Harvested plants must be treated carefully before extraction, and leaf staining is to be avoided since the plant leaves contain the enzyme needed to hydrolyze the relatively stable indican into the unstable indigo precursor indoxyl. Indigo, a dark blue colourant, differs from all natural dyes since it is produced when the extract of the plant, crushed or macerated in water, reacts on exposure to oxygen in the air, and it is insoluble in its blue form which it cannot impregnate and become fixed to textile fibers [45]. To get rid of any soil that might be stuck to the indigo plants before extraction, it can be good to give them a thorough rinse [45]. Primary washing safeguards against soil compounds reacting with indoxyl to produce nonindigotin oxidation products, reducing yield, and it additionally protects against fine soil particles being carried through the process and contaminating the final pigment product, lowering purity [45].