This is an ancient dye plant in the cabbage family (Brassicaceae). Blue dye extracted from its leaves has been used, mainly in Europe, for thousands of years. Seeds have been found in caves in France dating back to the Neolithic period. The extraction process involves heating the leaves in water, adding an alkali and then extracting the oxygen using a reducing agent. After the fabric has been submerged in the dye vat it turns blue upon exposure to the air. Green can be achieved by overdying with yellow from weld or buckthorn berries.
