Woad (or glastum) is the common name of the flowering plant Isatis tinctoria in the family Brassicaceae. It is commonly called dyer's woad, and sometimes incorrectly listed as Isatis indigotica (a newer and invalid name for the same plant). It is occasionally known as Asp of Jerusalem. Woad is also the name of a blue dye produced from the plant. Woad is , to rhyme with road.
Woad is native to the steppe and desert zones of the Caucasus, Central Asia to eastern Siberia and Western Asia (Hegi), but is now found in southeastern and some parts of Central Europe as well. It has been cultivated throughout Europe, especially in Western and southern Europe, since ancient times.
The first archaeological finds of woad seeds date to the Neolithic and have been found in the French cave of l'Audoste, Bouches du Rhone (France). In the Iron Age settlement of the Heuneburg, Germany, impressions of the seeds have been found on pottery. The Hallstatt burials of Hochdorf and Hohmichele contained textiles dyed with woad.
Julius Caesar tells us (in de Bello Gallico) that the Britanni used to mark their bodies with vitrum; this has often been assumed to mean that they painted or tattooed themselves with woad. However vitrum does not translate to "woad", but probably more likely refers to a type of blue-green glass which was common at the time. The Picts may have gotten their name (Latin Picti which means painted folk or possibly tattooed folk) from their practice of going into battle naked except for body paint or tattoos. (This has been commemorated in the humorous (modern) British song The Woad Ode.) However, more recent research has cast serious doubt on the assumption that woad was the material the Picts used for body decoration. Contemporary experiments with woad have proven that it does not work well at all as either a body paint or tattoo pigment. Highly astringent, when used for tattooing or placed in wounds woad produces quite a bit of scar tissue and, once healed, no blue is left behind. The common use of dung as an ingredient in traditional woad dye preparations also make it unlikely to have been suitable for application to wounds.
In Viking age levels at York, a dye shop with remains of both woad and madder dating from the tenth century have been excavated. In Medieval times, centres of woad–cultivation lay in Lincolnshire and Somerset in England, Gascogne, Normandy, the Somme Basin (from Amiens to Saint-Quentin), Toulouse and Britanny in France, Jülich, the Erfurt area in Thuringia in Germany and Piedmont and Tuscany in Italy. The citizens of the five Thuringian woad-towns of Erfurt, Gotha, Tennstedt, Arnstadt and Langensalza had their own charters. In Erfurt, the woad-traders gave the funds to found the University of Erfurt. Traditional fabric is still printed with woad in Thuringia, Saxony and Lusatia today: it is known as Blaudruck (literally, 'blue print(ing)').
Medieval uses of the dye were not limited to textiles. For example, the illustrator of the Lindisfarne Gospels used a woad-based pigment for blue paint.
The blue pigment in woad is the same as in indigo dye, but it is less concentrated. With the European discovery of the seaway to India, great amounts of indigo were imported. Laws were passed in some parts of Europe to protect the woad industry from the competition of the indigo trade. Indigo was proclaimed to rot the yarns as well. "In 1577 the German government officially prohibited the use of indigo, denouncing it as that pernicious, deceitful and corrosive substance, the Devil's dye." "... a recess of the Diet held in 1577 prohibited the use of 'the newly-invented, deceitful, eating and corrosive dye called the devil's dye.' This prohibition was repeated in 1594 and again in 1603. With the development of a chemical process to synthesize the pigment, both the woad and natural indigo industries collapsed in the first years of the twentieth century. The last commercial harvest of woad until recent times occurred in 1932, in Lincolnshire, Britain.
In Germany, there are attempts to use woad to protect wood against decay without dangerous chemicals. Production is also increasing again in the UK for use in inks, particularly for inkjet printers, and dyes, as woad is biodegradable and safe in the environment, unlike many synthetic inks. Isatis tinctoria is viewed as an invasive species in parts of the United States.
Indigowoad Root (Chinese: 板藍根; pinyin: bǎn lán gēn) is a traditional Chinese medicine herb that comes from the roots of woad, but often incorrectly listed under the synonymic name, Isatis indigotica. It is also known as Radix Isatidis. The herb is cultivated in various regions of northern China, namely Hebei, Beijing, Heilongjiang, Henan, Jiangsu, and Gansu. The roots are harvested during the autumn and dried. The dried root is then processed into granules, which are most commonly consumed dissolved in hot water or tea. The product is very popular throughout China, and used to remove toxic heat, soothe sore throat and to treat influenza, measles, mumps, syphilis, or scarlet fever. It is also used for pharyngitis, laryngitis, erysipelas, and carbuncle, and to prevent hepatitis A, epidemic meningitis, cancer and inflammation. Possible minor side effects include allergic reactions and dizziness; only large dosages or long term usage can be toxic to the kidneys. These treatments have not generally been evaluated clinically.