Indigofera tinctoria L. is a perennial of the pea family that can grow to seven feet. The leaves are pinnate: nine to thirteen small leaflets grow from a common leaf stem. The insignificant white-red flowers grow in stocky clusters. This indigo plant is probably native to India , but because it can be easily cultivated, it has become widely distributed; under the Arabs and it went as far as Moorish Spain. Shortly before the plants blossom, in the early morning - often before sunrise - they are cut above ground. The branches are bundled and placed whole in masonry containers. After perhaps three-foot-high layer of vegetation has been trodden down and weighted with segments of tree trunks, it is covered with water. At temperatures greater than 30°C ( 86°F ), a fermentation process begins.The enzymes in the plants and the omnipresent bacteria break down the indican in the leaves into soluble yellow indoxyl and glucose. Carbon dioxide is released in this process and bubbles off. The entire fermentation process continues for at least 12 hours. When the resulting indoxyl comes in contact with oxygen on the surface, an iridescent layer of indigo forms. When the fermentation has concluded, the liquid with the yellow indoxyl is drained off into a lower-lying basin. In smaller dye operations, it is left in the basin and the plant material is removed. Now the hours-long oxidation process starts. The yellow liquid is stirred up strongly, either with feet and legs or with simple machinery, so that as much oxygen as possible comes in contact with the indoxyl and via oxidation forms insoluble indigo.
Historical Data
The use of Indigofera tinctoria L. in India dates back to the Indus Valley period between the 4th and the 2nd millennium BC. Indigofera tinctoria is native to India one of the oldest known centres of indigo dye production. The association of India with indigo is revealed in the Greek word for the dye, indikon, meaning 'blue dye from India or more literally Indian substance. The Romans used the term indicum, which passed eventually into English as the word indigo. Many species of the Indigofera genus give blue indigo dye, of these Indigofera tinctoria is believed to give the highest yield (under ideal growing conditions). The name indigo also shows that trade in Indian indigo was already well established during the Greco-Roman period, and by implication that cultivation and processing of indigo were also well established.The Romans used indigo as a pigment for painting, for medicinal and cosmetic purposes. It was a luxury, however, being imported from India to the Mediterranean by Arab merchants. The historical record of indigo is patchy, but references were made by Marco Polo who saw indigo at present day Quilon in the state of Kerala in 1298. In 1498 the Portuguese explorer Vasco da Gama discovered a sea route to India . This enabled direct trade with India and the Far East . Until this time trade was conducted over land, the routes were long and dangerous. In Alexandria and Baghdad important cities along the trade routes, Greek and Persian merchants levied heavy taxes on luxury goods like indigo. Opening the sea route bypassed these tax sites and directly resulted in a significant rise in the amount of tropical indigo imported into Europe .Asian indigo arrived through ports in Portugal , the Netherlands , and England . Not all of Europe was thrilled with the newly abundant supply of tropical indigo. In England the use of imported indigo was prohibited by law from 1558 to 1685. While in France and Germany importation of indigo was outlawed in 1598, these prohibitions reflect the wealth and power of the woad ( Isatis tinctoria ) dye industry, an industry that eventually failed due to the import of tropical indigo. Because indigo was so valuable, many European powers established indigo plantations in their tropical colonies. Indigofera tinctora plant was imported from India to other tropical or sub-tropical destinations. British interests saw indigo become a major crop in Jamaica and South Carolina .France owned the indigo plantations of Saint Domingo and Spain imported indigo dye from its colonies in South America , were they established plantations using an indigenous Indigofera species. D2.2.2_fichiers/image052.jpg Photo: R. Karadag The East India Company imported massive volumes of Indian indigo in the mid 1600s. Its use in Europe was clearly a threat to native woad ( Isatis tinctoria ) growers. Protests led to the ban of indigo in Britain and other European countries. Despite this, European woad plantations and factories rapidly disappeared. The cultivation of indigo on a large scale started in the 16th century in India and this was documented by European visitors in the 16th and 17th centuries, particularly in the north of India .The British established commercial cultivation and production of indigo. Initial plantations began in 1777, and by 1788 most of the production of indigo purchased by the East India Company originated from Bengal . The system became deeply exploitative from 1837 when 'planters' were accorded permission to own land. Vast quantities of indigo were concentrated around Bengal, particularly in the district of Champaran which is now in Bihar . This area was the focal point for processing and trade. As a dye it replaced American supplies which had been disrupted during the American Revolution. It was in great demand to supply the textile industries of the Industrial Revolution and was used to dye European military uniforms. The chemical process of indigo dyeing was only unravelled in the 1870s, opening the way for chemical substitutes.This was catastrophic to the Indian indigo economy and it had a profound effect on the movement for independence in India . By 1914 only 4% of the total world production came from plants. The total production of natural indigo today cannot be calculated, probably tons. The largest portion is used by local Indian and Pakistani weavers. Natural indigo is, however, exported in small but increasing amounts from India , Mexico , El Salvador . And Pakistan to Europe and America , where it is used mainly by hobby dyers. Indigofera tinctoria L. is only one of over 800 members of the Indigofera family - 600 alone in Africa - which is indigenous worldwide in tropical and subtropical regions. The botanical classification of this large group continues to be a problem for botanists. The last revision of the classifications was in 1984. Besides Indigofera tinctoria, about a dozen, more of the 800 subspecies are used as a source of indigo and are also cultivated.