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Isatis tinctoria, page 2 of 2

Common Names: Woad

Dye Extraction: Historically, indigo has been obtained from the leaves of Isatis tinctoria by a complex process that involved fermentation. The dye is rarely used nowadays, having been replaced at first by pigment from the tropical plant Indigofera tinctoria and more recently by synthetic dyes, which have reduced the use of both of these plants. Traditionally, the young leaves of the plant were harvested by hand throughout the summer. A large workforce, including women and children, was employed from June to November in the woad fields. The harvested leaves were partially dried in the sun and then crushed in a mill. The resulting paste was then hand kneaded into cakes called woad balls. The kneading process gave the workers blackened hands.

Woad balls were dried and stored until needed. To prepare the dye, the woad balls were ground into powder and piled in deep layers in 'couching houses'. The layers were watered and allowed to ferment for two weeks. Fermentation of these woad balls produced a foul smell due to the release of sulphur compounds from the decaying leaves. Because of this, Queen Elizabeth I famously decreed that no woad processing would be allowed within five miles of her residences. After two weeks fermentation the mass was mixed up and formed back into cakes of 'couched woad' to go to the dyer. The couched woad is mixed with lime-water and warmed to make a dye vat.

Queen Elizabeth I of England

A process for dye extraction, described in 1846, forms the basis for the use of woad today by artists and craftspeople. Woad leaves are steeped in hot water, 80 - 90C, for up to 30 minutes, lime is added to the liquid and then the whole mixture is agitated to precipitate the indigo. The dye can be strained off through muslin.

Woad produces a very good quality dye that still finds some use amongst artists who want to work with natural dyes. A good quality green is obtained by mixing it with dyer's greenwood Genista tinctoria. Woad is also used as a base or mordent for black dyes.

Isatis indigotica

Common Names: Chinese Woad, Tein-cheing

Geographical Distribution: North China

Habitat: Unknown

Description: This plant is very closely related to European Woad, it is hardy Biennial/Perennial growing with a more upright habit. Believed to be richer in blue dye than Isatis tinctoria.

Notes on use: Isatis indigotica is cultivated as a dye plant in the north of China, where it is called Tein-cheing. The dye is obtained by a process closely related to that employed in the preparation of indigo from woad (as described above). Tein-cheing is used by Chinese dyers as a paste to dye cotton.

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