Spotlight on Indigo


Isaac Newton, when describing the colour spectrum of a rainbow, listed 7 colours: Red, Orange, Yellow, Green, Blue, Indigo and Violet. But today Indigo often gets left off this list of rainbow colours; leaving the 3 primary and 3 secondary colours we are familiar with. 

The colour Indigo is named after Indigo Dye extracted from the plant Indigofera Tinctoria.

Initially Indigo was created from plants that were cut and packed into large vats where it softened and fermented. The dark precipitate was then skimmed, strained, pressed and dried into cakes which formed the basis of Indigo. This pigment is the natural plant-based pigment used for dyeing clothes which fades over time and is not to be confused with the synthetic pigment.

Indigo is one of the oldest dyes for textile dyeing with countries such as India, Japan, Egypt and Peru using this dye for centuries and dating as far back as ancient Mayan civilisations in pottery and frescoes. In the 19th century this blue dye was exported from India to Europe at the rate of thousands of chests per year for clothes dyeing purposes, including the French Army who wore dark blue indigo uniforms during the French Revolution, as a more robust and practical colour than white. Indigo dye continues to be used for clothing, especially denim, and in fact is lauded for its fading qualities in jeans adding depth to the texture. 

The colour of Indigo in the form of a dye however is a different colour from Newton’s ‘spectrum’ Indigo or Indigo in pigment form. As a pigment its lightfastness, it did not match the more permanent and expensive Ultramarine mineral blues.

William Perkin at age 18 was the first to create a modern synthetic dye. In 1856, while he was experimenting with creating a synthetic version of Quinine (the medicine used for treating Malaria), he yielded a black solid in a failed attempt to produce this, but on cleaning the flask he noticed a bright purple liquid which he dipped a piece of silk into and noticed that this left a permanent mauve dye on the material. His curiosity in doing this may have been fuelled by the fact that Perkin, a chemist, had once had dreams of being an artist.

This discovery opened up new possibilities for colourmen and 30 years later in 1878, German chemist Von Baeyer discovered how to synthesis Indigo. Following this discovery, the commerce of natural Indigo declined and high-quality synthetic Indigo is now used for pigments.

In 1997 when the Shakespeare Globe theatre was reconstructed in London, Indigo was used to paint the heavens of the theatre.