Human beings have an insatiable appetite for colour, but the everyday gaudiness of our world is modern. We can dress as showily as birds (including crows - 70 to 90 per cent of clothes are dyed black) because we have found ways to stain pale yarns in strong colours. During the last 150 years the whole spectrum has come to be cheaply available, as it has become possible to synthesise dyes which previously had to be extracted from plants and animals.
Dyes are tricky. Unlike paint - pigment carried in suspension in a medium which sticks it to a surface - dyes must adhere to the substrate molecule by molecule. Some do it directly; other dye/fabric combinations need an intermediary - a mordant - in which to dissolve the dye to make it bite. Consider what used to have to be done in order to dye with indigo (the process has certain things in common with brewing). Leaves from one of the plant species which contain indican, the precursor of the dye, are steeped in a vat. Lime (or urine, or wood ash water - something to keep the contents alkaline) is added. Fermentation turns indican into indoxyl. Cloth can be dyed directly in the fermentation vat, in which case the indoxyl is oxidised to become indigo when the steeped cloth is exposed to the air, and the liquid which looks greenish yellow in the vat turns blue.
LRB 14 December 2000 | PDF Download