Illustration of German woad mill in Thuringia from an 18th century book by Daniel Gottfried Schreber .

Last week I blogged about the history of the color purple. In past posts I’ve talked about the color red, and the color green. Today it’s going to be the color blue.

Perhaps you’ve seen the movie Braveheart, which stars Mel Gibson as a thirteenth-century Scottish warrior named William Wallace. Wallace led a rebellion against the British, who eventually captured and rather enthusiastically executed him. In the movie’s battle scenes, Wallace and his men have smeared their skin with a lovely blue war paint–called woad. (There’s a link to a picture, here.) The effect is pretty striking, and warrior-like. But it is also anachronistic; Britons did paint themselves blue when they went into battle, but they were fighting the ancient Romans, not the British, and they did so in the first, not the thirteenth, century. Whatever. On to woad.

Producing woad was a nasty, smelly business. The plant, Isatis tinctoria, used to be found throughout Europe. The leaves were picked, then crushed and kneaded into balls, which turned the workers’ hands black. The balls were dried and then ground into powder. Then the powder had to be watered and allowed to ferment and oxidize. This process was called couching. When it was dry, the powdered woad was packed and sent to the dyer.

The dyer poured hot water onto the woad and mixed it with urine. Then the mixture was left to ferment for several more days. The fermentation process produced a horrible, sulfurous odor which smelled, frankly, like poop. It smelled so disgusting, Queen Elizabeth the 1st banned woad production within five miles of any royal residence. But it did turn fabrics a lovely shade of blue.

Woad was used in England to dye the coats of military officers and policemen as late as the 1930s.