Editing Blue (section)

==Colourants==
{{Main|Colourants}}

<gallery mode="packed" heights="100px">
File:Egyptian blue.jpg|[[Egyptian blue]]
File:Cobalt Blue.JPG|[[Cobalt blue]]
File:Bleu phtalo.jpg|[[Copper phthalocyanine]]
File:YInMn_Blue_-_cropped.jpg|[[YInMn blue]]
File:Prussian blue.jpg|[[Prussian blue]], Fe{{su|p=III|b=4}}[Fe{{su|p=II}}([[Cyanide|CN]]){{su|b=6}}]{{su|b=3}}, is the blue of [[blueprint]]s.
</gallery>

===Artificial blues===
[[Egyptian blue]], the first artificial pigment, was produced in the third millennium BC in Ancient Egypt. It is produced by heating pulverized sand, copper, and [[natron]]. It was used in tomb paintings and funereal objects to protect the dead in their afterlife. Prior to the 1700s, blue colourants for artwork were mainly based on lapis lazuli and the related mineral ultramarine. A breakthrough occurred in 1709 when German druggist and pigment maker [[Johann Jacob Diesbach]] discovered [[Prussian blue]]. The new blue arose from experiments involving heating dried blood with iron sulphides and was initially called Berliner Blau. By 1710 it was being used by the French painter [[Antoine Watteau]], and later his successor [[Nicolas Lancret]]. It became immensely popular for the manufacture of wallpaper, and in the 19th century was widely used by French impressionist painters.<ref>Michel Pastoureau, ''Bleu – Histoire d'une couleur'', pp.&nbsp;114–16</ref> Beginning in the 1820s, Prussian blue was imported into Japan through the port of [[Nagasaki]]. It was called ''bero-ai'', or Berlin blue, and it became popular because it did not fade like traditional Japanese blue pigment, ''ai-gami'', made from the [[dayflower]]. Prussian blue was used by both [[Hokusai]], in his wave paintings, and [[Hiroshige]].<ref>Roger Keyes, ''Japanese Woodblock Prints: A Catalogue of the Mary A. Ainsworth Collection'', R, Allen Memorial Art Museum, Oberlin College, 1984, p. 42, plate #140, p. 91 and catalogue entry #439, p. 185. for more on the story of Prussian blue in Japanese prints, see also the website of the Victoria and Albert Museum, London.</ref>

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.<ref>Maerz and Paul (1930). ''A Dictionary of Color'' New York: McGraw Hill p. 206</ref>

In 1878 German chemists synthesized [[Indigo dye|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]].
<gallery mode="packed" heights="200px">
File:The Blue Boy.jpg|''[[The Blue Boy]]'' (1770), featuring lapis lazuli, indigo, and cobalt colourants,<ref>{{Cite web |title=Eight blue moments in art history |url=https://www.tate.org.uk/context-comment/blogs/eight-blue-moments-art-history  |archive-url=https://web.archive.org/web/20181016130010/https://www.tate.org.uk/context-comment/blogs/eight-blue-moments-art-history |archive-date=2018-10-16 |access-date=2018-10-16 |publisher=The Tate}}</ref>
File:Great Wave off Kanagawa2.jpg|''[[The Great Wave off Kanagawa]]'' illustrates the use of [[Prussian blue]]
File:Indigoproduktion BASF 1890.JPG|A synthetic indigo dye factory in Germany in 1890.
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===Dyes for textiles and food===
<ref name="Ag">{{Cite journal |last1=Newsome |first1=Andrew G. |last2=Culver |first2=Catherine A. |last3=Van Breemen |first3=Richard B. |year=2014 |title=Nature's Palette: The Search for Natural Blue Colorants |journal=Journal of Agricultural and Food Chemistry |volume=62 |issue=28 |pages=6498–6511 |doi=10.1021/jf501419q |pmid=24930897|bibcode=2014JAFC...62.6498N }}</ref> [[Woad]] and [[Indigofera tinctoria|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. Blue dyes are organic compounds, both synthetic and natural.

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.<ref name=Ag/>

Various [[raspberry]]-flavoured foods are dyed blue. This was done to distinguish [[strawberry]], [[watermelon]] and [[raspberry]]-flavoured foods.<ref>{{Cite web |date=2023-06-21 |title=You Need To Know The Truth About Blue Raspberry |url=https://www.delish.com/food-news/a44272957/what-is-blue-raspberry/ |access-date=2024-10-22 |website=Delish |language=en-US}}</ref>  The company [[The Icee Company|ICEE]] used Blue No. 1 for their blue raspberry ICEEs. 

<gallery mode="packed" heights="150px">
File:Blue Raspberry Frozen Yogurt with White Chocolate Chips, Coconut, and Cherries.jpg|Blue Raspberry Frozen Yogurt with White Chocolate Chips, Coconut, and Cherries.
File:Blue haribo jelly beans.jpg|Blue haribo jelly beans. Raspberry flavour. Bought in the UK.
File:2019-11-09 19 29 30 A blue raspberry-flavored Jolly Rancher Hard Candy Stix after being unwrapped in the Dulles section of Sterling, Loudoun County, Virginia.jpg|A blue raspberry-flavoured Jolly Rancher Hard Candy Stix after being unwrapped in the Dulles section of Sterling, Loudoun County, Virginia.
File:Indigo skeletal.svg|Chemical structure of [[indigo dye]], a widely produced blue dye. [[jeans|Blue jeans]] consist of 1–3% by weight of this [[organic compound]].
File:C.I. Acid Blue 9.svg|upright=1.15|Chemical structure of C.I. Acid Blue 9, a dye commonly used in candies.
</gallery>

=== Pigments for painting and glass ===
{{See also|Blue pigments}}
{{Anchor|main pigment}}Blue [[pigment]]s 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|tempera painting]]); or with a slow-drying oil, such as [[linseed oil]], for [[oil painting]]. Two inorganic but synthetic blue pigments are [[cerulean|cerulean blue]] (primarily cobalt(II) stanate: {{chem2|Co2SnO4}}) and [[Prussian blue]] (milori blue: primarily {{chem2|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.<ref>{{Cite book |last1=Placke |first1=Mina |title=Ullmann's Encyclopedia of Industrial Chemistry |last2=Fischer |first2=Norbert |last3=Colditz |first3=Michael |last4=Kunkel |first4=Ernst |last5=Bohne |first5=Karl-Heinz |year=2016 |isbn=978-3-527-30673-2 |pages=1–12 |chapter=Drawing and Writing Materials |doi=10.1002/14356007.a09_037.pub2}}</ref> [[Blueprint]]ing involves the production of [[Prussian blue]] in situ.

===Inorganic compounds===
{{multiple image
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| image1            = Copper sulfate.jpg
 | alt1              = 
 | caption1          = CuSO<sub>4</sub><sup>.</sup>5H<sub>2</sub>O

| image2            = Cobaltous chloride anhydrous.jpg
 | alt2              = 
 | caption2          = [[Anhydrous]] cobalt(II) chloride

| image3            = Vanadyl sulfate.jpg
 | caption3          = [[Vanadyl sulfate]]
}}
Certain metal [[ion]]s characteristically form blue solutions or blue salts. Of some practical importance, [[cobalt]] is used to make the deep blue glazes and glasses. It substitutes for [[silicon]] or [[Aluminium|aluminum]] ions in these materials. Cobalt is the blue [[chromophore]] in [[Stained glass|stained glass windows]], such as those in [[Gothic cathedrals and churches|Gothic cathedrals]] and in Chinese [[porcelain]] beginning in the [[Tang dynasty]]. [[Copper#Compounds|Copper(II)]] (Cu<sup>2+</sup>) also produces many blue compounds, including the commercial [[Algaecide|algicide]] [[copper(II) sulfate]] (CuSO<sub>4</sub><sup>.</sup>5H<sub>2</sub>O). Similarly, [[Vanadyl ion|vanadyl]] salts and solutions are often blue, e.g. [[vanadyl sulfate]].