Woad, a plant of the mustard family, isatis tinctoria, formerly cultivated for the blue dye yielded by its foliage. The genus isatis comprises 25 or 30 species, all of the old world. The woad has been so long in cultivation that its native country is uncertain; it is naturalized throughout Europe, as far north as Sweden, and is occasionally found in old gardens in this country. It is a biennial, from 2 to 4 ft. high, smooth and glaucous, or slightly hairy below; the obovate or oblong radical leaves are coarsely toothed and petioled, the upper sessile and arrow-shaped; the numerous branches are clothed with small yellow flowers, which are succeeded by hanging flat pods, each containing a single seed. The plant requires rich soil, and is sown in drills, after thorough preparation; the foliage is collected when the plant is in flower, the leaves being picked off when their tips turn yellow, and the picking is repeated several times. The leaves, being slightly dried, are ground to a pulp, which is formed into heaps under shelter, but well exposed to the air.
As with indigo, the coloring principle is developed by fermentation, which in woad takes place in the heaps, and requires about a fortnight for its completion; the mass, after thorough mixing, is made into cakes by hand or in moulds of one to three pounds each, and these in drying undergo a second partial fermentation, upon the proper management of which the value of the dye greatly depends; in this form it is called by the French pastel. Woad was known as a dye or pigment in very early times, and is mentioned by Pliny as glastum; it was in use by the ancient Britons to dye their bodies for seme religious ceremonies. Before the introduction of indigo the consumption of woad was large; the annual product of Upper Languedoc alone was 40,000,000 lbs. As indigo gives a better color, and one pound of it produces an effect equal to 50 lbs. of woad, it has almost entirely superseded the latter, though woad is still sparingly cultivated for domestic dyeing; its color, though not so fine, is regarded as more permanent than that from indigo.
Woad (Isatis tinctoria).