Sanjan, a port in Gujarat that exported indigo, was a key junction in early medieval trade networks. The documents even used the Sanskrit word for indigo, nili, as a suffix for the names of some Arab merchants who traded the dye. The genizah documents - a set of over four hundred thousand papers found in Fustat, Egypt, containing commercial and administrative records from the ninth to nineteenth centuries - suggest a thriving indigo trade in the early medieval period. The indigo trade flourished further after the consolidation of the Abbasid Caliphate in West Asia in the eighth century CE and the resulting growth in Indian Ocean commerce. A detailed description of the dye-making process was recorded around the same time by the Roman writer Pliny the Elder, suggesting that indigo-dyed textiles were being traded across the Indian subcontinent, West Asia and around the Mediterranean sea. It appears later in Periplus of the Erythraean Sea, a navigational text from the first century CE. The earliest literary mention occurs in the Atharvaveda at the start of the first millennium BCE.

The earliest material evidence of indigo dye are traces found in textiles preserved in Egyptian tombs dating to the late Bronze Age. Fragments of fourteenth-century block-printed cloth from Gujarat found in Fustat, Egypt, as well as some later examples from the eighteenth century show that indigo was sometimes used for printing, although the method is unclear.

This method was typically used for dyeing whole sheets of fabric and was the prevalent method of using indigo in pre-colonial India. The dye bonds to the cloth in this altered state and returns to its deep blue shade after the cloth has been exposed to air and dried. The conventional dyeing method is to add a reducing agent such as zinc or ammonia to the hot dye bath in order to make indigo soluble - a state known as “white indigo” - before the cloth is dipped into it. Indigo powder is insoluble in water, acidic or alkaline solutions. The extraction process may be augmented with the addition of lime (Ca(OH)₂) to the first mixture of water and leaves and by dissolving various natural sugars into the paste. This deep blue paste is filtered for dirt and other impurities, pressed into cakes and dried for a few days, after which the indigo is ready to be used as a dye. The water and fine sediment at the bottom of the tank are allowed to settle for a day, after which the liquid is separated from the sediment. The upper portion of the mixture is drained out and used for irrigation, while the leaves are reused as fertiliser. Leaves are harvested before the flowers of the plant bloom and then soaked in water and churned until they release a navy blue froth. Indigo dye is extracted from the small, green leaves of the Indigofera plant. Apart from India, indigo has historically been grown and used in Southeast Asia, West Africa and the Caribbean. Indigo dye is typically produced in powder or cake form and sold either in this form or as a liquid suspension.

It played a major role in global economy through the medieval and colonial periods, until it was largely replaced in the late nineteenth century by a synthetic version of the dye. Due to the rarity of usable blue pigments in nature, indigo has historically been a prized good, used in the Indian subcontinent for dying textiles for local use as well as for international trade. Indigo%newline%A natural dye extracted from the Indigofera tinctoria plant native to South Asia, indigo dye is known for its deep blue colour and high potency compared to other blue dyes.

Indigo flower powder