Indigo cultivation

Alizarin or l 2-dihydroxyanthraquinone is one of the most important dyes. Like indigo, the dye occurs in the plant (the madder root) as the glucoside of the leuco-compound. The cultivation of the madder plant, which, chiefly in southern France, extended over large areas, was brought to an end by the synthesis of the dye from the anthracene of coal-tar (Graebe and Liebennann, 1869). By distillation with zinc dust according to the method of Baeyer, these two chemists had previously obtained anthracene from alizarin. 

In the period 1700 to 1900, the production of what came to be known as natural indigo was carried out on a very large scale. The indigo plant was cultivated in enormous plantations, chiefly in India and the countries of South-East Asia and America. As much as one square kilometer was needed to obtain a tonne of indigo a year [2], The reason for such a high land requirement was simply that the plant material contains barely 1 % of the dye s precursor indican, the rest being biomass. 

Blue dyeings were also produced in Europe. Here the process involved using the woad plant (Isatis tinctoria) without isolation of the dye. The cities of Erfurt and Toulouse were important centres of cultivation [3], In the 1600s, Indian indigo captured the market in Europe because of its lower price and more brilliant shade. 

The increase in the production of the synthetic indigo has decreased the cultivation of the indigo plant, especially in India where the land formerly used for this purpose is now used for other crops such as rubber, turmeric, hemp, cotton, etc. 

South America. Indigos are still cultivated widely for their dark-blue dye, although similar chemicals have been synthesized and are now widely available. 

FIGURE 15. Gathering the indigo crop, India, around 1900. Aniline was first obtained from indigo, prior to isolation of the aromatic amine from coal tar and synthesis from benzene. Cultivation of the natural product declined following the introduction of synthetic indigo by BASF and Hoechst in 1897. Edelstein Collection... 

When the trade route to the East was opened up, in spite of much protest from the woad growers oriental indigo soon replaced indigotin from all other sources. Woad was then only cultivated for its value as an ingredient to... 

The indigo plant cultivated in India is sown, as seed, in February and, by August, has grown to a height of about 3 feet, at which stage the yield of the dye has reached its maximum of about 0-4 per cent of the weight of the plant, and the crop is harvested. The sap extracted from the plants is... 

In the 18th century, the spread of woad cultivation contracted, since British-Indian companies had established large Indigofera plantations, particularly in Eastern India. The yield of the colourant from Indigofera was around 30 times higher. From 100 kg of leaves one could obtain 2 kg of indigo. [9] So in 1897,... 

The advent of cheap synthetic alizarin resulted in the cessation of the cultivation of the madder plant. Some years later, most indigo plantations also became redundant. Natural indigo is a mixture obtained by fermentation and oxidation of the plant extract, and the principal coloured component is indigotin. Synthetic indigotin was available from the 1890s. 

Large-scale use of major natural dyestuffs was made possible by widespread cultivation of the pertinent plant species such as the madder and indigo plants for the dyestuffs themselves, and cactus plants as hosts for the scale insect, Dacty-lopius coccus, that fed upon them. As the appetite for these natural products grew, European entrepreneurs attempted to either improve upon the natural material (e.g., Drebbel s scarlet and Turkey red), or to synthesize dyes in the laboratory. 

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