Indigo dye is extracted from the small green leaves of the Indigofera plant. The leaves are harvested before the plant flowers, then soaked in water and churned until they release a navy blue foam. The upper part of the mixture is drained and used for irrigation, while the leaves are reused as fertilizer. Water and fine sediment at the bottom of the tank can settle for a day, after which the liquid is separated from the sediment. This dark 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 extraction process can be augmented with the addition of lime (Ca(OH)₂) to the first mixture of water and leaves and dissolving various natural sugars into the dough.
Indigo powder is insoluble in water, acid or alkaline solutions. The classic dyeing method is to add a reducing agent such as zinc or ammonia to the hot dye bath in order to make the indigo soluble – a state known as “white indigo” – before the fabric is dipped in it. The dye binds to the fabric in this altered state and returns to its dark blue hue after the fabric has been exposed to air and dried. This method was generally used to dye whole sheets of cloth and was the common method of using indigo in pre-colonial India. Fragments of 14th-century block-printed fabric from Gujarat found in Fustat, Egypt, as well as later 18th-century examples show that indigo was sometimes used for printing, although the method is unclear.
The earliest material evidence of indigo dyeing are traces found in textiles preserved in Egyptian tombs dating from the late Bronze Age. The first literary mention occurs in the Atharvaveda at the beginning of the first millennium BCE. He later appears in Eritrea sea voyage, a navigational text from the first century CE. 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 traded across the Indian subcontinent, l Western Asia and around the Mediterranean Sea.
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The indigo trade flourished further after the consolidation of the Abbasid Caliphate in West Asia in the 8th century CE and the consequent growth of trade in the Indian Ocean. The genizah documents – a set of over four hundred thousand documents found in Fustat, Egypt, containing commercial and administrative records from the 9th to the 19th centuries – suggest a flourishing trade in indigo during the early medieval period. The documents even used the Sanskrit word for indigo, nilias a suffix for the names of some Arab merchants who traded in dye.
Sanjan, a port in Gujarat that exported indigo, was a key crossroads in early medieval trade networks. By the late medieval period, Kabul, Afghanistan, Aleppo, Syria, and Jeddah had also become major nodes, distributing indigo to Central Asia and Persia, Ottoman Turkey, and the eastern seaboard. of Africa, respectively.
French and British involvement in the trade took place in the Levant, where indigo prices were set for Mediterranean markets and, by extension, the rest of Europe. Although a very expensive dye, indigo frequently surpassed local European dyes such as pastel due to its potency and fastness, leading to it being repeatedly banned between the 16th and 18th centuries in France, Norway and Great Britain.
For most of the medieval period, parts of present-day Gujarat, Rajasthan, and coastal Pakistan produced the bulk of the subcontinent’s indigo. From the 16th century, the mercantile enterprises of the Portugese Estado da India and the British and Dutch East India Companies traded in indigo from these regions. Production then shifted to Bengal when the British East India Company became a ruling power in the region.
British policies in Bengal, such as the Tinkathia system, required landowners to cultivate indigo in at least three Kathas (a unit of land measurement) in each grandha (1 bigha = 20 kathas) of their land. These landowners (or indigo planters, as they were called then) secured the services of agricultural laborers who were often brought in to cultivate Indigofera instead of food crops. While British indigo planters and traders made huge profits exporting indigo to Europe and Britain, workers were poorly paid and forced into debt, sometimes even starving. Indigo plantations were also established in other colonies using similar policies, particularly in the West Indies. During the Indigo Revolt of 1859, farmers in Chaugacha and other parts of Bengal staged a violent uprising against planters and zamindars. The human toll of indigo cultivation, particularly in Bengal, has since been remembered as a symbol of colonial exploitation.
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At the end of the 19th century, Badische Anilin- und Soda-Fabrik (BASF), a chemical factory in Germany, developed and began mass production of synthetic indigo. In 1914, natural indigo accounted for only 4% of global indigo use, and despite minor revivals, it continues to have a niche presence today. The vast majority of indigo is now synthetic and is used to dye denim, although some natural indigo continues to be produced in southern India, particularly Karnataka.
More recently, freeze-dried indigo in its crystalline reduced state has become commercially available, greatly shortening the dyeing process due to its water solubility. In addition to being used as a dye, indigo can be reacted with sulfuric acid to form a salt which is used as a dye for food and pharmaceutical products.
This excerpt is taken from MAP Academy’s “Encyclopedia of Art” with permission.
The MAP Academy is a platform that strives to transform the way South Asian art histories are viewed, taught and discussed – both regionally and globally. Created and maintained by over 40 scholars, editors and academic advisors from around the world, it comprises the first ever encyclopedia of art from the Indian subcontinent – beginning with over 2,000 articles and definitions, and growing continuously.