"In India, the natural indigo of commerce was extracted from the leaves of species of plants belonging to genus Indigofera. In India about 40 species of Indigofera genus are found, out of which four were commercially exploited for bulk production due to their higher dye content and their suitability to the climates and soil of the place of cultivation. These were Indigoferaarrecta, Indigoferasuffruticosa (I. anil), IndigoferaSumatrana and Indigoferatinctorial (Tolat, 1980, p. 50). From the leaves of these plants, the indigo dye was extracted by steeping the plants in water, beating the liquid obtained after steeping, collecting the settled dye from the vat, and then draining it to make the paste, boiling the paste and compressing it into the cakes and finally drying them to sell in the markets. These indigo dye cakes, which are very light in weight, were transported to various centres in India as well were exported. They also have no expiry date as they last for years. For example, the natural indigo cakes bought by author in 1979, still gives excellent colour and have not got spoilt. This could be one reason for feasibility of its export through the land and sea routes, which took years to complete the voyage, in the ancient times. " Link - //bit.ly/3kflPLc