Leaves of these plants contain upto 0.5% of Indican which when exposed to oxygen produces the blue substance Indigotin. Cakes of this were a major item of trade from India. Crossing the sea to the Middle East, Arab merchants would carry it across deserts to the Mediterranean and into Europe where it was a highly prized item, used in the colouring of silk, in paintings and murals, and in cosmetics. (Read More)
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