Here are just a few facts that I’ve found:
Indigo is different from all other natural dyes (apart from shellfish purple) in that it needs no mordant. It is insoluble and is deposited on fibers as microscopic particles without needing to form a chemical bond with them.
Indigo has been used for dyeing cloth throughout history and for many centuries was used primarily in those climates where it could be grown, such as in India, Indonesia, Japan, China, Egypt, Africa, Central and South America.
There is evidence of indigo dyed cloth with Egyptian mummies going back 5000 years and blue was the predominant colour in the funeral wardrobe of Tutankhamen. Blue is the only colour found in the earliest dyed linen fragments of ancient Israel and Palestine. The linen urns containing the Dead Sea scrolls carried symbolic patterns in blue. Babylonian texts talked of garments dyed in blue and there is even a tablet housed in the British Museum that has recipes and methods for dyeing in indigo. The bible talks of 'blue clothes' being traded by the merchants of Sheba. Blue silk fragments of the 3rd millennium BC have been found in China and the Chinese character for "ai-" indigo has been found in records dating back to the 1st century AD and as early as the Western Zhou Dynasty (1045-711BC) a system of dyeing techniques was developed. Indigo has also been used in tattoos in places from Java to Nigeria and bodies discovered in the UK which are thought to be from 300 BC may have been covered in blue tattoos. - possibly indigo?
Indigo was produced from many plants throughout the history but the most famous indigo dye was produced from the plants of the Indigofera. One of those plants is Indigofera tinctoria which is native to India which was the earliest major center for production and processing of indigo dye. From there it arrived to Ancient Greece and Rome where it was considered a luxury product. Although other Asian countries like China, Japan and South East Asian nations also used indigo for centuries, India is considered to be the oldest centre of indigo dyeing. Even its name points to that with the Greek word for the dye, indikón - meaning 'Indian'. Romans changed that to indicum and then into English as the word “indigo”. Another ancient term for the dye is ‘nili’ from the Sanskrit meaning dark blue from which the Arabic term for blue ‘al-nil’ is derived.
Romans used indigo painting and for medicinal and in cosmetics. In the Middle Ages indigo became rare because of heavy duties imposed by Persian and Greek merchants. Instead of it people used woad, a dye made from the plant “Isatis tinctoria” that was chemically identical to the indigo but didn't have the strength of colour that indigo had.
In the second half of the 15th century the Portuguese discovered a sea way to India which opened a trade route to India, the Spice Islands, China and Japan. After that use of indigo became very popular in Europe. But when European powers like the French planted indigo plantations in their tropical colonies in the West Indies, imports from India significantly declined as it was cheaper to get it from elsewhere in the east.
However this easily obtainable indigo threatened local woad industry in Europe so France and Germany outlawed imported indigo in the 16th century with the French Government even attaching the death penalty to the use of indigo rather than woad and in England the woad lobbyists got indigo certified as poisonous plant and had it banned until 1660. In reality indigo continued to be used - often in combination with woad with most supplies coming from the French colonies. Around 1745 the English were at war with the French, so they had to look elsewhere for their indigo supplies and it was at this time that a woman called Eliza Lucas Pickney started the first indigo plantations in the US and by 1755 the US were exporting nearly 500 tonnes of indigo to England. It said that at the time of the America revolution, the US dollar was worthless and indigo cakes were used as currency.
Early in the 19th century the UK turned back to India for indigo. As the English were not allowed to own more than a few acres they had to persuade farmers to grow indigo instead of rice, this overtime lead to great unrest and riots as farmers were forced into growing more indigo to feed the need of the English for indigo. Its said that Mahatma Gandhi’s first act of civil disobedience was in 1917 when he went to support indigo peasant farmers and laborers.
The chemical properties of indigo dye remained baffling well into the 19th century. It was so mysterious and challenging to work with that, in many cultures, folklore arose around the dyeing process. In Bhutan, pregnant women were not allowed near the vat in case the unborn baby stole the blues, and women in Morocco believed the only way to deal with a particularly challenging vat was to start telling outrageous lies.
In 1897, Johann van Baeyer from Germany, developed a synthetic indigo for which he won the Nobel Prize for chemistry in 1905. The synthetic indigo could be produced in a lab with a consistent quality and a price that was competitive with natural indigo. Within 10 years the production of natural indigo had dropped 90 percent. While maintaining all the characteristics of natural indigo, today most of the world’s indigo is synthetic.