Indigo has a huge and fascinating history that goes with this amazing dye.  Found on ancient fabric dyed indigo in Peru 6000 years ago it has woven into so many cultures throughout the world all with different varieties of plants making brilliant blue colour with fermented leaves.

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Indigo is often associated with Japan where it became well known in the Edo period when silk was banned for the commoners and Indigo was the only dye that would dye cotton. 

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Many plants can produce indigo but it is the Indigofera tinctoria from the Indian subcontinent that yields the best concentration of dye. 

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The chemistry of Indigo is just as interesting with its history. 

Indigo is a dark blue crystaline powder that is the sediment left after soaking and fermenting the leaves of the Indigofera plant. 

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To make the blue powder soluble, (in order to stay on the cloth), indigo pigment must be immersed in an alkaline solution and reduced (that is the oxygen must be removed), a process called ‘making an indigo vat’.  Soda ash makes the solution alkaline and Sodium Hydrosulphite removes the oxygen. This transforms the indigo into leuco-indigotin a yellowish soluble dye.

 

It is at this stage that you immerse the cloth in the indigo vat and leuco-indigotin attaches itself to the fibre. When you take the fibre out of the vat, leuco-indigotin combines with oxygen in the air to become indigo and fixes itself to the fibres. You see this happening as the colour changes from greenish yellow to blue.