Since synthetic indigo dye is being used ,use of natural indigo dye has almost became extinct , but in recent years, the demand for natural dyes has been increasing in many countries again, because of health and pollution effects and a revival of interest in the relationship between dyes and culture. In present time, indigo is still cultivated for dye on a small scale basis in India (particularly in the northern part of Karnataka) and in some parts of Africa and Central America. It is frequently grown as a secondary crop. Dissemination is usually by seeds which are sown at first in seed beds or directly into the field. Germination takes about 4 to 5 days. When the plants are about 4 to 5 months old and starts flowering then the branches are harvested. At 3 to 4 months intervals three times a year the plants could be continued to be harvested. The total life span of the plants could range from time period 2 to 3 years.
A. For Natural Indigo Dye
. The leaves of indigo go through a process of fermentation and then oxidized to yield the blue dye. Traditionally fermentation was carried out by bacteria. The harvested plants first of all, packed into tanks and is covered with water. After a few hours of soaking the plants in water, the leaves become saturated and fermentation begins. A thick layer of bubbles and foam forms at the top of the tank. The process can be so vigorous that planks are placed on top of the tub to keep the plants in. This process can take up to a day and a half to complete, but the timing has to be perfect .The indigo makers will smell and taste the fluid to check whether the dye is ready or not. Even if an hour is taken extra it could ruin it. As soon as the liquid tastes sweet and is a dark blue colour, it is drained off into another vessel at a lower level, leaving the plants behind. The liquid now formed contains indoxyl.
. To stimulate oxidation of the indoxyl the liquid is stirred continously for many hours for it requires oxygen for oxidation. On alternative basis people will get into the vats to tread up and down to stir it up. After sometime the liquid turns a yellow-brown colour with floating dark blue patches. The solution is left to rest and the insoluble indigo settles to the bottom of the tank as a bluish sludge. To remove impurities and to stop the enzyme reaction which made the indigo the water is drained and filtered. The sludge is then dried to produce indigo 'cake' which is cut into cubes or made into balls.
. The Japanese used another method of extracting indigo from the polygonum plant, the plant is mixed with wheat husk powder, limestone powder, lye ash, and sake in this method of extracting indigo. The mixture is allowed to ferment for about one week to form A dye pigment which is called sukumo is formed from the fermented mixture.
. The indigo was used to be dissolved in stale urine in Europe as a pre-industrial process for dyeing in earlier times .The water-insoluble indigo is converted to soluble substance known as indigo white or leucoindigo by urine, which produces a yellow-green solution. After the indigo white oxidizes the fabric turns into blue color fabric.
. Another preindustrial method, used in Japan, was to dissolve the indigo in a heated tub in which a culture of thermophilic, anaerobic bacteria was maintained .Insoluble indigo could be converted into soluble indigo white by certain specific species of bacteria when they generate hydrogen as a metabolic product. Cloth dyed in such a vat was decorated with the techniques of shibori (tie-dye), kasuri, katazome, and tsutsugaki.