There are many varieties worldwide of Indigo based blue dyes. In Europe the earliest evidence of woad (Isatis tinctoria) dyed textiles was found in the Halstatt salt mines (1500 BCE). The woad plant has be found in Mediterranean areas, temperate Europe and southwest Asia. Other natural plant dyes from prehistory include madder and weld.

The blue colour is extracted from the woad leaf. A traditional fermentation method exploits aerobic bacteria to remove oxygen, thus allowing anaerobic bacteria to convert the insoluble indigo present in the leaf into a soluble form known as indigo white (leucoindigo). It is also necessary to have a source of alkali to enable the indigo white to dissolve. When the yarn or cloth is submerged in the vat and then carefully removed, on exposure to air it will oxidise and change colour from a pale yellow/green to blue, which will deepen through repeated dips…never predictable, always magical.