indigotin

In a new study, researchers picked up signals of the chemical compounds indigotin and indirubin, the key components of indigo dye, they report today in Science Advances.

The stamps are usually covered with a black ink made of sulphate of iron, and this is fixed by myrobalans; the Nīlgars usually dye a plain blue with indigotin.

The colouring principle of indigo is a body named indigotin, to which the formula C16H16N2O2 has been given.

To neutralise this purple effect, a small quantity of a yellow dyestuff and a trifle of indigotin are added.