Woad is a temperate herbaceous biennial, which produces a basal rosette of leaves during the first year and a single stem that eventually bears yellow flowers the second year. The leaves on the erect stem are lance-shaped and have no petiole. In some parts of the world, this species is a noxious weed, and it is rarely cultivated any more, although woad can be grown easily in temperate gardens.

The dye of woad is no longer manufactured on a commercial basis, but there are accounts of the process. In olden times, the leaves were picked by hand, crushed with wooden rollers, and then hand-kneaded into 3-inch-diameter balls. This kneading gave the workers blackened hands. Afterwards, woad balls were dried on trays and stored until needed; eventually the balls were ground into a powder by rollers and piled into deep layers in special "couching houses." The layers were watered and allowed to ferment; there had to be a breakdown of indican, a sugar-bearing molecule, to the dyestuff indigotine (analogous to vanillin production). Fermentation of these leaves produced horribly foul odors, probably because woad has sulfur-containing chemicals in the leaves. (Queen Elizabeth I decreed that no woad processing would be allowed within five miles of her residences.) After two weeks of fermentation, the leaves were dried; this powder contained indigotine. Commercial production of woad ceased after the 1932 woad crop was processed in Lincolnshire, England (Skirlbeck Mill).

Source:http://www.botgard.ucla.edu/html/bot...tis/index.html