Editing Indigo dye (section)

==History==
[[File:Indigo-Historische Farbstoffsammlung.jpg|thumb|right|Indigo, historical dye collection of the [[Dresden University of Technology|Technical University of Dresden]], Germany]]

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===Indigo versus woad===
[[File:Meisje met de parel.jpg|thumb|[[Johannes Vermeer]] used natural ultramarine in his paintings, as in his ''[[Girl with a Pearl Earring]]''. The expense was probably borne by his wealthy patron [[Pieter van Ruijven]].<ref>{{cite web |title=Girl with a Pearl Earring |url=http://www.essentialvermeer.com/catalogue/girl_with_a_pearl_earring.html |publisher=essentialvermeer.com |url-status=live |archive-url=https://web.archive.org/web/20150630060601/http://www.essentialvermeer.com/catalogue/girl_with_a_pearl_earring.html |archive-date=2015-06-30}}</ref>]]

In Europe, [[Isatis tinctoria]], or woad, had been the main source of [[indigo dye]], and the most readily-available source; the plant was processed into a paste called pastel. This industry was threatened in the 15th century by the arrival from India of the same dye ([[indigo]]), obtained from a shrub widely grown in Asia, ''[[Indigofera tinctoria]]''. The plant produced indigo dye in greater and more colourfast quantities than woad, making its introduction a major source of competition for European-produced indigo dye.

In 1498, [[Vasco da Gama]] opened a trade route to import indigo from India to Europe. In India, the indigo leaves were soaked in water, fermented, pressed into cakes, dried into bricks, then carried to the ports London, Marseille, Genoa, and Bruges.<ref name=autogenerated3>Eva Heller, ''Psychologie de la couleur effets et symboliques'' p. 21</ref> Later, in the 17th century, the British, Spanish, and Dutch established indigo plantations in Jamaica, South Carolina, the Virgin Islands and South America, and began to import American indigo to Europe. Countries with large and prosperous pastel industries attempted to block the import and use of indigo; one government in Germany outlawed the use of indigo in 1577, describing it as a "pernicious, deceitful and corrosive substance, the Devil's dye."<ref>[https://www.gutenberg.org/files/13242/13242-8.txt ''Lippincott's Magazine of Popular Literature and Science'', Volume 17, No. 100, April 1876] {{webarchive|url=https://web.archive.org/web/20121106154802/http://www.gutenberg.org/files/13242/13242-8.txt |date=2012-11-06}}.</ref><ref>D G Schreber, ''Historische, physische und economische Beschreibung des Waidtes'', 1752, the appendix; Thorpe JF and Ingold CK, 1923, ''Synthetic colouring matters – vat colours'' (London: Longmans, Green), p. 23</ref> In France, [[Henry IV of France|Henry IV]], in an edict of 1609, forbade under pain of death the use of "the false and pernicious Indian drug".<ref>{{cite book |last=Foucaud |first=Édouard |editor-last=Frost |editor-first=John |title=The book of illustrious mechanics of Europe and America |publisher=D. Appleton |year=1846 |page=[https://archive.org/details/bookillustrious00foucgoog/page/n246 236] |url=https://archive.org/details/bookillustrious00foucgoog}}</ref> It was forbidden in England until 1611, when British traders established their own indigo industry in India and began to import it into Europe.<ref name=autogenerated4>Eva Heller, ''Psychologie de la couleur – effets et symboliques'' p. 28</ref>

The efforts to block indigo were in vain; the quality of indigo blue was too high and the price too low for pastel made from woad to compete. In 1737, both the French and German governments finally allowed the use of indigo. This ruined the dye industries in Toulouse and the other cities that produced pastel, but created a thriving new indigo commerce to seaports such as Bordeaux, Nantes and Marseille.<ref>F. Lauterbach, ''Der Kampf des Waides mit dem Indigo'', Leipzig, p. 25. Cited by Michel Pastoureau, Bleu – Histoire d'une couleur, pp.&nbsp;108–13.</ref>

Another war of the blues took place at the end of the 19th century, between indigo and [[Baeyer–Drewson indigo synthesis|synthetic indigo]], discovered in 1868 by the German chemist Johann Friedrich Wilhelm Adolf von Baeyer. The German chemical firm [[BASF]] put the new dye on the market in 1897, in direct competition with the British-run indigo industry in India, which produced most of the world's indigo. In 1897 Britain sold ten thousand tons of natural indigo on the world market, while BASF sold six hundred tons of synthetic indigo. The British industry took measures to ensure their economic viability with the new BASF dye, but it was unable to compete; the synthetic indigo was more pure, made a more lasting blue, and was not dependent upon good or bad harvests. In 1911, India sold only 660 tons of natural indigo, while BASF sold 22,000 tons of synthetic indigo. In 2002, more than 38,000 tons of synthetic indigo was produced, often for the production of blue jeans.<ref name=Ullmann>{{Ullmann|first=Elmar|last=Steingruber|title=Indigo and Indigo Colorants|date=2004|doi=10.1002/14356007.a14_149.pub2}}</ref>

<gallery mode="packed" heights="150px">
File:Isatis tinctoria02.JPG|''[[Isatis tinctoria]]'', or woad, was the main source of blue dye in Europe from ancient times until the arrival of indigo from Asia and America. It was processed into a paste called pastel.
File:Schreber woad mill 1752.JPG|A woad mill in [[Thuringia]], in Germany, in 1752. The woad industry was already on its way to extinction, unable to compete with indigo blue.
File:The Hunt of the Unicorn Tapestry 1.jpg|A Dutch tapestry from 1495 to 1505. The blue colour comes from [[woad]].
File:Indigofera tinctoria1.jpg|''[[Indigofera tinctoria]]'', a tropical shrub, is the main source of indigo dye. The chemical composition of indigo dye is the same as that of woad, but the colour is more intense.
File:Indigo-Historische Farbstoffsammlung.jpg|Cakes of indigo. The leaf has been soaked in water, fermented, mixed with lye or another base, then pressed into cakes and dried, ready for export.
</gallery>
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The oldest known fabric dyed indigo, dated to 6,000 years ago, was discovered in [[Huaca Prieta]], Peru.<ref>{{cite journal |vauthors=Splitstoser JC, Dillehay TD, Wouters J, Claro A |date=2016-09-14 |title=Early pre-Hispanic use of indigo blue in Peru |journal=[[Science Advances]] |volume=2 |issue=9 |pages=e1501623 |doi=10.1126/sciadv.1501623 |pmid=27652337 |pmc=5023320 |bibcode=2016SciA....2E1623S}}</ref> Many Asian countries, such as [[India]], China, Japan, and [[Southeast Asia]]n nations have used indigo as a dye (particularly for [[silk]]) for centuries. The dye was also known to ancient civilizations in [[Mesopotamia]], [[ancient Egypt|Egypt]], [[prehistoric Britain|Britain]], [[Mesoamerica]], [[Peru]], [[Iran]], and [[West Africa]]. Indigo was also cultivated in India, which was also the earliest major center for its production and processing.<ref name=k&c>Kriger & Connah, page 120</ref> The ''[[Indigofera tinctoria]]'' species was domesticated in India.<ref name=k&c/> Indigo, used as a dye, made its way to the [[ancient Greece|Greeks]] and the [[ancient Rome|Romans]], where it was valued as a luxury product.<ref name=k&c/>

In Mesopotamia, a neo-Babylonian [[cuneiform]] tablet of the seventh century BC gives a recipe for the dyeing of wool, where [[Lapis lazuli|lapis]]-colored wool (''uqnatu'') is produced by repeated immersion and airing of the cloth.<ref name="StClair"/> Indigo was most probably imported from India. The Romans used indigo as a pigment for painting and for medicinal and cosmetic purposes. It was a luxury item imported to the Mediterranean from India by Arab merchants.

[[File:Indian indigo dye lump.jpg|thumb|Piece of indigo plant dye from India, {{circa|{{convert|2+1/2|cm|0}}}} square.]]
India was a primary supplier of indigo to Europe as early as the Greco-Roman era. The association of India with indigo is reflected in the Greek word for the dye, ''indikón'' ({{lang|grc|Ἰνδικόν}}, Indian).<ref name="StClair">{{cite book |title=The Secret Lives of Colour |last=St. Clair |first=Kassia |publisher=John Murray |year=2016 |isbn=9781473630819 |location=London |page=189 |oclc=936144129}}</ref> The Romans [[latin]]ized the term to ''indicum'', which passed into [[Venetian language|Italian dialect]] and eventually into English as the word indigo.

In [[Bengal Presidency|Bengal]] indigo cultivators revolted against exploitative working conditions created by European merchants and planters in what became known as the [[Indigo revolt]] in 1859. The Bengali play ''[[Nil Darpan]]'' by Indian playwright [[Dinabandhu Mitra]] was a fictionalized retelling of the revolt.

[[File:Ridpath's history of the world; being an account of the ethnic origin, primitive estate, early migrations, social conditions and present promise of the principal families of men (1897) (14597001160).jpg|thumb|Indigo factory at [[Allahabad]], India, drawn by {{Interlanguage link|Émile Thérond|fr|3=Émile Thérond}}, 19th century]]
The demand for indigo in the 19th century is indicated by the fact that in 1897, {{convert|7000|sqkm|sqmi|abbr=on}} were dedicated to the cultivation of indican-producing plants, mainly in [[India]]. By comparison, the country of [[Luxembourg]] is {{convert|2,586|sqkm|sqmi|abbr=on}}.<ref name=Ullmann/>

In Europe, indigo remained a rare commodity throughout the Middle Ages. A chemically identical dye derived from the woad plant ''([[Isatis tinctoria]])'' was used instead. In the late 15th century, the [[Portugal|Portuguese]] explorer [[Vasco da Gama]] discovered a sea route to India. This led to the establishment of direct trade with India, the [[Maluku Islands|Spice Islands]], China, and Japan. Importers could now avoid the heavy duties imposed by [[Iran|Persia]]n, [[Levant]]ine, and Greek middlemen and the lengthy and dangerous land routes which had previously been used. Consequently, the importation and use of indigo in Europe rose significantly. Much European indigo from Asia arrived through ports in Portugal, the Netherlands, and England. Many indigo plantations were established by European powers in tropical climates. Spain imported the dye from its colonies in Central and South America, and it was a major crop in [[Haiti]] and Jamaica, with much or all of the labor performed by enslaved Africans and African Americans. In the Spanish colonial era, intensive production of indigo for the world market in the region of modern El Salvador entailed such unhealthy conditions that the local indigenous population, forced to labor in pestilential conditions, was decimated.<ref>Fowler, Walter (6 August 1991). ''The Formation of Complex Society in Southeastern Mesoamerica''. CRC Press.</ref> Indigo plantations also thrived in the [[Virgin Islands]]. However, France and Germany outlawed imported indigo in the 16th century to protect the local woad dye industry. In central Europe, indigo resist dyeing is a centuries-old skill that has received UNESCO Intangible Cultural Heritage of Humanity recognition.<ref>{{cite web |last=Denisyuk |first=Yulia |title=Europe's secret dyeing formula |url=https://www.bbc.com/travel/article/20230420-blaudruck-europes-secret-dyeing-formula |access-date=2023-04-21 |website=bbc.com |language=en}}</ref>

[[Isaac Newton|Newton]] used "indigo" to describe one of the two new [[primary color]]s he added to the five he had originally named, in his revised account of the rainbow in ''Lectiones Opticae'' of 1675.<ref>Quoted in {{cite book |last=Hentschel |first=Klaus |title=Mapping the spectrum: techniques of visual representation in research and teaching |publisher=Oxford University Press |location=Oxford, England |year=2002 |page=28 |isbn=978-0-19-850953-0}}</ref>

Because of its high value as a trading commodity, indigo was often referred to as blue gold.<ref>{{cite web |title=History of Indigo & Indigo Dyeing |url=http://www.wildcolours.co.uk/html/indigo_history.html |website=wildcolours.co.uk |publisher=Wild Colours and natural Dyes |access-date=30 December 2015 |quote=Indigo was often referred to as Blue Gold as it was an ideal trading commodity; high value, compact and long lasting}}</ref>

In the early days of Islam, Christians were expected to wear a blue turban or mantle to identify them. In Egypt, which was majority [[Copts|Christian]] and remained so for generations, this created a high demand for blue dye, particularly indigo. Even though regulation of the distinguishing dress relaxed from the 10-16th centuries, indigo remained a significant part of the Egyptian economy. It lost its Christian connotations and became the color of the people's dress, because it was plentiful and cheap. It remained so until the 19th century. The British taxed farmers who grew indigo to encourage people to grow cotton, and restricted water use in favor of cotton. This also affected flax, which had been a popular local fiber for indigo dyers. This, paired with the import of cheap black cotton fabrics from Britain, caused blue to fall out of favor in Egyptian women's dress in the early 20th century. Egyptian men continued to wear indigo for some time, but the total preference for the dye waned as well.<ref name=":0">{{Cite book |last=Mehrez |first=Shahira |title=Costumes of Egypt: The Lost Legacies}}</ref> Blue was also a mourning color, and mourning women would dye their faces, arms, and hands blue for the week after the death and periodic grave visitations. Blue cloths were worn and waved around at these times as well to accompany the women's wailing.<ref name=":1">{{Cite book |last=Blackman |first=Winifred |title=The Fellahin of Upper Egypt}}</ref>

[[File:Touaregs at the Festival au Desert near Timbuktu, Mali 2012.jpg|thumb|[[Tuareg people|Tuaregs]] wearing the indigo-dyed [[tagelmust]]]]
Throughout West Africa, Indigo was the foundation of centuries-old textile traditions. From the [[Tuareg people|Tuareg]] nomads of the [[Sahara]] to [[Cameroon]], clothes dyed with indigo signified wealth. Women dyed the cloth in most areas, with the [[Yoruba people|Yoruba]] of [[Nigeria]] and the [[Mandinka people|Mandinka]] of [[Mali]] particularly well known for their expertise. Among the [[Hausa people|Hausa]] male dyers, working at communal dye pits was the basis of the wealth of the ancient city of [[Kano (city)|Kano]], and they can still be seen plying their trade today at the same pits.<ref>Kriger, Colleen E. & Connah, Graham (2006). ''Cloth in West African History''. Rowman Altamira. {{ISBN|0-7591-0422-0}}.</ref> The Tuareg are sometimes called the "Blue People" because the [[indigo]] pigment in the cloth of their traditional robes and turbans stained their skin dark blue.<ref name="GearonEamonn">Gearon, Eamonn, (2011) ''The Sahara: A Cultural History'' Oxford University Press, p. 239</ref>

Palestine and Iran also historically produced large amounts of indigo.<ref name=":0" /> In Palestine, it was a major industry since at least the 17th century. It was used to dye southern women's dresses, coats in Galilee, pants all over, and men's cloaks. A similar blue-to-black shift occurred due to British colonialism, though blue is still seen on traditional Palestinian dresses with some frequency in synthetic form. Widows would dye their dresses with indigo to cover the other colors, and wear blue veils and belts. Blue was also associated with unmarried girls, whose dresses were embroidered with it.<ref>{{Cite book |last=Weir |first=Shelagh |title=Palestinian Costume}}</ref>

[[File:Arimatsu Shibori手蜘蛛絞.jpg|thumb|Thread-tied {{transliteration|ja|[[shibori]]}} dying technique traditionally used in Japan; cloth ready for dyeing in indigo, and after dyeing]]
In Japan, indigo became especially important during the [[Edo period]]. This was due to a growing textiles industry,<ref name="Ikegami2005">{{cite book |author=Eiko Ikegami |title=Bonds of Civility: Aesthetic Networks and the Political Origins of Japanese Culture |url=https://books.google.com/books?id=KsN81J1s70kC&pg=PA284 |date=28 February 2005 |publisher=Cambridge University Press |isbn=978-0-521-60115-3 |page=284}}</ref> and because commoners had been banned from wearing silk,<ref name="Sagers2018">{{cite book |author=John H. Sagers |title=Confucian Capitalism: Shibusawa Eiichi, Business Ethics, and Economic Development in Meiji Japan |url=https://books.google.com/books?id=1-1lDwAAQBAJ&pg=PA27 |date=20 July 2018 |publisher=Springer |isbn=978-3-319-76372-9 |page=27}}</ref> leading to the increasing cultivation of cotton, and consequently indigo – one of the few substances that could dye it.<ref name="Wassenaar2011">{{cite book |author=Trudy M. Wassenaar |title=Bacteria: The Benign, the Bad, and the Beautiful |url=https://books.google.com/books?id=YGtR43I93iMC&pg=PA105 |date=3 November 2011 |publisher=John Wiley & Sons |isbn=978-1-118-14338-4 |page=105}}</ref>

In North America, indigo was introduced into colonial South Carolina by [[Eliza Lucas]], where it became the colony's second-most important cash crop (after rice).<ref>{{cite web |title=Eliza Lucas Pinckney: Indigo in the Atlantic World |author=Eliza Layne Martin |url=http://cwh.ucsc.edu/SocialBiog.Martin.pdf |access-date=2013-08-24 |url-status=dead |archive-url=https://web.archive.org/web/20100607061823/http://cwh.ucsc.edu/SocialBiog.Martin.pdf |archive-date=2010-06-07}}</ref> As a major export crop, indigo supported plantation slavery there.<ref>Andrea Feeser, ''Red, White, and Black Make Blue: Indigo in the Fabric of Colonial South Carolina Life'' (University of Georgia Press; 2013)</ref> In the May and June 1755 issues of ''[[The Gentleman's Magazine]],'' there appeared a detailed account of the cultivation of indigo, accompanied by drawings of necessary equipment and a prospective budget for starting such an operation, authored by South Carolina planter [[Charles Woodmason]]. It later appeared as a book.<ref>{{cite journal |last1=Jones |first1=Claude E. |year=1958 |title=Charles Woodmason as a Poet |journal=The South Carolina Historical Magazine |volume=59 |issue=4 |pages=189–194}}</ref><ref>{{cite book |last=Shields |first=David S. |title=Oracles of Empire: Poetry, Politics, and Commerce in British America, 1690-1750 |year=2010 |publisher=University of Chicago Press |pages=69, 249}}</ref> By 1775, indigo production in South Carolina exceeded 1,222,000 pounds.<ref>{{cite book |editor-last=Edgar |editor-first=Walter B. |title=The South Carolina Encyclopedia |year=2006 |publisher=University of South Carolina Press |page=9}}</ref> When [[Benjamin Franklin]] sailed to France in November 1776 to enlist France's support for the [[American Revolutionary War]], 35 barrels of indigo were on board the [[USS Reprisal (1776)|''Reprisal'']], the sale of which would help fund the war effort.<ref>{{cite book |last=Schoenbrun |first=David |date=1976 |title=Triumph in Paris: The Exploits of Benjamin Franklin |publisher=Harper & Row |location=New York |isbn=978-0-06-013854-7 |page=51}}</ref> In colonial North America, three commercially important species are found: the native ''I. caroliniana'', and the introduced ''I. tinctoria'' and ''I. suffruticosa''.<ref>{{cite journal |journal=Economic Botany |volume=33 |issue=2 |year=1979 |pages=128–134 |title=The indigo of commerce in colonial North America |author=David H. Rembert Jr. |doi=10.1007/BF02858281 |s2cid=2488865}}</ref>

===Synthetic development===
[[File:Indigoproduktion BASF 1890.JPG|thumb|Production of Indigo dye in a [[BASF]] plant (1890)]]
In 1865 the German chemist [[Adolf von Baeyer]] began working on the synthesis of indigo. He described his first synthesis of indigo in 1878 (from [[isatin]]) and a second synthesis in 1880 (from [[2-nitrobenzaldehyde]]). (It was not until 1883 that Baeyer finally determined the structure of indigo.<ref>Adolf Baeyer (1883) [https://gallica.bnf.fr/ark:/12148/bpt6k90697p/f512.image.langEN "Ueber die Verbindungen der Indigogruppe"] [On the compounds of the indigo group], ''Berichte der Deutschen chemischen Gesellschaft zu Berlin'', '''16''' : 2188-2204; see especially p. 2204.</ref>) The synthesis of indigo remained impractical, so the search for alternative starting materials at [[Badische Anilin- und Soda-Fabrik]] (BASF) and Hoechst continued. Johannes Pfleger<ref name="history.evonik.com">{{cite web |url=https://history.evonik.com/sites/geschichte/en/personalities/pfleger-johannes/pages/default.aspx |title=Johannes Pfleger - Das Evonik Geschichtsportal - Die Geschichte von Evonik Industries |website=history.evonik.com |access-date=7 June 2020 |archive-date=1 August 2020 |archive-url=https://web.archive.org/web/20200801202949/https://history.evonik.com/sites/geschichte/en/personalities/pfleger-johannes/pages/default.aspx |url-status=dead}}</ref> and [[:de:Karl Heumann|Karl Heumann]] eventually came up with industrial mass production synthesis.<ref name="ingenious.org.uk">{{cite web |url=http://www.ingenious.org.uk/site.asp?s=RM&Param=1&SubParam=1&Content=1&ArticleID=%7BCBDF1082-9F5C-498F-A769-B33A7DA83B30%7D&ArticleID2=%7B3C4444FC-FC4D-4498-B0B4-8B8A47C5BA76%7D&MenuLinkID=%7BA54FA022-17E2-483C-B937-DEC8B8964C33%7D |title=The Synthesis of Indigo |access-date=2015-01-05 |archive-url=https://web.archive.org/web/20160304084155/http://www.ingenious.org.uk/site.asp?s=RM&Param=1&SubParam=1&Content=1&ArticleID=%7BCBDF1082-9F5C-498F-A769-B33A7DA83B30%7D&ArticleID2=%7B3C4444FC-FC4D-4498-B0B4-8B8A47C5BA76%7D&MenuLinkID=%7BA54FA022-17E2-483C-B937-DEC8B8964C33%7D |archive-date=2016-03-04 |url-status=dead}}</ref>

The synthesis of N-(2-carboxyphenyl)glycine from the easy to obtain [[aniline]] provided a new and economically attractive route. BASF developed a commercially feasible manufacturing process that was in use by 1897, at which time 19,000 tons of indigo were being produced from plant sources. This had dropped to 1,000 tons by 1914 and continued to contract. By 2011, 50,000 tons of synthetic indigo were being produced worldwide.<ref>{{cite journal |title=Chemists go green to make better blue jeans |journal=Nature |year=2018 |volume=553 |issue=7687 |page=128 |doi=10.1038/d41586-018-00103-8 |bibcode=2018Natur.553..128. |doi-access=free}}</ref>