History of Technology in India, Vol. I: From Antiquity to c. 1200 A.D. v1.c20.s1.5

v1.c20.s1.5

Since all dyes are not soluble in water, they have to be rendered water soluble by reduction or they have to be synthesised on the fibres (usually cotton) by means of methods like diazotization. Indigo or nīlī which have been very popular ever since the pre-Christian era and was an article of export to Egypt and other countries, is also an insoluble dye (vat dye) and our ancients knew the technique of making it soluble by reduction with which the dye could be impregnated in the cotton fibres by exposing to air or by oxidization. Besides alum, iron sulphate, etc., rind of lemon, flower of cotton, lime, lemon, green dried mangoes, myrobalans etc. were also used as fixing agents or mordants. Mordanting effect of each varied and each one influenced that final colour obtained. In some dyes, alum produced yellow colour, in other it yielded orange blue (Jaggi, I.p. 165)