Indigo is dying by hand. Indigo – the primary use for indigo is as a dye for cotton yarn, which is mainly for the production of denim cloth for blue jeans. On average, a pair of blue jean trousers requires 3 – 12 g of indigo. Small amounts for dyeing wool and silk.
Indigo dying industrial. Synthetic indigo is a substance created from benzene derivatives from petroleum, a fossil fuel that most of us realise is not in limitless supply. The benzene has to be treated chemicals, including hydrogen cyanide, to make it into indigo dye.