Blue

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Blue
 
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Blue is one of the three

visible light. The term blue generally describes colours perceived by humans observing light with a dominant wavelength between approximately 450 and 495 nanometres. Most blues contain a slight mixture of other colours; azure contains some green, while ultramarine contains some violet. The clear daytime sky and the deep sea appear blue because of an optical effect known as Rayleigh scattering. An optical effect called the Tyndall effect explains blue eyes. Distant objects appear more blue because of another optical effect called aerial perspective
.

Blue has been an important colour in art and decoration since ancient times. The semi-precious stone

woad until it was replaced by the finer indigo from America. In the 19th century, synthetic blue dyes and pigments gradually replaced organic dyes and mineral pigments. Dark blue became a common colour for military uniforms and later, in the late 20th century, for business suits. Because blue has commonly been associated with harmony, it was chosen as the colour of the flags of the United Nations and the European Union.[4]

In the United States and Europe, blue is the colour that both men and women are most likely to choose as their favourite, with at least one recent survey showing the same across several other countries, including China, Malaysia, and Indonesia.[5][6] Past surveys in the US and Europe have found that blue is the colour most commonly associated with harmony, confidence, masculinity, knowledge, intelligence, calm, distance, infinity, the imagination, cold, and sadness.[7]

Etymology and linguistics

The modern English word blue comes from Middle English bleu or blewe, from the Old French bleu, a word of Germanic origin, related to the Old High German word blao (meaning 'shimmering, lustrous').[8] In heraldry, the word azure is used for blue.[9]

In

Colour term
.

Several languages, including

traffic signal meaning "go". In Lakota, the word tȟó is used for both blue and green, the two colours not being distinguished in older Lakota. (For more on this subject, see Blue–green distinction in language
.)

Linguistic research indicates that languages do not begin by having a word for the colour blue.[11] Colour names often developed individually in natural languages, typically beginning with black and white (or dark and light), and then adding red, and only much later – usually as the last main category of colour accepted in a language – adding the colour blue, probably when blue pigments could be manufactured reliably in the culture using that language.[11]

Optics and colour theory

The term blue generally describes colours perceived by humans observing light with a dominant wavelength between approximately 450 and 495 nanometres.[12] Blues with a higher frequency and thus a shorter wavelength gradually look more violet, while those with a lower frequency and a longer wavelength gradually appear more green. Purer blues are in the middle of this range, e.g., around 470 nanometres.

Isaac Newton included blue as one of the seven colours in his first description of the visible spectrum.[13] He chose seven colours because that was the number of notes in the musical scale, which he believed was related to the optical spectrum. He included indigo, the hue between blue and violet, as one of the separate colours, though today it is usually considered a hue of blue.[14]

In painting and traditional

RYB colour model
.)

The RYB model was used for

colour printing by Jacob Christoph Le Blon as early as 1725. Later, printers discovered that more accurate colours could be created by using combinations of cyan, magenta, yellow, and black ink, put onto separate inked plates and then overlaid one at a time onto paper. This method could produce almost all the colours in the spectrum
with reasonable accuracy.

  • Additive colour mixing. The combination of primary colours produces secondary colours where two overlap; the combination red, green, and blue each in full intensity makes white.
    Additive colour mixing. The combination of
    primary colours
    produces secondary colours where two overlap; the combination red, green, and blue each in full intensity makes white.
  • Red, green, and blue subpixels on an LCD display.
    Red, green, and blue
    LCD display
    .

On the

RYB) where blue was considered a primary colour, its complementary colour is considered to be orange (based on the Munsell colour wheel).[15]

LED

In 1993, high-brightness blue LEDs were demonstrated by

Nichia Corporation.[16][17][18] In parallel, Isamu Akasaki and Hiroshi Amano of Nagoya University were working on a new development which revolutionized LED lighting.[19][20]

Nakamura was awarded the 2006 Millennium Technology Prize for his invention.[21] Nakamura, Hiroshi Amano and Isamu Akasaki were awarded the Nobel Prize in Physics in 2014 for the invention of an efficient blue LED.[22]

Lasers

DPSS which are comparatively expensive and inefficient, but still widely used by scientists for applications including optogenetics, Raman spectroscopy, and particle image velocimetry, due to their superior beam quality.[24] Blue gas lasers are also still commonly used for holography, DNA sequencing, optical pumping
, among other scientific and medical applications.

Shades and variations

Various shades of blue

Blue is the colour of light between violet and cyan on the visible spectrum. Hues of blue include indigo and ultramarine, closer to violet; pure blue, without any mixture of other colours; Azure, which is a lighter shade of blue, similar to the colour of the sky; Cyan, which is midway in the spectrum between blue and green, and the other blue-greens such as turquoise, teal, and aquamarine.

Blue also varies in shade or tint; darker shades of blue contain black or grey, while lighter tints contain white. Darker shades of blue include ultramarine,

List of colours
).

As a structural colour

In nature, many blue phenomena arise from

thin films, combined with refraction as light enters and exits such films. The geometry then determines that at certain angles, the light reflected from both surfaces interferes constructively, while at other angles, the light interferes destructively. Diverse colours therefore appear despite the absence of colourants.[25]

Colourants

Artificial blues

dayflower. Prussian blue was used by both Hokusai, in his wave paintings, and Hiroshige.[27]

In 1799 a French chemist, Louis Jacques Thénard, made a synthetic cobalt blue pigment which became immensely popular with painters.

In 1824 the

Societé pour l'Encouragement d'Industrie in France offered a prize for the invention of an artificial ultramarine which could rival the natural colour made from lapis lazuli. The prize was won in 1826 by a chemist named Jean Baptiste Guimet, but he refused to reveal the formula of his colour. In 1828, another scientist, Christian Gmelin then a professor of chemistry in Tübingen, found the process and published his formula. This was the beginning of new industry to manufacture artificial ultramarine, which eventually almost completely replaced the natural product.[28]

In 1878 German chemists synthesized indigo. This product rapidly replaced natural indigo, wiping out vast farms growing indigo. It is now the blue of blue jeans. As the pace of organic chemistry accelerated, a succession of synthetic blue dyes were discovered including Indanthrone blue, which had even greater resistance to fading during washing or in the sun, and copper phthalocyanine.

Dyes for textiles and food

Chemical structure of indigo dye, a widely produced blue dye. Blue jeans consist of 1–3% by weight of this organic compound.
Chemical structure of C.I. Acid Blue 9, a dye commonly used in candies.

Blue dyes are organic compounds, both synthetic and natural.

Woad and true indigo
were once used but since the early 1900s, all indigo is synthetic. Produced on an industrial scale, indigo is the blue of blue jeans.

For food, the triarylmethane dye Brilliant blue FCF is used for candies. The search continues for stable, natural blue dyes suitable for the food industry.[30]

Pigments for painting and glass

Blue pigments were once produced from minerals, especially lapis lazuli and its close relative ultramarine. These minerals were crushed, ground into powder, and then mixed with a quick-drying binding agent, such as egg yolk (tempera painting); or with a slow-drying oil, such as linseed oil, for oil painting. Two inorganic but synthetic blue pigments are cerulean blue (primarily cobalt(II) stanate: Co2SnO4) and Prussian blue (milori blue: primarily Fe7(CN)18). The chromophore in blue glass and glazes is cobalt(II). Diverse cobalt(II) salts such as cobalt carbonate or cobalt(II) aluminate are mixed with the silica prior to firing. The cobalt occupies sites otherwise filled with silicon.

Inks

Methyl blue is the dominant blue pigment in inks used in pens.[31] Blueprinting involves the production of Prussian blue in situ.

Inorganic compounds

CuSO4.5H2O
Anhydrous cobalt(II) chloride

Certain metal

Tang Dynasty. Copper(II) (Cu2+) also produces many blue compounds, including the commercial algicide copper(II) sulfate (CuSO4.5H2O). Similarly, vanadyl salts and solutions are often blue, e.g. vanadyl sulfate
.

In nature

Sky and sea

When sunlight passes through the atmosphere, the blue wavelengths are scattered more widely by the oxygen and nitrogen molecules, and more blue comes to our eyes. This effect is called

Lord Rayleigh and confirmed by Albert Einstein in 1911.[32][33]

The sea is seen as blue for largely the same reason: the water absorbs the longer wavelengths of red and reflects and scatters the blue, which comes to the eye of the viewer. The deeper the observer goes, the darker the blue becomes. In the open sea, only about one per cent of light penetrates to a depth of 200 metres. (See

euphotic depth
)

The colour of the sea is also affected by the colour of the sky, reflected by particles in the water; and by algae and plant life in the water, which can make it look green; or by sediment, which can make it look brown.[34]

The farther away an object is, the more blue it often appears to the eye. For example, mountains in the distance often appear blue. This is the effect of

atmospheric perspective; the farther an object is away from the viewer, the less contrast there is between the object and its background colour, which is usually blue. In a painting where different parts of the composition are blue, green and red, the blue will appear to be more distant, and the red closer to the viewer. The cooler a colour is, the more distant it seems.[35] Blue light is scattered more than other wavelengths by the gases in the atmosphere
, hence our "blue planet".


Minerals

  • Lapis-lazuli
    Lapis-lazuli
  • Azurite
  • Natural ultramarine pigment
    Natural ultramarine pigment
  • Logan sapphire
    Logan sapphire

Some of the most desirable gems are blue, including sapphire and tanzanite. Compounds of copper(II) are characteristically blue and so are many copper-containing minerals.

Virgin Mary
.

Plants and fungi

Intense efforts have focused on blue flowers and the possibility that natural blue colourants could be used as food dyes.[30] Commonly, blue colours in plants are anthocyanins: "the largest group of water-soluble pigments found widespread in the plant kingdom."[37] In the few plants that exploit structural colouration, brilliant colours are produced by structures within cells. The most brilliant blue colouration known in any living tissue is found in the marble berries of Pollia condensata, where a spiral structure of cellulose fibrils scattering blue light. The fruit of quandong (Santalum acuminatum) can appear blue owing to the same effect.[30]

Animals

Blue-pigmented animals are relatively rare.

morpho butterfly,[43] collagen fibres in the skin of some species of monkey and opossum,[44] and the iridophore cells in some fish and frogs.[45][46]

Eyes

Blue eyes actually contain no blue pigment. The colour is caused by an effect called Tyndall scattering.

Blue eyes do not actually contain any blue pigment.

Eye colour is determined by two factors: the pigmentation of the eye's iris[47][48] and the scattering of light by the turbid medium in the stroma of the iris.[49] In humans, the pigmentation of the iris varies from light brown to black. The appearance of blue, green, and hazel eyes results from the Tyndall scattering of light in the stroma, an optical effect similar to what accounts for the blueness of the sky.[49][50] The irises of the eyes of people with blue eyes contain less dark melanin
than those of people with brown eyes, which means that they absorb less short-wavelength blue light, which is instead reflected out to the viewer. Eye colour also varies depending on the lighting conditions, especially for lighter-coloured eyes.

Blue eyes are most common in Ireland, the Baltic Sea area and Northern Europe,[51] and are also found in Eastern, Central, and Southern Europe. Blue eyes are also found in parts of Western Asia, most notably in Afghanistan, Syria, Iraq, and Iran.[52] In Estonia, 99% of people have blue eyes.[53][54] In Denmark in 1978, only 8% of the population had brown eyes, though through immigration, today that number is about 11%.[54] In Germany, about 75% have blue eyes.[54]

In the United States, as of 2006, one out of every six people, or 16.6% of the total population, and 22.3% of the white population, have blue eyes, compared with about half of Americans born in 1900, and a third of Americans born in 1950. Blue eyes are becoming less common among American children[citation needed]. In the US, boys are 3–5 per cent more likely to have blue eyes than girls.[51]

History

In the ancient world

  • Lapis lazuli bowl from Iran, end of 3rd – beginning of 2nd millennium BC (Louvre Museum)
    Lapis lazuli bowl from Iran, end of 3rd – beginning of 2nd millennium BC (Louvre Museum)
  • Egyptian blue tripodic beaker imitating lapis lazuli. South Mesopotamia. (1399-1200 BC)
    Egyptian blue tripodic beaker imitating lapis lazuli. South Mesopotamia. (1399-1200 BC)
  • Fresco of Polyphemus and Galatea, Pompei, using Egyptian blue (1st c. BC) (Metropolitan Museum)
    Fresco of Polyphemus and Galatea, Pompei, using Egyptian blue (1st c. BC) (Metropolitan Museum)

As early as the 7th millennium BC, lapis lazuli was mined in the Sar-i Sang mines,[55] in Shortugai, and in other mines in Badakhshan province in northeast Afghanistan.[56]

Lapis lazuli artifacts, dated to 7570 BC, have been found at

funeral mask of Tutankhamun (1341–1323 BC).[61]

A term for Blue was relatively rare in many forms of ancient art and decoration, and even in ancient literature. The Ancient Greek poets described the sea as green, brown or "the colour of wine". The colour is mentioned several times in the Hebrew Bible as 'tekhelet'. Reds, blacks, browns, and ochres are found in cave paintings from the Upper Paleolithic period, but not blue. Blue was also not used for dyeing fabric until long after red, ochre, pink, and purple. This is probably due to the perennial difficulty of making blue dyes and pigments. On the other hand, the rarity of blue pigment made it even more valuable.[62]

The earliest known blue dyes were made from plants –

woad in Europe, indigo in Asia and Africa, while blue pigments were made from minerals, usually either lapis lazuli or azurite, and required more.[63] Blue glazes posed still another challenge since the early blue dyes and pigments were not thermally robust. In c. 2500 BC, the blue glaze Egyptian blue was introduced for ceramics, as well as many other objects.[64][65] The Greeks imported indigo dye from India, calling it indikon, and they painted with Egyptian blue. Blue was not one of the four primary colours for Greek painting described by Pliny the Elder (red, yellow, black, and white). For the Romans, blue was the colour of mourning, as well as the colour of barbarians. The Celts and Germans reportedly dyed their faces blue to frighten their enemies, and tinted their hair blue when they grew old.[66] The Romans made extensive use of indigo and Egyptian blue pigment, as evidenced, in part, by frescos in Pompeii
. The Romans had many words for varieties of blue, including caeruleus, caesius, glaucus, cyaneus, lividus, venetus, aerius, and ferreus, but two words, both of foreign origin, became the most enduring; blavus, from the Germanic word blau, which eventually became bleu or blue; and azureus, from the Arabic word lazaward, which became azure.[67]

Blue was widely used in the decoration of churches in the Byzantine Empire.[68] By contrast, in the Islamic world, blue was of secondary to green, believed to be the favourite colour of the Prophet Mohammed. At certain times in Moorish Spain and other parts of the Islamic world, blue was the colour worn by Christians and Jews, because only Muslims were allowed to wear white and green.[69]

In the Middle Ages

  • Stained glass window at Saint Denis Basilica (1130-1140), coloured with cobalt blue
    Stained glass window at
    Saint Denis Basilica (1130-1140), coloured with cobalt blue
  • Detail of the Blue Virgin Window, Chartres Cathedral (12th c.)
    Detail of the Blue Virgin Window, Chartres Cathedral (12th c.)
  • The Wilton Diptych (1395–1399). The Virgin Mary was traditionally shown in blue(14th c.)
    The
    Virgin Mary
    was traditionally shown in blue(14th c.)

In the art and life of Europe during the early

Christian world, and the colour became known as the "bleu de Saint-Denis". In the years that followed even more elegant blue stained glass windows were installed in other churches, including at Chartres Cathedral and Sainte-Chapelle in Paris.[71]

In the 12th century the Roman Catholic Church dictated that painters in Italy (and the rest of Europe consequently) to paint the Virgin Mary with blue, which became associated with holiness, humility and virtue. In medieval paintings, blue was used to attract the attention of the viewer to the Virgin Mary. Paintings of the mythical King Arthur began to show him dressed in blue. The coat of arms of the kings of France became an azure or light blue shield, sprinkled with golden fleur-de-lis or lilies. Blue had come from obscurity to become the royal colour.[72]

Renaissance through 18th century

Blue came into wider use beginning in the Renaissance, when artists began to paint the world with perspective, depth, shadows, and light from a single source. In Renaissance paintings, artists tried to create harmonies between blue and red, lightening the blue with lead white paint and adding shadows and highlights. Raphael was a master of this technique, carefully balancing the reds and the blues so no one colour dominated the picture.[73]

Ultramarine was the most prestigious blue of the Renaissance, being more expensive than gold. Wealthy art patrons commissioned works with the most expensive blues possible. In 1616 Richard Sackville commissioned a portrait of himself by Isaac Oliver with three different blues, including ultramarine pigment for his stockings.[74]

  • Portrait of Richard Sackville (1616), using three expensive blues, including ultramarine for his stockings
    Portrait of Richard Sackville (1616), using three expensive blues, including ultramarine for his stockings
  • Ming Dynasty, Porcelain vase painted with cobalt blue under transparent glaze. (15th c.) (Metropolitan Museum)
    Ming Dynasty, Porcelain vase painted with cobalt blue under transparent glaze. (15th c.) (Metropolitan Museum)
  • Delftware plaque with cobalt blue painting (1683) (Rijksmuseum, Amsterdam)
    Delftware plaque with cobalt blue painting (1683) (Rijksmuseum, Amsterdam)
  • Portrait of King Louis XIV of France in coronation robes, by Hyacinthe Rigaud (c. 1700) (Louvre Museum)
    Portrait of King
    Louis XIV of France in coronation robes, by Hyacinthe Rigaud
    (c. 1700) (Louvre Museum)
  • Urn by Josiah Wedgewood (1780s) (Metropolitan Museum)
    Urn by
    Josiah Wedgewood
    (1780s) (Metropolitan Museum)
  • Queen Maria I of Portugal (late 1700s)
    Queen Maria I of Portugal (late 1700s)
  • "Girl with a Pearl Earring" by Johannes Vermeer features ultramarine pigment
    "Girl with a Pearl Earring" by Johannes Vermeer features ultramarine pigment

An industry for the manufacture of fine blue and white pottery began in the 14th century in Jingdezhen, China, using white Chinese porcelain decorated with patterns of cobalt blue, imported from Persia. It was first made for the family of the Emperor of China, then was exported around the world, with designs for export adapted to European subjects and tastes. The Chinese blue style was also adapted by Dutch craftsmen in Delft and English craftsmen in Staffordshire in the 17th-18th centuries. in the 18th century, blue and white porcelains were produced by Josiah Wedgwood and other British craftsmen.[75]

19th-20th century

The early 19th century saw the ancestor of the modern blue business suit, created by

blue jeans, a highly popular form of workers's costume, invented in 1853 by Jacob W. Davis who used metal rivets to strengthen blue denim work clothing in the California gold fields. The invention was funded by San Francisco entrepreneur Levi Strauss, and spread around the world.[76]

Recognizing the emotional power of blue, many artists made it the central element of paintings in the 19th and 20th centuries. They included

abstract expressionist movement use blues to inspire ideas and emotions. Painter Mark Rothko observed that colour was "only an instrument;" his interest was "in expressing human emotions tragedy, ecstasy, doom, and so on."[79]

In society and culture

Uniforms

In the 17th century. The Prince-Elector of Brandenburg,

Woad, a local crop, rather than Indigo, which was produced by the colonies of Brandenburg's rival, England. It was worn by the German army until World War I, with the exception of the soldiers of Bavaria, who wore sky-blue.[80]

In 1748, the

Whig Party. Blue continued to be the colour of the field uniform of the US Army until 1902, and is still the colour of the dress uniform.[82]

In the 19th century, police in the United Kingdom, including the Metropolitan Police and the City of London Police also adopted a navy blue uniform. Similar traditions were embraced in France and Austria.[83] It was also adopted at about the same time for the uniforms of the officers of the New York City Police Department.[76]

Religion

  • In Hinduism, Krishna is depicted with blue skin
    In Hinduism, Krishna is depicted with blue skin
  • Blue domes of the Church dedicated to St. Spirou in Firostefani, Santorini island (Thira), Greece.
    Blue domes of the Church dedicated to St. Spirou in Firostefani, Santorini island (Thira), Greece.
  • Persian blue in Shah mosque (16th c.) in Isfahan, Iran
    Persian blue in
    Shah mosque (16th c.) in Isfahan
    , Iran
  • The flag of Israel uses a special variety of blue, called tekhelet
    The flag of Israel uses a special variety of blue, called tekhelet
  • menorah, many of the vessels, and the Ark of the Covenant, were covered with blue cloth when transported from place to place.[89]
  • Blue in
    Virgin Mary. This was the result of a decree of Pope Gregory I (540-601) who ordered that all religious paintings should tell a story which was clearly comprehensible to all viewers, and that figures should be easily recognizable, especially that of the figure of Mary. If she was alone in the image, her costume was usually painted with the finest blue, ultramarine. If she was with Christ, her costume was usually painted with a less expensive pigment, to avoid outshining him.[90][91][92][93]
  • Blue in Hinduism: Many of the gods are depicted as having blue-coloured skin, particularly those associated with Vishnu, who is said to be the preserver of the world, and thus intimately connected to water. Krishna and Rama, Vishnu's avatars, are usually depicted with blue skin. Shiva, the destroyer deity, is also depicted in a light-blue hue, and is called neela kantha, or blue-throated, for having swallowed poison to save the universe during the Samudra Manthana, the churning of the ocean of milk. Blue is used to symbolically represent the fifth, and the throat, chakra (Vishuddha).[94]
  • Blue in Sikhism: The Akali Nihangs warriors wear all-blue attire. Guru Gobind Singh also has a blue roan horse. The Sikh Rehat Maryada states that the Nishan Sahib hoisted outside every Gurudwara should be xanthic (Basanti in Punjabi) or greyish blue (modern day navy blue) (Surmaaee in Punjabi) colour.[95][96]
  • Blue in Paganism: Blue is associated with peace, truth, wisdom, protection, and patience. It helps with healing, psychic ability, harmony, and understanding.[97]

Sports

In sports, blue is widely represented in uniforms in part because the majority of national teams wear the colours of their national flag. For example, the national men's football team of

One day international matches, as such the team is also referred to as "Men in Blue".[99]

Politics

  • Flag of the United Nations, approximates "sky blue"
    Flag of the United Nations, approximates "sky blue"
  • Flag of the European Union is "reflex blue", a medium dark blue
    Flag of the European Union is "reflex blue", a medium dark blue
  • A presidential-election map of the US, 2008–2020. States that consistently vote for Democrats are termed "blue states".
    A presidential-election map of the US, 2008–2020. States that consistently vote for Democrats are termed "blue states".

Unlike red or green, blue was not strongly associated with any particular country, religion or political movement. As the colour of harmony, it was chosen as the colour for the flags of the United Nations, the European Union, and NATO.[100] In politics, blue is often used as the colour of conservative parties, contrasting with the red associated with left-wing parties.[101] Some conservative parties that use the colour blue include the Conservative Party (UK),[102] Conservative Party of Canada,[103] Liberal Party of Australia,[104] Liberal Party of Brazil, and Likud of Israel. In some countries, however, like the United States, the colours are reversed. To avoid associations of the Democrats with socialism or the far left, U.S. states which voted Democratic in four consecutive presidential elections are termed "blue states", while those which voted for Republicans are termed "red states".[105] States which voted for different parties in two of the last four presidential elections are called "swing states", and are usually coloured purple, a mix of red and blue, or sometimes pink or light blue.[106]South Korea also uses this colour model, with the Democratic Party on the left using blue[107] and the People Power Party on the right using red.

See also

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Works cited

Further reading

External links