The ‘Blue Gold’ of India
Indigo is a dyestuff extracted from the indigo plant of the Indigofera genus which is indigenous to India. The Greeks called this blue pigment ‘indikon’, which translates into ‘a product from India’. This word then became Indigo in English. It is an ancient dye and there is evidence that it was in use from the third millennium BC. A frequently mentioned example is that of the blue stripes found in the borders of Egyptian linen mummy cloths from around 2400 BC.
The earliest example of indigo from Indigofera probably comes from the Harappan Civilization (3300 -1300 BC). Archaeologists also recovered remains of cloth dyed blue which dated back to 1750 BC from Mohenjo-Daro, now present day Sindh, Pakistan.
There are at least 50 different types of Indigofera in India. In the Northwest region, indigo has been processed into small cakes by producers for many centuries. It was exported through trade routes and reached Europe. Between 300 BC to 400 AD Greeks and Romans had small amounts of blue pigment in hard blocks, which they thought was of mineral origin. They considered it a luxury product and used it for paints, medicines and cosmetics.
In the late 13th century Marco Polo returned from his voyages through Asia and described how indigo was not a mineral, but in fact was extracted from plants. Small quantities of indigo were available in Europe then, but they were very expensive due to the long journey required and the taxes imposed by traders along the route.
The most widely recognised procedure of extracting Indigo colour is from either the leaves or the roots. However for reasons for sustainability, it is the leaves that are utilised more often than the roots.
The dye in the leaves doesn’t actually exist until it is manipulated. The chemical responsible for the dye is called indicant. The ancient practice of extracting indicant and converting it to indigo involves the fermentation of the leaves.
A complicated series of troughs and procedures are utilised to transform the Indicant into indigo dye.
First the leaves are matured by soaking them in water and causing them to ferment. At this stage the colour is removed from the leaves. This first round of fermentation takes around 14 hours, after which the liquid is drained into the second tank, a step down from the first.
The leaves are then removed and the solution which is then beaten and exposed in the air to oxidise the Indicant and transform it into indigo dye.
In the final trough, the mix is heated to halt the fermentation process.
The end result is filtered to remove any impurities and then dried to form a thick paste. This is the method by which the Indian people have been deriving indigo for thousands of years.
Excess water is poured off and the blue sludge is dried, after which, it is pressed into balls and left to dry. This is the conventional indigo colour powder.