Indigofera tinctoria 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 16^th 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 17^th 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 17^th 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.
 

Raseau, who was captain of the militia on Saint Domingo prior to 1770, discusses the history of indigo in all the regions of the world where it could be grown. He gives various methods that were employed for extracting the dye and then goes into greater detail on indigo production in South and Central America. His wonderful little book contains diagrams of the plants, the process of making indigo dye, as well as the ideal plantation. Indigo plantations did not require much labor except during July, August and September when the plants were cut, fermented and the dye was extracted. Because it was thought that the Indians were particularly susceptible to the diseases that bred around the fermentation vats, plantation owners claimed that they did most of the field work, while Black slaves extracted the dye. In reality, the division of labor was probably not so strict — particularly since Black slaves were in relatively short supply and were often more expensive to hire than the Indians.


John Stedman in his "Narrative of five years" expedition described the extraction of the dye throughly. Stedman was invited to view the process of making indigo dye at the plantation of the governor of Surinam and he gives the following account of it:

"When all of the verdure is cut off, the whole crop is tied in bunches, and put into a very large tub with water, covered over with very heavy logs of wood by way of pressers: thus kept, it begins to ferment; in less than 18 hours the water seems to boil, and becomes of a violet or garter blue colour, extracting all the grain or colouring matter from the plant; in this situation the liquor is drawn off into another tub, which is something less, when the remaining trash is carefully picked up and thrown away; and the very noxious smell of this refuse it is that occasions the peculiar unhealthiness which is always incident to this business. Being now in the second tub, the mash is agitated by paddles adapted for the purpose, till by a skillful maceration all the grain separates from the water, the first sinking like mud to the bottom, while the latter appears clear and transparent on the surface: this water, being carefully removed till near the coloured mass, the remaining liquor is drawn off into a third tub, to let what indigo it may contain also settle in the bottom; after which, the last drops of water here being also removed, the sediment or indigo is put into proper vessels to dry, where being divested of its last remaining moisture, and formed into small, round, and oblong square pieces, it is become a beautiful dark blue, and fit for exportation. The best indigo ought to be light, hard, and sparkling."

These blocks of indigo were what was so highly prized on the European market.

Demand for indigo dramatically increased during the industrial revolution, in part due to the popularity of Levi Strauss's blue denim jeans. The natural extraction process was expensive and could not produce the mass quantities required for the burgeoning garment industry. In 1865 the German chemist Johann Friedrich Wilhelm Adolf von Baeyer began working with indigo. His work culminated in the first synthesis of indigo in 1880 from o-nitrobenzaldehyde and acetone upon addition of dilute sodium hydroxide, barium hydroxide, or ammonia and the announcement of its chemical structure three years later. BASF developed a commercially feasible manufacturing process that was in use by 1897. In 1905 Baeyer was awarded the Nobel Prize for his discovery.

Recipe of dyeing wool with indigo

Indigo with Urine The proportion needed is double the weight in grammes of powdered indigo to litres of urine. Indigo is stirred little by little into urine fermented for ten to fourteen days outside at a temperature of at least 24°C (75°F) in a sealed container. After another ten to fourteen days outside in the sun, with daily stirring, the indigo should have dissolved and the liquid can be used for dyeing. One generous quarter litre of the liquid added to 25 litres (5 ½ gallons) of water will dye one kilo of wool.