DR JEREMY BURGESS / SCIENCE PHOTO LIBRARY DR JEREMY BURGESS / SCIENCE PHOTO LIBRARY
Part of a mature seed-bearing raceme of Chinese Woad, Isatis indigotica, a member of the Cruciferae ( cabbage ) family. Woad ( in Europe, I. tinctoria ) has been a source of blue dye for thousands of years. Traditionally, the dye was made by soaking chopped up plant material to soften the tissue, then fermenting the mass in vats, followed by treatment with urine. This produces the soluble form of the dye - âwhite indigoâ. Cotton, wool and silk treated with white indigo in solution turn blue on exposure to air. The most familiar use of indigo today is to dye denim for jeans. Due to the polluting nature of chemical synthesis of indigo, the use of Isatis spp.
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