollution is considerable.

Aluminium bottles[edit]
Main article: Aluminium bottle
An aluminium bottle is a bottle made of aluminium (or aluminum, in American English). In some countries, it is also referred to as a "bottlecan". It is a bottle made entirely of aluminium that holds beer, soft drinks, wine, and other liquids.

Hot water bottles[edit]
Main article: Hot water bottle
A hot water bottle is a bottle filled with hot water used to provide warmth. It can be made from various materials, most commonly rubber, but has historically been made from harder materials such as metal, glass, earthenware, or wood." (wikipedia.org)

"A bung, stopper or cork is a cylindrical or conical closure used to seal a container, such as a bottle, tube or barrel. Unlike a lid, which encloses a container from the outside without displacing the inner volume, a bung is partially or wholly inserted inside the container to act as a seal.

A bung can be defined as "a plug or closure used to close an opening in a drum or barrel. Called a plug when referring to a steel drum closure."[1]

A glass stopper is often called a "ground glass joint" (or "joint taper"), a rubber stopper is sometimes called a "rubber bung", and a cork stopper is called simply a "cork". Bung stoppers used for wine bottles are referred to as "corks", even when made from another material.

A common every-day example of a bung is the cork of a wine bottle. Bungs are used to seal the bunghole of barrels. Other bungs, particularly those used in chemical barrels, may be made of metal and be screwed into place via threading....

Ground glass joint[edit]
Main article: Ground glass joint

Ground glass stoppers
Ground glass joint (or ground glass stoppers) are commonly used with laboratory glassware, mainly because of their nonreactivity. Some stoppers used in labs have holes in them to allow the insertion of glass or rubber tubing. This is often used when a reaction is taking place in the flask or test tube and the byproduct or result of the reaction is desired to be collected. For instance, if one were to boil water in a test tube and wanted to collect the water vapor, one could seal the test tube with a stopper with holes in it. With tubing inserted into the hole(s), when the tube is heated, water vapor will rise through the hole, make its way through the tubing, and into the collection chamber of choice. The water vapor would not be able to escape into the air, because the stopper and the tubing, if set up correctly, would be airtight.

Rubber bungs[edit]
Cork stopper for wine bottle.
Cork stoppers from wine bottles.
Main article: Laboratory rubber stopper
In chemistry, bungs made of hardened rubber are frequently used in small-scale experimental set-ups involving non-corrosive gases. Some chemistry bungs may also include one or more holes so a glass tube or laboratory funnel may be inserted through the bung and into the container or another piece of apparatus. The rubber bung may be used to seal a flask because the user may require the contents to be mixed via shaking the flask or may require that the contents be kept inside the flask and prevented from leaking out. In all cases, the bung keeps the experimentation environment sealed so that liquids or gases cannot escape (or enter).

For applications that place higher demands on the bung in terms of temperature and mechanical stability or solvent resistance, standardized glass stoppers and connectors are preferred.

Bottle stoppers made from gutta-percha, a natural rubber that is both chemically resistant and thermoplastic, were the first product of the Gutta Percha Company, better known for making submarine telegraph cable.Ground glass joint[edit]
Main article: Ground glass joint

Ground glass stoppers
Ground glass joint (or ground glass stoppers) are commonly used with laboratory glassware, mainly because of their nonreactivity. Some stoppers used in labs have holes in them to allow the insertion of glass or rubber tubing. This is often used when a reaction is taking place in the flask or test tube and the byproduct or result of the reaction is desired to be collected. For instance, if one were to boil water in a test tube and wanted to collect the water vapor, one could seal the test tube with a stopper with holes in it. With tubing inserted into the hole(s), when the tube is heated, water vapor will rise through the hole, make its way through the tubing, and into the collection chamber of choice. The water vapor would not be able to escape into the air, because the stopper and the tubing, if set up correctly, would be airtight.

Rubber bungs[edit]
Cork stopper for wine bottle.
Cork stoppers from wine bottles.
Main article: Laboratory rubber stopper
In chemistry, bungs made of hardened rubber are frequently used in small-scale experimental set-ups involving non-corrosive gases. Some chemistry bungs may also include one or more holes so a glass tube or laboratory funnel may be inserted through the bung and into the container or another piece of apparatus. The rubber bung may be used to seal a flask because the user may require the contents to be mixed via shaking the flask or may require that the contents be kept inside the flask and prevented from leaking out. In all cases, the bung keeps the experimentation environment sealed so that liquids or gases cannot escape (or enter).

For applications that place higher demands on the bung in terms of temperature and mechanical stability or solvent resistance, standardized glass stoppers and connectors are preferred.

Bottle stoppers made from gutta-percha, a natural rubber that is both chemically resistant and thermoplastic, were the first product of the Gutta Percha Company, better known for making submarine telegraph cable." (wikipedia.org)

"A jar is a rigid, cylindrical or slightly conical container, typically made of glass, ceramic, or plastic, with a wide mouth or opening that can be closed with a lid, screw cap, lug cap, cork stopper, roll-on cap, crimp-on cap, press-on cap, plastic shrink, heat sealed lidding film, an inner seal, a Tamper-evident band, or other suitable means.


Some regions[In what country?] have a legally mandated deposit refundable upon return of the jar to its retailer, after which the jar is recycled according to the SPI recycling code for the material....

Etymology[edit]
The English word "jar" originates from the Arabic word jarra, which means an earthen pot or vessel.[2][3]

Creation[edit]
Jars are sterilised by putting them in a pressure cooker with boiling water or an oven for a number of minutes. Glass jars are considered microwavable.[4]

Utility[edit]
Jars can be used to hold solids too large to be removed from, or liquids too viscous to be poured through, a bottle's neck; these may be foods, cosmetics, medications, or chemicals. [5] Glass jars—among which the most popular is the mason jar—can be used for storing and preserving items as diverse as jam, pickled gherkin, other pickles, marmalade, sun-dried tomatoes, olives, jalapeño peppers, chutneys, pickled eggs, honey, and many others.

Types[edit]
Bell jar in a laboratory
Cookie jar
Killing jar, used to kill captured insects
Kilner jar, for food storage
Leyden jar, a historical capacitor
Mason jar, for food storage
Specimen jar, an instrument used in anatomy to preserve specimens" (wikipedia.org)

"The skull is a bony structure that forms the head in vertebrates. It supports the structures of the face and provides a protective cavity for the brain.[1] The skull is composed of two parts: the cranium and the mandible. In humans, these two parts are the neurocranium and the viscerocranium (facial skeleton) that includes the mandible as its largest bone. The skull forms the anterior-most portion of the skeleton and is a product of cephalisation—housing the brain, and several sensory structures such as the eyes, ears, nose, and mouth.[2] In humans these sensory structures are part of the facial skeleton.

Functions of the skull include protection of the brain, fixing the distance between the eyes to allow stereoscopic vision, and fixing the position of the ears to enable sound localisation of the direction and distance of sounds. In some animals, such as horned ungulates (mammals with hooves), the skull also has a defensive function by providing the mount (on the frontal bone) for the horns.

The English word "skull" is probably derived from Old Norse "skulle", while the Latin word cranium comes from the Greek root κρανίον (kranion).

The skull is made up of a number of fused flat bones, and contains many foramina, fossae, processes, and several cavities or sinuses. In zoology there are openings in the skull called fenestrae....

Structure[edit]
Humans[edit]
For details and the constituent bones, see Neurocranium and Facial skeleton.

Skull in situ

Anatomy of a flat bone - the periosteum of the neurocranium is known as the pericranium

Human skull from the front

Side bones of skull
The human skull is the bony structure that forms the head in the human skeleton. It supports the structures of the face and forms a cavity for the brain. Like the skulls of other vertebrates, it protects the brain from injury.[3]

The skull consists of three parts, of different embryological origin—the neurocranium, the sutures, and the facial skeleton (also called the membraneous viscerocranium). The neurocranium (or braincase) forms the protective cranial cavity that surrounds and houses the brain and brainstem.[4] The upper areas of the cranial bones form the calvaria (skullcap). The membranous viscerocranium includes the mandible.

The sutures are fairly rigid joints between bones of the neurocranium.

The facial skeleton is formed by the bones supporting the face.

Bones[edit]
Except for the mandible, all of the bones of the skull are joined together by sutures—synarthrodial (immovable) joints formed by bony ossification, with Sharpey's fibres permitting some flexibility. Sometimes there can be extra bone pieces within the suture known as wormian bones or sutural bones. Most commonly these are found in the course of the lambdoid suture.

The human skull is generally considered to consist of twenty-two bones—eight cranial bones and fourteen facial skeleton bones. In the neurocranium these are the occipital bone, two temporal bones, two parietal bones, the sphenoid, ethmoid and frontal bones.

The bones of the facial skeleton (14) are the vomer, two inferior nasal conchae, two nasal bones, two maxilla, the mandible, two palatine bones, two zygomatic bones, and two lacrimal bones. Some sources count a paired bone as one, or the maxilla as having two bones (as its parts); some sources include the hyoid bone or the three ossicles of the middle ear but the overall general consensus of the number of bones in the human skull is the stated twenty-two.

Some of these bones—the occipital, parietal, frontal, in the neurocranium, and the nasal, lacrimal, and vomer, in the facial skeleton are flat bones.

Cavities and foramina[edit]

CT scan of a human skull in 3D
The skull also contains sinuses, air-filled cavities known as paranasal sinuses, and numerous foramina. The sinuses are lined with respiratory epithelium. Their known functions are the lessening of the weight of the skull, the aiding of resonance to the voice and the warming and moistening of the air drawn into the nasal cavity.

The foramina are openings in the skull. The largest of these is the foramen magnum that allows the passage of the spinal cord as well as nerves and blood vessels.

Processes[edit]
The many processes of the skull include the mastoid process and the zygomatic processes.

Other vertebrates[edit]
Fenestrae[edit]

A Centrosaurus skull

Scheme of Spinosaurus skull

The fenestrae in the skull of the dinosaur Massospondylus
The fenestrae (from Latin, meaning windows) are openings in the skull.

Antorbital fenestra
Mandibular fenestra
Quadratojugal fenestra
Subsquamosal fenestra, an opening between two parts of the squamosal bone in some rodents
Temporal fenestra
The temporal fenestrae are anatomical features of the skulls of several types of amniotes, characterised by bilaterally symmetrical holes (fenestrae) in the temporal bone. Depending on the lineage of a given animal, two, one, or no pairs of temporal fenestrae may be present, above or below the postorbital and squamosal bones. The upper temporal fenestrae are also known as the supratemporal fenestrae, and the lower temporal fenestrae are also known as the infratemporal fenestrae. The presence and morphology of the temporal fenestra are critical for taxonomic classification of the synapsids, of which mammals are part.

Physiological speculation associates it with a rise in metabolic rates and an increase in jaw musculature. The earlier amniotes of the Carboniferous did not have temporal fenestrae but two more advanced lines did: the synapsids (mammal-like reptiles) and the diapsids (most reptiles and later birds). As time progressed, diapsids' and synapsids' temporal fenestrae became more modified and larger to make stronger bites and more jaw muscles. Dinosaurs, which are diapsids, have large advanced openings, and their descendants, the birds, have temporal fenestrae which have been modified. Mammals, which are synapsids, possess one fenestral opening in the skull, situated to the rear of the orbit.

Classification[edit]

Chimpanzee skull

Goat skull.
There are four types of amniote skull, classified by the number and location of their temporal fenestrae. These are:

Anapsida – no openings
Synapsida – one low opening (beneath the postorbital and squamosal bones)
Euryapsida – one high opening (above the postorbital and squamosal bones); euryapsids actually evolved from a diapsid configuration, losing their lower temporal fenestra.
Diapsida – two openings
Evolutionarily, they are related as follows:

Amniota
Class Synapsida
Order Therapsida
Class Mammalia – mammals
(Unranked) Sauropsida – reptiles and birds
Class Reptilia
Subclass Parareptilia
Infraclass Anapsida
Subclass Eureptilia
Infraclass Diapsida
Class Aves
Infraclass Euryapsida
Bones[edit]
The jugal is a skull bone found in most reptiles, amphibians, and birds. In mammals, the jugal is often called the zygomatic bone or malar bone.

The prefrontal bone is a bone separating the lacrimal and frontal bones in many tetrapod skulls.

Fish[edit]

Fish head parts, 1889, Fauna of British India, Sir Francis Day

Skull of a swordfish
The skull of fishes is formed from a series of only loosely connected bones. Lampreys and sharks only possess a cartilaginous endocranium, with both the upper and lower jaws being separate elements. Bony fishes have additional dermal bone, forming a more or less coherent skull roof in lungfish and holost fish. The lower jaw defines a chin.

The simpler structure is found in jawless fish, in which the cranium is normally represented by a trough-like basket of cartilaginous elements only partially enclosing the brain, and associated with the capsules for the inner ears and the single nostril. Distinctively, these fish have no jaws.[5]

Cartilaginous fish, such as sharks and rays, have also simple, and presumably primitive, skull structures. The cranium is a single structure forming a case around the brain, enclosing the lower surface and the sides, but always at least partially open at the top as a large fontanelle. The most anterior part of the cranium includes a forward plate of cartilage, the rostrum, and capsules to enclose the olfactory organs. Behind these are the orbits, and then an additional pair of capsules enclosing the structure of the inner ear. Finally, the skull tapers towards the rear, where the foramen magnum lies immediately above a single condyle, articulating with the first vertebra. There are, in addition, at various points throughout the cranium, smaller foramina for the cranial nerves. The jaws consist of separate hoops of cartilage, almost always distinct from the cranium proper.[5]

In ray-finned fish, there has also been considerable modification from the primitive pattern. The roof of the skull is generally well formed, and although the exact relationship of its bones to those of tetrapods is unclear, they are usually given similar names for convenience. Other elements of the skull, however, may be reduced; there is little cheek region behind the enlarged orbits, and little, if any bone in between them. The upper jaw is often formed largely from the premaxilla, with the maxilla itself located further back, and an additional bone, the symplectic, linking the jaw to the rest of the cranium.[6]

Although the skulls of fossil lobe-finned fish resemble those of the early tetrapods, the same cannot be said of those of the living lungfishes. The skull roof is not fully formed, and consists of multiple, somewhat irregularly shaped bones with no direct relationship to those of tetrapods. The upper jaw is formed from the pterygoids and vomers alone, all of which bear teeth. Much of the skull is formed from cartilage, and its overall structure is reduced.[6]

Tetrapods[edit]

Skull of Tiktaalik, an extinct genus transitional between lobe-finned fish and early tetrapods
The skulls of the earliest tetrapods closely resembled those of their ancestors amongst the lobe-finned fishes. The skull roof is formed of a series of plate-like bones, including the maxilla, frontals, parietals, and lacrimals, among others. It is overlaying the endocranium, corresponding to the cartilaginous skull in sharks and rays. The various separate bones that compose the temporal bone of humans are also part of the skull roof series. A further plate composed of four pairs of bones forms the roof of the mouth; these include the vomer and palatine bones. The base of the cranium is formed from a ring of bones surrounding the foramen magnum and a median bone lying further forward; these are homologous with the occipital bone and parts of the sphenoid in mammals. Finally, the lower jaw is composed of multiple bones, only the most anterior of which (the dentary) is homologous with the mammalian mandible.[6]

In living tetrapods, a great many of the original bones have either disappeared or fused into one another in various arrangements.

Birds[edit]

Cuckoo skull
Birds have a diapsid skull, as in reptiles, with a prelachrymal fossa (present in some reptiles). The skull has a single occipital condyle.[7] The skull consists of five major bones: the frontal (top of head), parietal (back of head), premaxillary and nasal (top beak), and the mandible (bottom beak). The skull of a normal bird usually weighs about 1% of the bird's total bodyweight. The eye occupies a considerable amount of the skull and is surrounded by a sclerotic eye-ring, a ring of tiny bones. This characteristic is also seen in reptiles.

Amphibians[edit]

Amphibians skulls, Hans Gadow, 1909 Amphibia and Reptiles
Living amphibians typically have greatly reduced skulls, with many of the bones either absent or wholly or partly replaced by cartilage.[6] In mammals and birds, in particular, modifications of the skull occurred to allow for the expansion of the brain. The fusion between the various bones is especially notable in birds, in which the individual structures may be difficult to identify.

Development[edit]

Skull of a new-born child from the side
The skull is a complex structure; its bones are formed both by intramembranous and endochondral ossification. The skull roof bones, comprising the bones of the facial skeleton and the sides and roof of the neurocranium, are dermal bones formed by intramembranous ossification, though the temporal bones are formed by endochondral ossification. The endocranium, the bones supporting the brain (the occipital, sphenoid, and ethmoid) are largely formed by endochondral ossification. Thus frontal and parietal bones are purely membranous.[8] The geometry of the skull base and its fossae, the anterior, middle and posterior cranial fossae changes rapidly. The anterior cranial fossa changes especially during the first trimester of pregnancy and skull defects can often develop during this time.[9]

At birth, the human skull is made up of 44 separate bony elements. During development, many of these bony elements gradually fuse together into solid bone (for example, the frontal bone). The bones of the roof of the skull are initially separated by regions of dense connective tissue called fontanelles. There are six fontanelles: one anterior (or frontal), one posterior (or occipital), two sphenoid (or anterolateral), and two mastoid (or posterolateral). At birth, these regions are fibrous and moveable, necessary for birth and later growth. This growth can put a large amount of tension on the "obstetrical hinge", which is where the squamous and lateral parts of the occipital bone meet. A possible complication of this tension is rupture of the great cerebral vein. As growth and ossification progress, the connective tissue of the fontanelles is invaded and replaced by bone creating sutures. The five sutures are the two squamous sutures, one coronal, one lambdoid, and one sagittal suture. The posterior fontanelle usually closes by eight weeks, but the anterior fontanel can remain open up to eighteen months. The anterior fontanelle is located at the junction of the frontal and parietal bones; it is a "soft spot" on a baby's forehead. Careful observation will show that you can count a baby's heart rate by observing the pulse pulsing softly through the anterior fontanelle.

The skull in the neonate is large in proportion to other parts of the body. The facial skeleton is one seventh of the size of the calvaria. (In the adult it is half the size). The base of the skull is short and narrow, though the inner ear is almost adult size.[10]

Clinical significance[edit]
Craniosynostosis is a condition in which one or more of the fibrous sutures in an infant skull prematurely fuses,[11] and changes the growth pattern of the skull.[12] Because the skull cannot expand perpendicular to the fused suture, it grows more in the parallel direction.[12] Sometimes the resulting growth pattern provides the necessary space for the growing brain, but results in an abnormal head shape and abnormal facial features.[12] In cases in which the compensation does not effectively provide enough space for the growing brain, craniosynostosis results in increased intracranial pressure leading possibly to visual impairment, sleeping impairment, eating difficulties, or an impairment of mental development.[13]

A copper beaten skull is a phenomenon wherein intense intracranial pressure disfigures the internal surface of the skull.[14] The name comes from the fact that the inner skull has the appearance of having been beaten with a ball-peen hammer, such as is often used by coppersmiths. The condition is most common in children.

Injuries and treatment[edit]
Injuries to the brain can be life-threatening. Normally the skull protects the brain from damage through its hard unyieldingness; the skull is one of the least deformable structures found in nature with it needing the force of about 1 ton to reduce the diameter of the skull by 1 cm.[15] In some cases, however, of head injury, there can be raised intracranial pressure through mechanisms such as a subdural haematoma. In these cases the raised intracranial pressure can cause herniation of the brain out of the foramen magnum ("coning") because there is no space for the brain to expand; this can result in significant brain damage or death unless an urgent operation is performed to relieve the pressure. This is why patients with concussion must be watched extremely carefully.

Dating back to Neolithic times, a skull operation called trepanning was sometimes performed. This involved drilling a burr hole in the cranium. Examination of skulls from this period reveals that the patients sometimes survived for many years afterward. It seems likely that trepanning was also performed purely for ritualistic or religious reasons. Nowadays this procedure is still used but is normally called a craniectomy.

In March 2013, for the first time in the U.S., researchers replaced a large percentage of a patient's skull with a precision, 3D-printed polymer implant.[16] About 9 months later, the first complete cranium replacement with a 3D-printed plastic insert was performed on a Dutch woman. She had been suffering from hyperostosis, which increased the thickness of her skull and compressed her brain.[17]

A study conducted in 2018 by the researchers of Harvard Medical School in Boston, funded by National Institutes of Health (NIH) suggested that instead of travelling via blood, there are "tiny channels" in the skull through which the immune cells combined with the bone marrow reach the areas of inflammation after an injury to the brain tissues.[18]

Transgender procedures[edit]
Surgical alteration of sexually dimorphic skull features may be carried out as a part of facial feminization surgery, a set of reconstructive surgical procedures that can alter male facial features to bring them closer in shape and size to typical female facial features.[19][20] These procedures can be an important part of the treatment of transgender people for gender dysphoria.[21][22]

Society and culture[edit]

A skull is the symbol of penance, Silk embroidery (17th century)
Artificial cranial deformation is a largely historical practice of some cultures. Cords and wooden boards would be used to apply pressure to an infant's skull and alter its shape, sometimes quite significantly. This procedure would begin just after birth and would be carried on for several years.[citation needed]

Osteology[edit]
Like the face, the skull and teeth can also indicate a person's life history and origin. Forensic scientists and archaeologists use metric and nonmetric traits to estimate what the bearer of the skull looked like. When a significant amount of bones are found, such as at Spitalfields in the UK and Jōmon shell mounds in Japan, osteologists can use traits, such as the proportions of length, height and width, to know the relationships of the population of the study with other living or extinct populations.[citation needed]

The German physician Franz Joseph Gall in around 1800 formulated the theory of phrenology, which attempted to show that specific features of the skull are associated with certain personality traits or intellectual capabilities of its owner. His theory is now considered to be pseudoscientific.[citation needed]

Sexual dimorphism[edit]
Main article: Sexual dimorphism
In the mid-nineteenth century, anthropologists found it crucial to distinguish between male and female skulls. An anthropologist of the time, James McGrigor Allan, argued that the female brain was similar to that of an animal.[23] This allowed anthropologists to declare that women were in fact more emotional and less rational than men. McGrigor then concluded that women's brains were more analogous to infants, thus deeming them inferior at the time.[23] To further these claims of female inferiority and silence the feminists of the time, other anthropologists joined in on the studies of the female skull. These cranial measurements are the basis of what is known as craniology. These cranial measurements were also used to draw a connection between women and black people.[23]

Research has shown that while in early life there is little difference between male and female skulls, in adulthood male skulls tend to be larger and more robust than female skulls, which are lighter and smaller, with a cranial capacity about 10 percent less than that of the male.[24] However, later studies show that women's skulls are slightly thicker and thus men may be more susceptible to head injury than women.[25][26] However, other studies show this may not be true and may even be the opposite, with men having slightly thicker skulls overall.[27][28][29] Men's skulls have also been shown to be more dense, which may aid in preventing head injury.[30]

Male skulls can have more prominent supraorbital ridges, a more prominent glabella, and more prominent temporal lines. Female skulls generally have rounder orbits, and narrower jaws. Male skulls on average have larger, broader palates, squarer orbits, larger mastoid processes, larger sinuses, and larger occipital condyles than those of females. Male mandibles typically have squarer chins and thicker, rougher muscle attachments than female mandibles.[citation needed]

Craniometry[edit]
The cephalic index is the ratio of the width of the head, multiplied by 100 and divided by its length (front to back). The index is also used to categorize animals, especially dogs and cats. The width is usually measured just below the parietal eminence, and the length from the glabella to the occipital point.

Humans may be:

Dolichocephalic — long-headed
Mesaticephalic — medium-headed
Brachycephalic — short-headed[10]

Terminology[edit]
Chondrocranium, a primitive cartilagionous skeletal structure
Endocranium
Epicranium
Pericranium, a membrane that lines the outer surface of the cranium
History[edit]
Trepanning, a practice in which a hole is created in the skull, has been described as the oldest surgical procedure for which there is archaeological evidence,[31] found in the forms of cave paintings and human remains. At one burial site in France dated to 6500 BCE, 40 out of 120 prehistoric skulls found had trepanation holes." (wikipedia.org)

"The skeleton is the body part that provides support, shape and protection to the soft tissues and delicate organs of animals. There are several different skeletal types: the exoskeleton, which is the stable outer shell of an organism, the endoskeleton, which forms the support structure inside the body, the hydroskeleton, a flexible skeleton supported by fluid pressure, and the cytoskeleton present in the cytoplasm of all cells, including bacteria, and archaea. The term comes from Greek σκελετός (skeletós), meaning 'dried up'....

Types of skeletons[edit]
There are two major types of skeletons: solid and fluid. Solid skeletons can be internal, called an endoskeleton, or external, called an exoskeleton, and may be further classified as pliant (elastic/movable) or rigid (hard/non-movable).[2] Fluid skeletons are always internal.

Exoskeleton[edit]
Main article: Exoskeleton

Exoskeleton of an ant
Exoskeletons are external, and are found in many invertebrates; they enclose and protect the soft tissues and organs of the body. Some kinds of exoskeletons undergo periodic moulting or ecdysis as the animal grows, as is the case in many arthropods including insects and crustaceans.

The exoskeleton of insects is not only a form of protection, but also serves as a surface for muscle attachment, as a watertight protection against drying, and as a sense organ to interact with the environment. The shell of mollusks also performs all of the same functions, except that in most cases it does not contain sense organs.

An external skeleton can be quite heavy in relation to the overall mass of an animal, so on land, organisms that have an exoskeleton are mostly relatively small. Somewhat larger aquatic animals can support an exoskeleton because weight is less of a consideration underwater. The southern giant clam, a species of extremely large saltwater clam in the Pacific Ocean, has a shell that is massive in both size and weight. Syrinx aruanus is a species of sea snail with a very large shell.

Endoskeleton[edit]
Main article: Endoskeleton

Endoskeleton of a bat.
The endoskeleton is the internal support structure of an animal, composed of mineralized tissue and is typical of vertebrates. Endoskeletons vary in complexity from functioning purely for support (as in the case of sponges), to serving as an attachment site for muscles and a mechanism for transmitting muscular forces. A true endoskeleton is derived from mesodermal tissue. Such a skeleton is present in echinoderms and chordates.

Pliant skeletons[edit]
Pliant skeletons are capable of movement; thus, when stress is applied to the skeletal structure, it deforms and then reverts to its original shape. This skeletal structure is used in some invertebrates, for instance in the hinge of bivalve shells or the mesoglea of cnidarians such as jellyfish. Pliant skeletons are beneficial because only muscle contractions are needed to bend the skeleton; upon muscle relaxation, the skeleton will return to its original shape. Cartilage is one material that a pliant skeleton may be composed of, but most pliant skeletons are formed from a mixture of proteins, polysaccharides, and water.[2] For additional structure or protection, pliant skeletons may be supported by rigid skeletons. Organisms that have pliant skeletons typically live in water, which supports body structure in the absence of a rigid skeleton.[3]

Rigid skeletons[edit]
Rigid skeletons are not capable of movement when stressed, creating a strong support system most common in terrestrial animals. Such a skeleton type used by animals that live in water are more for protection (such as barnacle and snail shells) or for fast-moving animals that require additional support of musculature needed for swimming through water. Rigid skeletons are formed from materials including chitin (in arthropods), calcium compounds such as calcium carbonate (in stony corals and mollusks) and silicate (for diatoms and radiolarians).

Cytoskeleton[edit]
Main article: Cytoskeleton
The cytoskeleton (gr. kytos = cell) is used to stabilize and preserve the form of the cells. It is a dynamic structure that maintains cell shape, protects the cell, enables cellular motion (using structures such as flagella, cilia and lamellipodia), and plays important roles in both intracellular transport (the movement of vesicles and organelles, for example) and cellular division.

Fluid skeletons[edit]
Hydrostatic skeleton (hydroskeleton)[edit]
Main article: Hydrostatic skeleton
A hydrostatic skeleton is a semi-rigid, soft tissue structure filled with liquid under pressure, surrounded by muscles. Longitudinal and circular muscles around their body sectors allow movement by alternate lengthening and contractions along their lengths. A common example of this is the earthworm.

Organisms with skeletons[edit]
Invertebrates[edit]
The endoskeletons of echinoderms and some other soft-bodied invertebrates such as jellyfish and earthworms are also termed hydrostatic; a body cavity the coelom is filled with coelomic fluid and the pressure from this fluid acts together with the surrounding muscles to change the organism's shape and produce movement.

Sponges[edit]
The skeleton of sponges consists of microscopic calcareous or silicious spicules. The demosponges include 90% of all species of sponges. Their "skeletons" are made of spicules consisting of fibers of the protein spongin, the mineral silica, or both. Where spicules of silica are present, they have a different shape from those in the otherwise similar glass sponges.[4]

Echinoderms[edit]
The skeleton of the echinoderms, which include, among other things, the starfish, is composed of calcite and a small amount of magnesium oxide. It lies below the epidermis in the mesoderm and is within cell clusters of frame-forming cells. This structure formed is porous and therefore firm and at the same time light. It coalesces into small calcareous ossicles (bony plates), which can grow in all directions and thus can replace the loss of a body part. Connected by joints, the individual skeletal parts can be moved by the muscles.

Vertebrates[edit]

Pithecometra: From Thomas Huxley's 1863 Evidence as to Man's Place in Nature, the compared skeletons of apes to humans.
In most vertebrates, the main skeletal component is referred to as bone. These bones compose a unique skeletal system for each type of animal. Another important component is cartilage which in mammals is found mainly in the joint areas. In other animals, such as the cartilaginous fishes, which include the sharks, the skeleton is composed entirely of cartilage. The segmental pattern of the skeleton is present in all vertebrates (mammals, birds, fish, reptiles and amphibians) with basic units being repeated. This segmental pattern is particularly evident in the vertebral column and the ribcage.

Bones in addition to supporting the body also serve, at the cellular level, as calcium and phosphate storage.

Fish[edit]
Main article: Fish anatomy
The skeleton, which forms the support structure inside the fish is either made of cartilage as in the (Chondrichthyes), or bones as in the (Osteichthyes). The main skeletal element is the vertebral column, composed of articulating vertebrae which are lightweight yet strong. The ribs attach to the spine and there are no limbs or limb girdles. They are supported only by the muscles. The main external features of the fish, the fins, are composed of either bony or soft spines called rays, which with the exception of the caudal fin (tail fin), have no direct connection with the spine. They are supported by the muscles which compose the main part of the trunk.

Birds[edit]
Main article: Bird anatomy
The bird skeleton is highly adapted for flight. It is extremely lightweight, yet still strong enough to withstand the stresses of taking off, flying, and landing. One key adaptation is the fusing of bones into single ossifications, such as the pygostyle. Because of this, birds usually have a smaller number of bones than other terrestrial vertebrates. Birds also lack teeth or even a true jaw, instead having evolved a beak, which is far more lightweight. The beaks of many baby birds have a projection called an egg tooth, which facilitates their exit from the amniotic egg.

Marine mammals[edit]

Californian sea lion
To facilitate the movement of marine mammals in water, the hind legs were either lost altogether, as in the whales and manatees, or united in a single tail fin as in the pinnipeds (seals). In the whale, the cervical vertebrae are typically fused, an adaptation trading flexibility for stability during swimming.[5][6]

Humans[edit]
Main article: Human skeleton

Study of Skeletons, c. 1510, by Leonardo da Vinci
The skeleton consists of both fused and individual bones supported and supplemented by ligaments, tendons, muscles and cartilage. It serves as a scaffold which supports organs, anchors muscles, and protects organs such as the brain, lungs, heart and spinal cord. Although the teeth do not consist of tissue commonly found in bones, the teeth are usually considered as members of the skeletal system.[7] The biggest bone in the body is the femur in the upper leg, and the smallest is the stapes bone in the middle ear. In an adult, the skeleton comprises around 14% of the total body weight,[8] and half of this weight is water.

Fused bones include those of the pelvis and the cranium. Not all bones are interconnected directly: There are three bones in each middle ear called the ossicles that articulate only with each other. The hyoid bone, which is located in the neck and serves as the point of attachment for the tongue, does not articulate with any other bones in the body, being supported by muscles and ligaments.

There are 206 bones in the adult human skeleton, although this number depends on whether the pelvic bones (the hip bones on each side) are counted as one or three bones on each side (ilium, ischium, and pubis), whether the coccyx or tail bone is counted as one or four separate bones, and does not count the variable wormian bones between skull sutures. Similarly, the sacrum is usually counted as a single bone, rather than five fused vertebrae. There is also a variable number of small sesamoid bones, commonly found in tendons. The patella or kneecap on each side is an example of a larger sesamoid bone. The patellae are counted in the total, as they are constant. The number of bones varies between individuals and with age – newborn babies have over 270 bones[9][10][11] some of which fuse together. These bones are organized into a longitudinal axis, the axial skeleton, to which the appendicular skeleton is attached.[12]

The human skeleton takes 20 years before it is fully developed, and the bones contain marrow, which produces blood cells.

There exist several general differences between the male and female skeletons. The male skeleton, for example, is generally larger and heavier than the female skeleton. In the female skeleton, the bones of the skull are generally less angular. The female skeleton also has wider and shorter breastbone and slimmer wrists. There exist significant differences between the male and female pelvis which are related to the female's pregnancy and childbirth capabilities. The female pelvis is wider and shallower than the male pelvis. Female pelvises also have an enlarged pelvic outlet and a wider and more circular pelvic inlet. The angle between the pubic bones is known to be sharper in males, which results in a more circular, narrower, and near heart-shaped pelvis.[13][14]

Bones and cartilage[edit]
Bone[edit]
Main article: Bone
Bones are rigid organs that form part of the endoskeleton of vertebrates. They function to move, support, and protect the various organs of the body, produce red and white blood cells and store minerals. Bone tissue is a type of dense connective tissue. Bones have a variety of shapes with a complex internal and external structure they are also lightweight, yet strong and hard. One of the types of tissue that makes up bone tissue is mineralized tissue and this gives it rigidity and a honeycomb-like three-dimensional internal structure. Other types of tissue found in bones include marrow, endosteum and periosteum, nerves, blood vessels and cartilage.

Cartilage[edit]
Main article: Cartilage
During embryonic development the precursor to bone development is cartilage that mostly becomes replaced by bone, after flesh such as muscle has formed around it. Cartilage is a stiff and inflexible connective tissue found in many areas including the joints between bones, the rib cage, the ear, the nose, the elbow, the knee, the ankle, the bronchial tubes and the intervertebral discs. It is not as hard and rigid as bone but is stiffer and less flexible than muscle.

Cartilage is composed of specialized cells called chondrocytes that produce a large amount of extracellular matrix composed of Type II collagen (except fibrocartilage which also contains type I collagen) fibers, abundant ground substance rich in proteoglycans, and elastin fibers. Cartilage is classified in three types, elastic cartilage, hyaline cartilage and fibrocartilage, which differ in the relative amounts of these three main components.

Unlike other connective tissues, cartilage does not contain blood vessels. The chondrocytes are supplied by diffusion, helped by the pumping action generated by compression of the articular cartilage or flexion of the elastic cartilage. Thus, compared to other connective tissues, cartilage grows and repairs more slowly.

Culture[edit]
In Western culture, the human skeleton is oftentimes seen as a fearful symbol of death and the paranormal. It is a popular motif in the holiday Halloween, as well as Day of the Dead.

Movies[edit]
Skeletons can also be found in movies. Skeletons in movies can be often depicted coming to life, commonly in horror movies. Skeletons can also be depicted in movies wearing chainmail, helmets, and shields. Commonly holding an axe or sword. In these types of movies they are commonly getting attacked, "killed", or fighting with character(s). Skeletons can also be found in a more "welcoming" and "friendly" way in movies. Such as, playing as a decoration, a Halloween costume/face paint, ETC. Another way skeletons can be shown in movies is debatably more common than the other depictions is a sign of severe burning from things such as chemicals, fire, and acid. This can also be a case of deterioration over time." (wikipedia.org)

"Iridescence (also known as goniochromism) is the phenomenon of certain surfaces that appear to gradually change color as the angle of view or the angle of illumination changes. Examples of iridescence include soap bubbles, feathers, butterfly wings and seashell nacre, as well as certain minerals. It is often created by structural coloration (microstructures that interfere with light).

Pearlescence is a related effect where some or all of the reflected light is white, where iridescent effects produce only other colours. The term pearlescent is used to describe certain paint finishes, usually in the automotive industry, which actually produce iridescent effects....

Etymology[edit]
The word iridescence is derived in part from the Greek word ἶρις îris (gen. ἴριδος íridos), meaning rainbow, and is combined with the Latin suffix -escent, meaning "having a tendency toward".[1] Iris in turn derives from the goddess Iris of Greek mythology, who is the personification of the rainbow and acted as a messenger of the gods. Goniochromism is derived from the Greek words gonia, meaning "angle", and chroma, meaning "colour".

Mechanisms[edit]

Fuel on top of water creates a thin film, which interferes with the light, producing different colours. The different bands represent different thicknesses in the film.

An iridescent biofilm on the surface of a fishtank diffracts the reflected light, displaying the entire spectrum of colours. Red is seen from longer angles of incidence than blue.
Further information: Structural coloration, thin-film interference, and diffraction
Iridescence is an optical phenomenon of surfaces in which hue changes with the angle of observation and the angle of illumination.[2][3] It is often caused by multiple reflections from two or more semi-transparent surfaces in which phase shift and interference of the reflections modulates the incidental light (by amplifying or attenuating some frequencies more than others).[2][4] The thickness of the layers of the material determines the interference pattern. Iridescence can for example be due to thin-film interference, the functional analogue of selective wavelength attenuation as seen with the Fabry–Pérot interferometer, and can be seen in oil films on water and soap bubbles. Iridescence is also found in plants, animals and many other items. The range of colours of natural iridescent objects can be narrow, for example shifting between two or three colours as the viewing angle changes,[5][6]

Iridescence can also be created by diffraction. This is found in items like CDs, DVDs, some types of prisms, or cloud iridescence.[7] In the case of diffraction, the entire rainbow of colours will typically be observed as the viewing angle changes. In biology, this type of iridescence results from the formation of diffraction gratings on the surface, such as the long rows of cells in striated muscle, or the specialized abdominal scales of peacock spider Maratus robinsoni and M. chrysomelas.[8] Some types of flower petals can also generate a diffraction grating, but the iridescence is not visible to humans and flower-visiting insects as the diffraction signal is masked by the coloration due to plant pigments.[9][10][11]

In biological (and biomimetic) uses, colours produced other than with pigments or dyes are called structural coloration. Microstructures, often multilayered, are used to produce bright but sometimes non-iridescent colours: quite elaborate arrangements are needed to avoid reflecting different colours in different directions.[12] Structural coloration has been understood in general terms since Robert Hooke's 1665 book Micrographia, where Hooke correctly noted that since the iridescence of a peacock's feather was lost when it was plunged into water, but reappeared when it was returned to the air, pigments could not be responsible.[13][14] It was later found that iridescence in the peacock is due to a complex photonic crystal.[15]

Pearlescence[edit]
Pearlescence is an effect related to iridescence and has a similar cause. Structures within a surface cause light to be reflected back, but in the case of pearlescence some or all of the light is white.[16] Artificial pigments and paints showing an iridescent effect are often described as pearlescent, for example when used for car paints." (wikipedia.org)

"Color (American English), or colour (Commonwealth English), is the characteristic of visual perception described through color categories, with names such as red, orange, yellow, green, blue, or purple. This perception of color derives from the stimulation of photoreceptor cells (in particular cone cells in the human eye and other vertebrate eyes) by electromagnetic radiation (in the visible spectrum in the case of humans). Color categories and physical specifications of color are associated with objects through the wavelengths of the light that is reflected from them and their intensities. This reflection is governed by the object's physical properties such as light absorption, emission spectra, etc.

By defining a color space, colors can be identified numerically by coordinates, which in 1931 were also named in global agreement with internationally agreed color names like mentioned above (red, orange, etc.) by the International Commission on Illumination. The RGB color space for instance is a color space corresponding to human trichromacy and to the three cone cell types that respond to three bands of light: long wavelengths, peaking near 564–580 nm (red); medium-wavelength, peaking near 534–545 nm (green); and short-wavelength light, near 420–440 nm (blue).[1][2] There may also be more than three color dimensions in other color spaces, such as in the CMYK color model, wherein one of the dimensions relates to a color's colorfulness).

The photo-receptivity of the "eyes" of other species also varies considerably from that of humans and so results in correspondingly different color perceptions that cannot readily be compared to one another. Honey bees and bumblebees have trichromatic color vision sensitive to ultraviolet but insensitive to red. Papilio butterflies possess six types of photoreceptors and may have pentachromatic vision.[3] The most complex color vision system in the animal kingdom has been found in stomatopods (such as the mantis shrimp) with up to 12 spectral receptor types thought to work as multiple dichromatic units.[4]

The science of color is sometimes called chromatics, colorimetry, or simply color science. It includes the study of the perception of color by the human eye and brain, the origin of color in materials, color theory in art, and the physics of electromagnetic radiation in the visible range (that is, what is commonly referred to simply as light)....
Physics of color

Continuous optical spectrum rendered into the sRGB color space.
The colors of the visible light spectrum[5]
Color Wavelength
interval Frequency
interval
Red ~ 700–635 nm ~ 430–480 THz
Orange ~ 635–590 nm ~ 480–510 THz
Yellow ~ 590–560 nm ~ 510–540 THz
Green ~ 560–520 nm ~ 540–580 THz
Cyan ~ 520–490 nm ~ 580–610 THz
Blue ~ 490–450 nm ~ 610–670 THz
Violet ~ 450–400 nm ~ 670–750 THz
Color, wavelength, frequency and energy of light
Color
λ
\lambda \,\!
(nm)
ν
\nu \,\!
(THz)
ν
b
\nu_b \,\!
(μm−1)
E
E \,\!
(eV)
E
E \,\!
(kJ mol−1)
Infrared >1000 <300 <1.00 <1.24 <120
Red 700 428 1.43 1.77 171
Orange 620 484 1.61 2.00 193
Yellow 580 517 1.72 2.14 206
Green 530 566 1.89 2.34 226
Cyan 500 600
Blue 470 638 2.13 2.64 254
Violet (visible) 420 714 2.38 2.95 285
Near ultraviolet 300 1000 3.33 4.15 400
Far ultraviolet <200 >1500 >5.00 >6.20 >598
Electromagnetic radiation is characterized by its wavelength (or frequency) and its intensity. When the wavelength is within the visible spectrum (the range of wavelengths humans can perceive, approximately from 390 nm to 700 nm), it is known as "visible light".

Most light sources emit light at many different wavelengths; a source's spectrum is a distribution giving its intensity at each wavelength. Although the spectrum of light arriving at the eye from a given direction determines the color sensation in that direction, there are many more possible spectral combinations than color sensations. In fact, one may formally define a color as a class of spectra that give rise to the same color sensation, although such classes would vary widely among different species, and to a lesser extent among individuals within the same species. In each such class the members are called metamers of the color in question. This effect can be visualized by comparing the light sources' spectral power distributions and the resulting colors.

Spectral colors
The familiar colors of the rainbow in the spectrum—named using the Latin word for appearance or apparition by Isaac Newton in 1671—include all those colors that can be produced by visible light of a single wavelength only, the pure spectral or monochromatic colors. The table at right shows approximate frequencies (in terahertz) and wavelengths (in nanometers) for various pure spectral colors. The wavelengths listed are as measured in air or vacuum (see refractive index).

The color table should not be interpreted as a definitive list—the pure spectral colors form a continuous spectrum, and how it is divided into distinct colors linguistically is a matter of culture and historical contingency (although people everywhere have been shown to perceive colors in the same way[6]). A common list identifies six main bands: red, orange, yellow, green, blue, and violet. Newton's conception included a seventh color, indigo, between blue and violet. It is possible that what Newton referred to as blue is nearer to what today is known as cyan, and that indigo was simply the dark blue of the indigo dye that was being imported at the time.[7]

The intensity of a spectral color, relative to the context in which it is viewed, may alter its perception considerably; for example, a low-intensity orange-yellow is brown, and a low-intensity yellow-green is olive green.

Color of objects
The color of an object depends on both the physics of the object in its environment and the characteristics of the perceiving eye and brain. Physically, objects can be said to have the color of the light leaving their surfaces, which normally depends on the spectrum of the incident illumination and the reflectance properties of the surface, as well as potentially on the angles of illumination and viewing. Some objects not only reflect light, but also transmit light or emit light themselves, which also contributes to the color. A viewer's perception of the object's color depends not only on the spectrum of the light leaving its surface, but also on a host of contextual cues, so that color differences between objects can be discerned mostly independent of the lighting spectrum, viewing angle, etc. This effect is known as color constancy.


The upper disk and the lower disk have exactly the same objective color, and are in identical gray surroundings; based on context differences, humans perceive the squares as having different reflectances, and may interpret the colors as different color categories; see checker shadow illusion.
Some generalizations of the physics can be drawn, neglecting perceptual effects for now:

Light arriving at an opaque surface is either reflected "specularly" (that is, in the manner of a mirror), scattered (that is, reflected with diffuse scattering), or absorbed—or some combination of these.
Opaque objects that do not reflect specularly (which tend to have rough surfaces) have their color determined by which wavelengths of light they scatter strongly (with the light that is not scattered being absorbed). If objects scatter all wavelengths with roughly equal strength, they appear white. If they absorb all wavelengths, they appear black.[8]
Opaque objects that specularly reflect light of different wavelengths with different efficiencies look like mirrors tinted with colors determined by those differences. An object that reflects some fraction of impinging light and absorbs the rest may look black but also be faintly reflective; examples are black objects coated with layers of enamel or lacquer.
Objects that transmit light are either translucent (scattering the transmitted light) or transparent (not scattering the transmitted light). If they also absorb (or reflect) light of various wavelengths differentially, they appear tinted with a color determined by the nature of that absorption (or that reflectance).
Objects may emit light that they generate from having excited electrons, rather than merely reflecting or transmitting light. The electrons may be excited due to elevated temperature (incandescence), as a result of chemical reactions (chemoluminescence), after absorbing light of other frequencies ("fluorescence" or "phosphorescence") or from electrical contacts as in light-emitting diodes, or other light sources.
To summarize, the color of an object is a complex result of its surface properties, its transmission properties, and its emission properties, all of which contribute to the mix of wavelengths in the light leaving the surface of the object. The perceived color is then further conditioned by the nature of the ambient illumination, and by the color properties of other objects nearby, and via other characteristics of the perceiving eye and brain.

Perception

When viewed in full size, this image contains about 16 million pixels, each corresponding to a different color on the full set of RGB colors. The human eye can distinguish about 10 million different colors.[9]
Development of theories of color vision
Main article: Color theory
Although Aristotle and other ancient scientists had already written on the nature of light and color vision, it was not until Newton that light was identified as the source of the color sensation. In 1810, Goethe published his comprehensive Theory of Colors in which he ascribed physiological effects to color that are now understood as psychological.

In 1801 Thomas Young proposed his trichromatic theory, based on the observation that any color could be matched with a combination of three lights. This theory was later refined by James Clerk Maxwell and Hermann von Helmholtz. As Helmholtz puts it, "the principles of Newton's law of mixture were experimentally confirmed by Maxwell in 1856. Young's theory of color sensations, like so much else that this marvelous investigator achieved in advance of his time, remained unnoticed until Maxwell directed attention to it."[10]

At the same time as Helmholtz, Ewald Hering developed the opponent process theory of color, noting that color blindness and afterimages typically come in opponent pairs (red-green, blue-orange, yellow-violet, and black-white). Ultimately these two theories were synthesized in 1957 by Hurvich and Jameson, who showed that retinal processing corresponds to the trichromatic theory, while processing at the level of the lateral geniculate nucleus corresponds to the opponent theory.[11]

In 1931, an international group of experts known as the Commission internationale de l'éclairage (CIE) developed a mathematical color model, which mapped out the space of observable colors and assigned a set of three numbers to each.

Color in the eye
Main article: Color vision

Normalized typical human cone cell responses (S, M, and L types) to monochromatic spectral stimuli
The ability of the human eye to distinguish colors is based upon the varying sensitivity of different cells in the retina to light of different wavelengths. Humans are trichromatic—the retina contains three types of color receptor cells, or cones. One type, relatively distinct from the other two, is most responsive to light that is perceived as blue or blue-violet, with wavelengths around 450 nm; cones of this type are sometimes called short-wavelength cones or S cones (or misleadingly, blue cones). The other two types are closely related genetically and chemically: middle-wavelength cones, M cones, or green cones are most sensitive to light perceived as green, with wavelengths around 540 nm, while the long-wavelength cones, L cones, or red cones, are most sensitive to light that is perceived as greenish yellow, with wavelengths around 570 nm.

Light, no matter how complex its composition of wavelengths, is reduced to three color components by the eye. Each cone type adheres to the principle of univariance, which is that each cone's output is determined by the amount of light that falls on it over all wavelengths. For each location in the visual field, the three types of cones yield three signals based on the extent to which each is stimulated. These amounts of stimulation are sometimes called tristimulus values.

The response curve as a function of wavelength varies for each type of cone. Because the curves overlap, some tristimulus values do not occur for any incoming light combination. For example, it is not possible to stimulate only the mid-wavelength (so-called "green") cones; the other cones will inevitably be stimulated to some degree at the same time. The set of all possible tristimulus values determines the human color space. It has been estimated that humans can distinguish roughly 10 million different colors.[9]

The other type of light-sensitive cell in the eye, the rod, has a different response curve. In normal situations, when light is bright enough to strongly stimulate the cones, rods play virtually no role in vision at all.[12] On the other hand, in dim light, the cones are understimulated leaving only the signal from the rods, resulting in a colorless response. (Furthermore, the rods are barely sensitive to light in the "red" range.) In certain conditions of intermediate illumination, the rod response and a weak cone response can together result in color discriminations not accounted for by cone responses alone. These effects, combined, are summarized also in the Kruithof curve, that describes the change of color perception and pleasingness of light as function of temperature and intensity.

Color in the brain
Main article: Color vision

The visual dorsal stream (green) and ventral stream (purple) are shown. The ventral stream is responsible for color perception.
While the mechanisms of color vision at the level of the retina are well-described in terms of tristimulus values, color processing after that point is organized differently. A dominant theory of color vision proposes that color information is transmitted out of the eye by three opponent processes, or opponent channels, each constructed from the raw output of the cones: a red–green channel, a blue–yellow channel, and a black–white "luminance" channel. This theory has been supported by neurobiology, and accounts for the structure of our subjective color experience. Specifically, it explains why humans cannot perceive a "reddish green" or "yellowish blue", and it predicts the color wheel: it is the collection of colors for which at least one of the two color channels measures a value at one of its extremes.

The exact nature of color perception beyond the processing already described, and indeed the status of color as a feature of the perceived world or rather as a feature of our perception of the world—a type of qualia—is a matter of complex and continuing philosophical dispute.

Nonstandard color perception
Color deficiency
Main article: Color blindness
If one or more types of a person's color-sensing cones are missing or less responsive than normal to incoming light, that person can distinguish fewer colors and is said to be color deficient or color blind (though this latter term can be misleading; almost all color deficient individuals can distinguish at least some colors). Some kinds of color deficiency are caused by anomalies in the number or nature of cones in the retina. Others (like central or cortical achromatopsia) are caused by neural anomalies in those parts of the brain where visual processing takes place.

Tetrachromacy
Main article: Tetrachromacy
While most humans are trichromatic (having three types of color receptors), many animals, known as tetrachromats, have four types. These include some species of spiders, most marsupials, birds, reptiles, and many species of fish. Other species are sensitive to only two axes of color or do not perceive color at all; these are called dichromats and monochromats respectively. A distinction is made between retinal tetrachromacy (having four pigments in cone cells in the retina, compared to three in trichromats) and functional tetrachromacy (having the ability to make enhanced color discriminations based on that retinal difference). As many as half of all women are retinal tetrachromats.[13]:p.256 The phenomenon arises when an individual receives two slightly different copies of the gene for either the medium- or long-wavelength cones, which are carried on the X chromosome. To have two different genes, a person must have two X chromosomes, which is why the phenomenon only occurs in women.[13] There is one scholarly report that confirms the existence of a functional tetrachromat.[14]

Synesthesia
In certain forms of synesthesia/ideasthesia, perceiving letters and numbers (grapheme–color synesthesia) or hearing musical sounds (music–color synesthesia) will lead to the unusual additional experiences of seeing colors. Behavioral and functional neuroimaging experiments have demonstrated that these color experiences lead to changes in behavioral tasks and lead to increased activation of brain regions involved in color perception, thus demonstrating their reality, and similarity to real color percepts, albeit evoked through a non-standard route.

Afterimages
After exposure to strong light in their sensitivity range, photoreceptors of a given type become desensitized. For a few seconds after the light ceases, they will continue to signal less strongly than they otherwise would. Colors observed during that period will appear to lack the color component detected by the desensitized photoreceptors. This effect is responsible for the phenomenon of afterimages, in which the eye may continue to see a bright figure after looking away from it, but in a complementary color.

Afterimage effects have also been utilized by artists, including Vincent van Gogh.

Color constancy
Main article: Color constancy
When an artist uses a limited color palette, the eye tends to compensate by seeing any gray or neutral color as the color which is missing from the color wheel. For example, in a limited palette consisting of red, yellow, black, and white, a mixture of yellow and black will appear as a variety of green, a mixture of red and black will appear as a variety of purple, and pure gray will appear bluish.[15]

The trichromatic theory is strictly true when the visual system is in a fixed state of adaptation. In reality, the visual system is constantly adapting to changes in the environment and compares the various colors in a scene to reduce the effects of the illumination. If a scene is illuminated with one light, and then with another, as long as the difference between the light sources stays within a reasonable range, the colors in the scene appear relatively constant to us. This was studied by Edwin Land in the 1970s and led to his retinex theory of color constancy.

Both phenomena are readily explained and mathematically modeled with modern theories of chromatic adaptation and color appearance (e.g. CIECAM02, iCAM).[16] There is no need to dismiss the trichromatic theory of vision, but rather it can be enhanced with an understanding of how the visual system adapts to changes in the viewing environment.

Color naming
Main article: Color term
See also: Lists of colors and Web colors

This picture contains one million pixels, each one a different color
Colors vary in several different ways, including hue (shades of red, orange, yellow, green, blue, and violet), saturation, brightness, and gloss. Some color words are derived from the name of an object of that color, such as "orange" or "salmon", while others are abstract, like "red".

In the 1969 study Basic Color Terms: Their Universality and Evolution, Brent Berlin and Paul Kay describe a pattern in naming "basic" colors (like "red" but not "red-orange" or "dark red" or "blood red", which are "shades" of red). All languages that have two "basic" color names distinguish dark/cool colors from bright/warm colors. The next colors to be distinguished are usually red and then yellow or green. All languages with six "basic" colors include black, white, red, green, blue, and yellow. The pattern holds up to a set of twelve: black, gray, white, pink, red, orange, yellow, green, blue, purple, brown, and azure (distinct from blue in Russian and Italian, but not English).

In culture
Colors, their meanings and associations can play major role in works of art, including literature.[17]

Associations
Individual colors have a variety of cultural associations such as national colors (in general described in individual color articles and color symbolism). The field of color psychology attempts to identify the effects of color on human emotion and activity. Chromotherapy is a form of alternative medicine attributed to various Eastern traditions. Colors have different associations in different countries and cultures.[18]

Different colors have been demonstrated to have effects on cognition. For example, researchers at the University of Linz in Austria demonstrated that the color red significantly decreases cognitive functioning in men.[19]

Spectral colors and color reproduction

The CIE 1931 color space chromaticity diagram. The outer curved boundary is the spectral (or monochromatic) locus, with wavelengths shown in nanometers. The colors depicted depend on the color space of the device on which you are viewing the image, and therefore may not be a strictly accurate representation of the color at a particular position, and especially not for monochromatic colors.
Most light sources are mixtures of various wavelengths of light. Many such sources can still effectively produce a spectral color, as the eye cannot distinguish them from single-wavelength sources. For example, most computer displays reproduce the spectral color orange as a combination of red and green light; it appears orange because the red and green are mixed in the right proportions to allow the eye's cones to respond the way they do to the spectral color orange.

A useful concept in understanding the perceived color of a non-monochromatic light source is the dominant wavelength, which identifies the single wavelength of light that produces a sensation most similar to the light source. Dominant wavelength is roughly akin to hue.

There are many color perceptions that by definition cannot be pure spectral colors due to desaturation or because they are purples (mixtures of red and violet light, from opposite ends of the spectrum). Some examples of necessarily non-spectral colors are the achromatic colors (black, gray, and white) and colors such as pink, tan, and magenta.

Two different light spectra that have the same effect on the three color receptors in the human eye will be perceived as the same color. They are metamers of that color. This is exemplified by the white light emitted by fluorescent lamps, which typically has a spectrum of a few narrow bands, while daylight has a continuous spectrum. The human eye cannot tell the difference between such light spectra just by looking into the light source, although reflected colors from objects can look different. (This is often exploited; for example, to make fruit or tomatoes look more intensely red.)

Similarly, most human color perceptions can be generated by a mixture of three colors called primaries. This is used to reproduce color scenes in photography, printing, television, and other media. There are a number of methods or color spaces for specifying a color in terms of three particular primary colors. Each method has its advantages and disadvantages depending on the particular application.

No mixture of colors, however, can produce a response truly identical to that of a spectral color, although one can get close, especially for the longer wavelengths, where the CIE 1931 color space chromaticity diagram has a nearly straight edge. For example, mixing green light (530 nm) and blue light (460 nm) produces cyan light that is slightly desaturated, because response of the red color receptor would be greater to the green and blue light in the mixture than it would be to a pure cyan light at 485 nm that has the same intensity as the mixture of blue and green.

Because of this, and because the primaries in color printing systems generally are not pure themselves, the colors reproduced are never perfectly saturated spectral colors, and so spectral colors cannot be matched exactly. However, natural scenes rarely contain fully saturated colors, thus such scenes can usually be approximated well by these systems. The range of colors that can be reproduced with a given color reproduction system is called the gamut. The CIE chromaticity diagram can be used to describe the gamut.

Another problem with color reproduction systems is connected with the acquisition devices, like cameras or scanners. The characteristics of the color sensors in the devices are often very far from the characteristics of the receptors in the human eye. In effect, acquisition of colors can be relatively poor if they have special, often very "jagged", spectra caused for example by unusual lighting of the photographed scene. A color reproduction system "tuned" to a human with normal color vision may give very inaccurate results for other observers.

The different color response of different devices can be problematic if not properly managed. For color information stored and transferred in digital form, color management techniques, such as those based on ICC profiles, can help to avoid distortions of the reproduced colors. Color management does not circumvent the gamut limitations of particular output devices, but can assist in finding good mapping of input colors into the gamut that can be reproduced.

Additive coloring

Additive color mixing: combining red and green yields yellow; combining all three primary colors together yields white.
Additive color is light created by mixing together light of two or more different colors. Red, green, and blue are the additive primary colors normally used in additive color systems such as projectors and computer terminals.

Subtractive coloring

Subtractive color mixing: combining yellow and magenta yields red; combining all three primary colors together yields black

Twelve main pigment colors
Subtractive coloring uses dyes, inks, pigments, or filters to absorb some wavelengths of light and not others. The color that a surface displays comes from the parts of the visible spectrum that are not absorbed and therefore remain visible. Without pigments or dye, fabric fibers, paint base and paper are usually made of particles that scatter white light (all colors) well in all directions. When a pigment or ink is added, wavelengths are absorbed or "subtracted" from white light, so light of another color reaches the eye.

If the light is not a pure white source (the case of nearly all forms of artificial lighting), the resulting spectrum will appear a slightly different color. Red paint, viewed under blue light, may appear black. Red paint is red because it scatters only the red components of the spectrum. If red paint is illuminated by blue light, it will be absorbed by the red paint, creating the appearance of a black object.

Structural color
Further information: Structural coloration and Animal coloration
Structural colors are colors caused by interference effects rather than by pigments. Color effects are produced when a material is scored with fine parallel lines, formed of one or more parallel thin layers, or otherwise composed of microstructures on the scale of the color's wavelength. If the microstructures are spaced randomly, light of shorter wavelengths will be scattered preferentially to produce Tyndall effect colors: the blue of the sky (Rayleigh scattering, caused by structures much smaller than the wavelength of light, in this case air molecules), the luster of opals, and the blue of human irises. If the microstructures are aligned in arrays, for example the array of pits in a CD, they behave as a diffraction grating: the grating reflects different wavelengths in different directions due to interference phenomena, separating mixed "white" light into light of different wavelengths. If the structure is one or more thin layers then it will reflect some wavelengths and transmit others, depending on the layers' thickness.

Structural color is studied in the field of thin-film optics. The most ordered or the most changeable structural colors are iridescent. Structural color is responsible for the blues and greens of the feathers of many birds (the blue jay, for example), as well as certain butterfly wings and beetle shells. Variations in the pattern's spacing often give rise to an iridescent effect, as seen in peacock feathers, soap bubbles, films of oil, and mother of pearl, because the reflected color depends upon the viewing angle. Numerous scientists have carried out research in butterfly wings and beetle shells, including Isaac Newton and Robert Hooke. Since 1942, electron micrography has been used, advancing the development of products that exploit structural color, such as "photonic" cosmetics.[20]

Additional terms
Color wheel: an illustrative organization of color hues in a circle that shows relationships.
Colorfulness, chroma, purity, or saturation: how "intense" or "concentrated" a color is. Technical definitions distinguish between colorfulness, chroma, and saturation as distinct perceptual attributes and include purity as a physical quantity. These terms, and others related to light and color are internationally agreed upon and published in the CIE Lighting Vocabulary.[21] More readily available texts on colorimetry also define and explain these terms.[16][22]
Dichromatism: a phenomenon where the hue is dependent on concentration and thickness of the absorbing substance.
Hue: the color's direction from white, for example in a color wheel or chromaticity diagram.
Shade: a color made darker by adding black.
Tint: a color made lighter by adding white.
Value, brightness, lightness, or luminosity: how light or dark a color is." (wikipedia.org)