Love Letters to Indigo

December 30, 2021

Yagiz Pekkaya

3 minute reading

Three Quarters Blue, One Quarters Purple

How old would you think a man-made color could be? Perhaps our first question should be ‘what is one of the oldest colors produced by humans?’ Without keeping you waiting any longer, we can say that indigo blue, which gives denim that iconic color, leads the list.

First and foremost we must imply that Indigo is not a naturally occurring dye. It must be artificially processed from the naturally occurring precursors indican and isatan.

The dye is extracted from the leaves of plants in the genus Indigofera, which grow in tropical climates. Dyers made dye by crushing the plant leaves and fermenting them in water. This turns the compound indican, which is a colorless amino acid, into indigotin, a blue dye. The fermented leaves are then mixed with lye, pressed into cakes, dried, and finally powdered.

In principle the production of indigo is a simple process, although the underlying chemistry is complex. However in practice it is very difficult to produce a deep blue dye. Consequently in many societies, from Central Asia to Indonesia, indigo dyeing has always been a specialist craft, with secret protocols jealously guarded and passed down from generation to generation. Today in countries like Indonesia there are only a few good indigo dyers and indigo dyeing, unlike morinda dyeing, is an expensive process.

The Early History of Indigo

Indigo may have been used as a dye since the early Neolithic, although at present, evidence of its earliest use comes from a 6,200-year-old cotton fragment found at the site of Huaca Prieta in Peru (Claro et al 2016). Other early finds from the Indus Valley and the Egyptian Nile date to the third millennium BC, while finds from China date to the second millennium BC.

Synthetic indigo – indigotin – was developed in Germany and launched commercially in 1897. It had a major impact on the production of natural indigo, devastating the indigo plantation industry in British India within a decade.

Although synthetic indigotin is chemically identical to the indigotin found in naturally derived indigo, it lacks the secondary pigments such as the red-coloured indirubin and yellow-coloured kaemferol, which give natural indigo its complex and attractive hue. 

Synthetic indigo also lacks the botanical impurities that initiate micro-crystal clustering, a phenomena that creates a deeper blue along with a degree of iridescence.

Use of Indigo in Denim

Original denim was dyed with dye from plant Indigofera tinctoria. Modern denim is dyed with synthetic indigo. Denim is often dyed with indigo and dried many times over to get a stronger color that will not fade quickly.

Despite many other blue dyestuffs, indigo has kept its popularity for denim dyeing. This no doubt is achieved by the fact that indigo has several properties that have not yet been achieved by another single dyestuff. The unique feature of indigo dyed denim is the possibility of achieving wash down effects on repeated washing without losing the freshness of the color. Another important feature of indigo is that unlike many other dyes, indigo dyed denim does not pose health hazards. In fact, indigo is so safe for living things that it has long been used to color polyester medical sutures. Indigo is also used as food color and as a medical indicator applied intravenously.

Indigo was not just a commercial success as a dye but a color that some think can inspire particular moods or qualities. It’s said that those with an “indigo aura” have great intuition and a profound inner awareness. Duke Ellington even called one of his jazz pieces “Mood Indigo.” We will leave it up to you to see if indigo can inspire your creativity!