“There are many plants that contain indigo and there are many terms for indico - indigotin, indican, anil, nila, xiquilite, gara, landian and ai - but all the plants contain (and all the terms refer to) the same dye.”1

“...The queen of all dyes (indigo) is still more mysterious since the dye matter itself - indican in the indigo plants and isatan B in woad - is actually invisible.”1

There are many ways to retrieve the indigo from a plant. Some methods are bathing, steeping, drying, composting, and mounting an indigo dye vat.1

“In Japan, dark blue is known as kon and indigo blue as ai (like the plant). Nando and asagi are intermediate shades of blue and kamenozoki is the term for several shades of pale blue.”1

“Indigo dying is a universal practice. The process unfolds in the same manner the world over, involving exactly the same the same steps: cultivation or wild harvesting of the plant, extraction of the pigment, preparation of the dye bath, and dyeing of the cloth or yarn.”1

“There are hundreds of varieties of blue-dye plants. Some trail and others climb and cling on to supports. Some are sown and carefully tended, while the wild varieties are gathered in the forest or in the bush. Woad is adapted to a temperate climate, whereas Indigofera plants are happiest in the heat of the tropics.”

Source: 1.) INDIGO, The Color That Changed The World by Catherine Legrand. Published by Thames & Hudson