Woad, a plant which yields indigo dyestuff, was economically crucial in medieval Europe, supporting many livelihoods through its production. It was used not only for blue hues but also as under and top dye in the creation of various colors. France was a key region for woad cultivation, but woad trade extended across Europe. Due to its profitability, woad was tightly regulated with dyers and merchants holding significant market influence. However, during the colonial era, the European woad industry was threatened by a rise of imported indigo from Indigofera, which produces a higher concentration of indigo. This led to a smear campaign and even bans on imported indigo, sometimes under the penalty of death. By the 17th century, the superior yield and cost-effectiveness of Indigofera indigo led to its widespread adoption in Europe.
In Europe, woad was processed in urine dye vats. Urine is effective in reducing indigo, balancing alkalinity, and acting as a natural detergent and mordant. It is particularly compatible with wool. These vats, common in 18th century Europe, are still used by some dyers today.