Woad (Isatis tinctoria)
BRASSICACEAE, Mustard Family
Indigo (Indigofera tinctoria)
FABACEAE, Legume Family
Among the tales told about vegetable dyes, those spun about the Old World blue dyes, woad and indigo, are the most intriguing. Woad (Isatis tinctoria) was a native of southeastern Europe, presumably either around Greece and Italy or southwestern Russia, and spread quickly throughout Europe in prehistoric times. This plant became the dominant blue dye in Europe, especially in western Europe. Indigo (Indigofera tinctoria), on the other hand, was a native of southern Asia and provided the blue fabric pigments for Asia. In North America, certain Indian tribes, and most notably the Navajo, used blue legume dyes from species closely related to indigo.
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).
Nowadays spinners and weavers can make their own woad, if they are patient. One uses the young leaves; in fact, the old leaves turn blue, but this stage is too late to harvest the chemical for dyeing. For dyeing, fresh leaves are put into a jar and covered with almost boiling water. The jar is covered to exclude all air. In a while the liquid becomes colored and produces small bubbles. Alkali is added to the colored liquid, and then the solution is shaken until it becomes greenish. Woad is a tricky dye to get correct, and many do not have success even following the detailed recipes that exist. Some type of green liquid is the form of the solution for dyeing. The fabric is dyed greenish-yellow but turns blue when exposed to the air (air oxidation) and becomes relatively fast when put in an acid and then a soapy rinse.
Indigo (Indigofera means "indigo-bearing") is a subtropical shrub 1 to 2 meters tall that possesses the woad pigment in the leaves. Leaves are crushed and then soaked in water for fermentation (removal of the sugar). As in woad dyeing, the solution used in indigo dyeing is yellowish-green.
Woad was the dye that was used for many centuries in the British Isles; in fact, early inhabitants used it as a blue body dye to frighten opponents, and the Roman soldiers referred to these people as Picts, which is Celtic for "painted." Since Roman times, woad became extensively cultivated in northwestern Europe and was a major industry and trade item. In England the color Saxon green for Robin Hood and his men was obtained by first dyeing in woad and then in a yellow plant dye called wild mignonette (Reseda luteola, Family Resedaceae). Trade in woad was so important in western Europe that production was controlled by the mid-1200s.
Indigo held the same important status in Asia, where indigo plants were being used 5000 years ago. Production and trade of indigo was controlled by India. It is not surprising, therefore, that trouble would "ferment" when merchants tried to introduce indigo to Europe. Numerous fears and anxieties were given to woad growers about indigo by the woad merchants, who called it "devil food" and a bad drug, but who actually feared the indigo competition. A union was formed, called the Woadites, which was an international political group of woad producers, united to fight indigo. Laws were passed in England, France, and Germany to prohibit the importation of indigo. In the 16th century, indigo was brought to Europe by Dutch, Portuguese, and English traders from India. Slowly but gradually, indigo replaced woad as the preferred dye in western Europe, even though the pigment used in both was the same. Obstacles to indigo trade were dropped by the British when they occupied India and began the exploitative activities of the East India Company.
In 1649 Europeans also attempted to break the Indian monopoly on indigo by planting this species in the New World. The first crop of indigo in the New World was produced by Eliza Lucas Pinckney in South Carolina (1740s), but there indigo was passed over in favor of rice (Oryza) cultivation during the Revolutionary War.
World consumption of indigo in the 1800s was very large indeed, so in 1866 a German chemist named Adolph von Baeyer began his studies of the pigment and eventually elucidated its chemical structure so that it could be synthesized commercially. At the end of the 19th century, Germany was able to produce synthetic indigotine cheaper than the natural dyestuff, and thus Germany then took charge of supplying indigo. Some competition developed when an indigo factory was built at Ellesmere Port in England (1916). Hence, with supplies from India, the Far East, and Africa, as well as synthetic indigo and other blue substitutes, the blue plant dye industry lost steam and has been on the decline ever since.
Indigo is not a preferred fabric pigment in modern societies--it does bleed and fade with age, although the faded look is now one of its pleasing qualities. Indigo is a dye that can color cotton from a cold dyebath and still give fairly good color fastness. There are no synthetic dyes that have the identical color and physical characteristics of indigo and indigotine.