Indigo is an extract prepared from cultivated plants of Indigofera Tinctoria. Indigo can give the clearest blues of all values from
pale sky blue to the deepest darkest navy.
There are many types of indigo vats - each can be used with natural or synthetic indigo. At the Maiwa Handprints studio we use either the zinc-lime vat or the lye-hydrosulfite vat. The zinc-lime vat can be maintained and kept going for several months or even up to a year. When disposing, however, it must be taken to a proper waste-disposal site because of the zinc content. The lye-hydrosulfite vat is ideally used within a day or two but due to its reaction process it can be dispossed of normally. The stock solution, however, can be kept for up to six months. See our instructions for the dyevat recipe.
Thiourea Dioxide Thiourea dioxide is a reducing agent and an excellent substitution for sodium hydrosulfite in color stripping and discharge. It is safer to use, has a greater strength, and does not lose its strength over time. It can be used for stripping cellulose fiber or bleaching wool or silk. It must be used in a well ventilated area or outside.
Natural Indigo use may go back as far as four-thousand years. With the possible exception of iron buff and tannins, indigo has probably seen longer continuous use than any other dye.
Natural indigo is obtained from indigo bearing plants. The most significant one being indigofera tinctoria. This green shrub grows wild and is also cultivated in India, China, Indonesia, and South America.
The plant material does not produce the finished dye, instead it gives a colourless glucose-based substance called indican. When fermented a bacterial enzyme is produced which consumes the glucose and leaves indigotin. At this stage the indigotin (what we know as indigo dye) is insoluble in water. It is at this point that the powder is extracted if it were to be stored or shipped for trading.
Indigo must be chemically reduced prior to dyeing. In its reduced form it is called indigo white and is soluble in water. When fiber is immersed in the indigo dyebath (which is amber to yellowish green) it will be penetrated by the soluble indigo white and a molecular combination accurs. When the fiber is removed from the vat and is exposed to air, the indigo white oxidizes back to the insoluble blue form where it remains in relative permanence.
Indigo was first synthesized in 1880 by Adolph von Bayer. Synthetic indigo is chemically identical to natural indigo and has almost completely replaced it. Synthetic indigo can be made more cheaply than natural indigo, it is more uniform in its concentration, and it dyes more evenly.
Yet there is a magical charm to natural indigo, not the least of which is its amazing history and the wealth of folklore and belief that goes with its use. Some believe that the naturally occuring impurities give natural its own personality and create subtle variations in tone. Natual indigo is much sought after by textile artists.
