Woad (Isatis tinctoria) is a plant yielding a blue pigment used in dyes, paint and medicine. A member of the mustard family, it's also called Asp of Jerusalem. Flowers are bright yellow. The leaves of the plant produce the blue dye.
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Both the plant and blue pigment are called woad. It's native to the Caucasus, central and western Asia and the steppe, and has been naturalized throughout Europe and North America.
Known at least since Neolithic times, woad is found in a cave burial in France, along with a vessel of kermes red. Woad seeds have been found in the cave of l'Audoste, Bouches-du-Rhône, France.
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Impressions of seeds of Färberwaid (Isatis tinctoria L.) or German indigo have been found on pottery in the Iron Age settlement of Heuneburg, Germany. The Hallstatt burials of the Hochdorf Chieftain's Grave and Hohmichele contain textiles dyed with woad.
One of the early dyes discovered by the ancient Egyptians is presumed to be "blue woad (Isatis tinctoria)." Expert Rosiland Hall states the ancient Egyptians create their blue dye "by using indigotin, otherwise known as woad."
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Celtic blue is a shade is known as glas celtig in Welsh, or gorm ceilteach in Irish language and Scottish Gaelic. Julius Caesar reports the Britanni color their bodies blue with vitrum, a word that means primarily 'glass', but also the domestic name for the woad.
Woad is an important dye in much of Europe during the medieval period. It's one of the three prominent pigments of the European dyeing industry, along with weld (yellow) and madder (red).
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In York, UK, a Viking Age dye shop with remains of both woad and madder have been excavated, dating to the 10th century CE. In medieval times, centers of woad cultivation arise in England, Germany, Italy, Normandy, Brittany and Languedoc in France.
The French area of the Lauragaisis becomes the biggest producer of woad (pastel). One writer comments "woad […] hath made that country the happiest and richest in Europe.
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To extract woad, a maker gathers leaves from the bottom of the plants. She shreds and steeps them in water at 80°C (176°F) for 10 min. It must cool quickly; one way is by placing the pot in a bin of ice. Dye is extracted by squeezing the leaves, which are then discarded.
Soda ash is dissolved in hot water. It's added when the woad mixture cools to 50°C (122°F) and aerated by whisking about 10 min. The solution is dark green. Woad pigment settles to the bottom. The liquid is removed and the pigment allowed to dry.
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The dye chemical extracted from woad is indigo, the same dye extracted from "true indigo", Indigofera tinctoria, but in a lower concentration. After 1498 CE, traders import an abundance of indigo from Asia.
Some regions pass laws to protect the woad industry from competition by indigo trade. Rumors claim imported indigo causes yarn rot. In France, Henry IV, in an edict of 1609, forbids on pain of death use of "the false and pernicious Indian drug".
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The woad plant's roots are used in traditional Chinese medicine to make banlangen (bǎnlán'gēn 板蓝根), an antiviral treatment. Banlangen is taken as herbal medicinal tea in China for colds, throat and tonsil ailments. As tea, it's brownish and mildly sweet.
With synthesis of both woad and indigo pigment in the 20th century, the woad dye industries collapse. People with modern experience using woad as tattoo pigment claim it doesn't work well. The ink pigment is caustic when injected and scars the skin.
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Woad is biodegradable and safe in the environment. In Germany, it's tested for use protecting wood from decay without dangerous chemicals. In the UK, use of woad is increasing in inks and dyes. Textile artists also work with natural woad.
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