INDIGO /ˈɪndɪɡəʊ/

A variety of plants have provided indigo throughout history, but most natural indigo is obtained from those in the genus Indigofera, which are native to the tropics. In temperate climates indigo can also be obtained from woad (Isatis tinctoria) and dyer's knotweed (Polygonum tinctorum).
The primary commercial indigo species in Asia was true indigo (Indigofera tinctoria, also known as Indigofera sumatrana). In Central and South America the two species Indigofera suffruticosa (Anil) and Indigofera arrecta (Natal indigo) were the most important.
The plants of the genus Indigofera produce a much stronger dye than those of the Isatis (woad) family; however, dyer’s woad is much more easily cultivated and therefore more widely used than Indigofera, which needs a tropical climate. Isatis tinctoria grows up to approximately 1.50 m(5’) in height and can be harvested three times a year

Indigofera tinctoria
Preparation of indigo dye with Indigofera tinctoria
After the field has been ploughed, the seeds are planted at the beginning of the rainy season and are ready to harvest in 4 months. Indigo plant is suitable to grow in areas not subject to flooding, for example, in the back yard of the house or the area around the shelter where cows and buffaloes are kept. The high land near the rice paddy is also suitable for growing this indigo plant. Little care is needed for young plants. All that is needed is to keep weeds away from the young plants until they grow 1 foot high, and then keep the cows and buffaloes from destroying the indigo plant before harvesting.
Four months after planting the seeds the leaves of the indigo plant start turning dark green which indicates good quality dye. The plants are cut off and made into small bundles.
The leaves are then soaked in a large earthenware jar filled with water and left to be fermented in order to convert the glycoside indican which is naturally present in the plant to the blue dye indigotin. The precipitate from the fermented leaf solution is mixed with a strong base such as lye, pressed into cakes, dried, and powdered. The powder is then mixed with various other substances to produce different shades of blue and purple.

In History
The name indigo comes from the Roman term indicum, which means a product of India. This is somewhat of a misnomer since the plant is grown in many areas of the world, including Asia, Java, Japan, and Central America. Another ancient term for the dye is nil from which the Arabic term for blue, al-nil, is derived. The English word aniline comes from the same source.
The color indigo, often associated with political power or religious ritual, has held a significant place in many world civilizations such as Mesopotamia, Egypt, Greece, Rome, Mesoamerica, Iran, and Africa for thousands of years. In the excavation of Thebes an indigo garment dating from c. 2500 B.C. was found, for example — furthermore, the Hindu god Krishna is most often depicted in blue, human sacrifices were often painted blue in ancient Mayan culture, and the Virgin Mary is regularly imagined draped in blue clothes in Christian art.
In Mesopotamia, a Neo-Babylonian cuneiform tablet of the 7th century BC gives a recipe for the dyeing of wool, where lapis-colored wool (uqnatu) is produced by repeated immersion and airing of the cloth.
The dye is first mentioned in a written source for Western Europe in the histories of Herodotus (writing around 450 B.C.), who described its use in the Mediterranean area. 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. Indigo plant used to be planted in Khuzestan and other southern regions of Iran too. It was at the time of the Crusades, however, that indigo became one of the valued “spices” that Italian merchants acquired in Cyprus, Alexandria and Baghdad. These cities were themselves end-points for caravans from the Far East. But the trade in indigo dye only became a commercial force after 1498 with the opening of the sea route to India. This is not to say that Europeans had no other way of obtaining deep blue dye. The woad plant, native to northern Italy, southern France, and parts of England and Germany, yielded indigo-colored dye from its leaves, but it was inferior to that obtained from the indigo plant. Quite naturally, the woad-growers of Europe (both peasants and princes) sought to protect their industry against the influx of affordable indigo in the 16th century. In 1598 indigo was prohibited in France and parts of Germany, and dyers had to swear, often on the pain of death, that they would not use that dye. Nevertheless, in the 17th century indigo became one of the chief articles of trade of both the Dutch and the British East India Companies. Dauril Alden argues that, in fact, the indigo supplies in India were not sufficient to meet the European demand in the 17th century and that is why indigo cultivation was taken up in the New World as well.
In Japan, indigo became especially important in the Edo period (The Edo period (江戸時代 Edo-jidai), also called Tokugawa period, is a division of Japanese history running from 1603 to 1868) when it was forbidden to use silk, so the Japanese began to import and plant cotton. It was difficult to dye the cotton fiber except with indigo. Many years later the use of indigo is very much appreciated as a color for the summer Kimono Yukata, as the blue sea and the nature are recalled on this traditional clothing.
An indigenous variety of indigo began to be cultivated by Spanish overseers on the plantations of Honduras and the Pacific slopes of Central America in the 1560s. The indigo plant was known to early Guatemalan colonialists by the Nahuatl word xiquilite, and the dye was known to contemporaries as “Guatemalan Indigo.” M. De Beauvais Raseau, writing about indigo cultivation in the Eighteenth Century, stated that the Native Americans also knew about extracting dye from the plant. They called it “Tlauhoylimihuitl” and used it to darken their hair. It seems that indigo production continued to increase throughout the 17th century in the New World. The French colony of Saint Domingo eventually became the major producer of indigo, and this dye was also of the best quality. The English gained their first indigo-producing colony in this part of the world in 1655 when they captured Jamaica. However, it is unclear how important New World indigo was in the worldwide indigo market, as prices fluctuated and so did production numbers. By 1740 sugar had replaced indigo as the main crop of Jamaica, but, on the other hand, this was also the beginning of the indigo boom in South Carolina.

It seems that “Guatemalan indigo” did not enjoy as high a reputation in Europe as indigo from Asian countries. In 1746, when “A Friend to Carolina” wrote his tract encouraging the cultivation of indigo in South Carolina he emphasized the necessity of establishing a superior product: “All Kinds [of indigo dyes] are better or worse, as they are neat or pure; for those who make it in America, often maliciously mix it with Sand and Dirt, but the Cheat is easily discovered; as Indigo that is fine and pure will burn like Wax, and, when burnt, the Earth or Sand will remain.” He pointed out that in the Americas indigo dye was often made with the stems and branches of the plant instead of just with the leaves. He felt that this too might be detrimental to its quality — “But one ought to have the Leisure and Patience of the Indians, to undertake such a Work [stripping the leaves], and have Workmen as cheap as they are in that Country.”
Beauvais-Raseau, L’Art de l’Indigotier. Paris: L.F. Delatour, 1770.