"Dyer’s Woad, French Guède (supposed to be derived from Gaudum, now Gualdo, the name of a town in the Roman States, where it was extensively cultivated), was formerly much cultivated in Britain for the dye extracted from the leaves. It is now nearly superseded by indigo, but is still cultivated in the south of France and in Flanders, as its dye is said to improve the quality and colour of indigo, when mixed in certain proportions. Woad is cultivated to a small extent in Lincolnshire and Woad mills are still worked at Wisbech, but not for the dye itself, the produce fixes true indigo, and is also used to form a base, or mordant, for a black dye.
Woad belongs to a genus spread over Southern Europe and Western Asia, and from having been much cultivated in many parts of Asia and Europe, has become established in stony and waste places as far north as Sweden. It is found in many parts of Great Britain, but not fully naturalized, except near Tewkesbury, where, according to Hooker, it appears to be indigenous. At the earliest time in the history of Britain it must have been plentiful in the country, since Caesar found the natives stained with it, but afterwards, probably from its extensive use, it became less common, and we find our Saxon forefathers importing Woad to dye their home-spun cloth. Their name for it was Wad or Waad, whence the English name woad…."