A natural blue dye
can be produced from the woad plant
). Until the 17th century woad and indigo
were the only blue dyes available in Europe
The Picts got their name (Latin Picti which means painted folk or possibly tattooed folk) from their practice of going into battle naked except for decorations made with woad war paint.
Formerly cultivated, Isatis tinctoria is now viewed as a noxious weed in many placed in the United States.