Dmitry Kostyukov for The New York Times Once the only blue dye in Europe, woad pigment made a fortune for the sun-rich Toulouse area during the Renaissance, when it also was called Toulouse’s ...

The root of the madder plant produced a red colour, woad offered blue and yellow was derived from weld. Plants were soaked in hot water and wool was immersed in the dye bath. Stale urine may have ...