Woad
Isatis tinctoria
The blue that Caesar saw. The colour of a people who knew what they were defending.
Overview
Woad is a yellow-flowered member of the cabbage family that, through a sequence of fermentation, oxidation, and processing that is not intuitive from looking at the plant, yields a rich blue dye. It was the principal blue dye of northern and western Europe for at least three thousand years, until the trade routes that brought true indigo (*Indigofera tinctoria*) from India expanded in the sixteenth and seventeenth centuries. Julius Caesar described the Britons painting themselves with it before battle — *vitro inficiunt* — and the image of blue-daubed warriors has persisted in the popular imagination as the defining characteristic of a people who had, as things turned out, more than aesthetics to contend with.
Botanical Notes
A biennial or short-lived perennial, 60–120cm, with a rosette of grey-green, slightly hairy leaves in the first year and an erect, branching stem bearing numerous small, four-petalled yellow flowers in flat-topped corymbs from May to July in the second. Fruit a distinctive pendant, tongue-shaped silicle, 1–2cm, dark purple-brown when ripe, hanging in chains. Native to the steppes of central Asia and the Black Sea region; naturalised across much of Europe and established as a crop plant in Britain, France, Germany, and Scandinavia. The blue pigment is produced from the glycoside isatan B in the leaves, which converts to indoxyl and then indigotin (indigo) during fermentation processing. The processed dye yields the same indigo compound as tropical indigo but at lower concentration per unit of plant material.
Lore & History
The woad industry was one of the most economically significant agricultural activities in medieval England; the towns of Glastonbury, Coventry, and Lincoln were known for woad production and processing, and the Hanseatic trade in dyed wool relied heavily on English woad. The smell of the fermentation process — which required urine as a reducing agent — was notorious; in the seventeenth century, woad processing was banned near royal residences. When indigo imports made woad commercially unviable, the English woad growers petitioned parliament to prohibit the foreign dye and succeeded, briefly, in the late sixteenth century: an act of 1581 banned the import of indigo, calling it a "false and deceitful" drug. It did not hold. The Picts — the painted people, from the Latin *picti* — remain the most famous users of woad body paint, though whether they painted themselves with woad or with weld or with something else entirely is a question that has been disputed by archaeologists for decades.
Warnings
Safe. The leaves are edible — they were eaten as a bitter vegetable in pre-Roman Britain — and the plant presents no significant toxicity at any stage of processing or use. The dye itself is essentially pure indigotin, which is non-toxic. Contains glucosinolates as all brassicas do; these are mildly goitrogenic in very large amounts but not a practical concern. No contraindications for handling or use.