One of the oldest natural dyes used by man, extracted from the stem and leaves of the indigo plant, indigofera tinctoria and indigofera anil, and from woad plants. Its intense blue hue has been popular from ancient times. It is a vat dye and thus time consuming to use. At one time indigo was exported in large quantities from India but with the advent of chemical dyes, the demand for natural indigo has reduced, though still considerable amounts are needed for the denim world.