Indigo: The Story of Blue Gold

Indigo is a deep blue dye extracted from the leaves of a variety of plants. It was not only a dye, but it has also been used as a pigment since ancient times. For centuries, Indigo was a valuable commodity that was traded across the globe, earning it the name ‘Blue Gold’. This article looks at the history of Indigo and its role in art, from Mayan artefacts to 17th-century European oil painting.

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Indigo: The Story of Blue Gold

What is Indigo?

The vast majority of blue pigments throughout history have been made from minerals, like natural Ultramarine Blue and Azurite, or from metal-containing compounds like Cobalt or Prussian Blue. Indigo stands apart because it is derived from plants. There are more than three hundred different plants that produce Indigo dye, but some of the most important have been Indigofera tinctoria (native to the Indian subcontinent), Persicaria tinctoria (found predominantly in East Asia), and Indigofera suffruticosa (a species that grows in Central and South America).

 

 

Chemically, the blue-producing compound we know as Indigo is called Indigotin. However, Indigo-producing plants do not actually contain indigotin. Instead, they contain a chemical precursor called indican. To extract the indican, the leaves are steeped in water and fermented. The fermentation process breaks down the indican into indoxyl and glucose. The mixture is then oxygenated by whisked it, which prompts molecules of indoxyl to combine to make indigotin. Indigotin is insoluble in water and sinks to the bottom of the solution where it can be dried out and pressed into cakes.

 

 

Indigo as a Dye

The earliest known evidence of Indigo dyeing is a piece of fabric found in Peru which is over 6000 years old. The use of Indigo also goes back to ancient times in India and West Africa, where the indigo plant Indigofera tinctoria, is easily cultivated. In Europe, blue dyes had been produced for thousands of years using woad (Isatis tinctoria), a plant that is native to the steppes and deserts of Asia but is easy to grow in colder climates. Woad contains the same blue compounds as Indigo but produces a weaker, less lightfast colour. Indian Indigo, extracted from Indigofera tinctoria, was known to produce a superior colour. In fact, the word ‘Indigo’ comes from the Greek indikon, meaning ‘from India’. Indigo and Indigo-dyed textiles from India were important commodities traded along the Silk Road during the Middle Ages.

When larger quantities of Indian Indigo began to enter the European market in the 16th century, it presented a threat to the local trade in woad. Guilds in England, France, and Germany imposed harsh sanctions (sometimes even the death penalty) on the import of ‘devil’ Indigo. In the 17th century, these regulations were relaxed, and as the demand for blue textiles grew, the European import of Indigo accelerated on a never-before-seen scale.

 

The Colonial History of Indigo

From the 16th century, Indigo plants were cultivated across European colonies in North and Central America. Like other colonial cash crops, slave labour was used to maximise yield and profit. Plantation owners also depended on the expertise of enslaved Africans, especially those from West Africa where Indigo had been cultivated and processed for centuries. The life expectancy of enslaved labourers at Indigo plantations was just five to seven years.

 

 

The North American Indigo industry collapsed during the Revolutionary War, but the British were already looking to the east. Indigo had been cultivated and used for dyeing in India for thousands of years, but over the 18th and 19th centuries, contract farmers in Bengal were coerced by the East India Company into growing Indigo for the British instead of food crops. The farmers were offered monetary advances, but it was not enough to cover the entire process of planting and harvesting, and the farmers were paid far below market value for their crop. When they could not pay back the loan, they were offered another advance to grow more Indigo, and so cycles of debt followed generations of farmers who could not get out of the exploitative contracts. These conditions led to the Indigo Revolt of 1859, when farmers in one Bengali district went on strike. This led to the Indigo Act of 1860, after which farmers could no longer be forced to grow the crop.

 

 

In the final years of the 19th century, a synthetic version of Indigo was introduced. From then on, the dye could be produced from aniline (derived from coal tar) entirely in a factory setting, at a fraction of the cost of the natural product. While this marked the rapid decline of the natural Indigo industry, it was also a big step towards dismantling systems that had, for centuries, exploited generations of people to meet the European demand for blue dye. Today, more than 5000 tonnes of synthetic Indigo is produced every year, and most of it is used in the production of jeans and other denim clothing. Natural Indigo is still cultivated and used for dyeing and painting, but it is on a much smaller, more sustainable scale than it once was. An example is Lutea, a paintmaking company based in Belgium who cultivate Indigo for their plant-based pigments and watercolours.

 

 

The History of Indigo in Painting

Natural Indigo is produced in cakes of pressed powder. When these cakes are ground up, the powder can be used as a painting pigment. While organic pigments made from dyes have generally poor lightfastness, Indigo does not fade as readily.

The history of painting with Indigo is very ancient. In India, Indigo was used as a pigment on paper and in murals since at least 2000 BC. It seems that the Ancient Greeks and Romans largely reserved Indian Indigo as a pigment, and used woad for dyeing.

 

 

While Indigo was known as ‘Blue Gold’, it has also been combined with real gold to create sumptuous manuscripts and scrolls. The famous ‘Blue Qu’ran’, which is written in gold lettering on Indigo-dyed paper, is considered to be one of the finest examples of Islamic calligraphy. Luxurious Buddhist scrolls produced in Japan, China, and Korea were illuminated with gold and silver, richly contrasted against a background of dark blue Indigo-dyed paper.

 

 

Indigo was the colouring agent in Maya Blue, a pigment used by pre-Columbian civilisations in Central America. They discovered a process of combining Indigo with palygorskite clay, likely using heat, which embedded the Indigo deep within the needle-like microstructure of the clay. The resulting pigment is extremely lightfast and chemically stable, so much so that it has survived centuries on objects and walls. It also appears that it was used in ritual practices. The process for making Maya Blue was lost after the Spanish colonisation, and for a long time its chemistry and why it is so permanent baffled the archaeologists and scientists who examined it. It is only in recent years that we have started to understand more about the pigment and the role that it played in pre-Columbian societies.

 

 

Over the 17th century, large quantities of Indigo were shipped to Holland by the Dutch East India Company, so it’s unsurprising that it was used frequently in Northern European oil painting. Because it is a deep, transparent pigment it was particularly useful as a glazing colour for blue drapery – which itself would have been dyed with Indigo.

 

 

As well as in painting, Indigo was also used by European artists in drawing. There are examples dating from the 15th century in which the pigment has been used to tone paper in preparation for silverpoint or ink drawings. In the below drawing on paper by Peter Paul Rubens, it has been applied as a wash to add tone and dimension.

 

 

Indigo remained a valuable commodity until the beginning of the 20th century. However, it fell out of favour in the artist palette in the 18th century when Prussian Blue was introduced. Prussian Blue is a similarly deep, moody blue, but was cheaper to produce and much stronger in colour.

 

Indigo Paints in the Modern Artist’s Palette

Indigo is a common colour found in paint ranges today. A small number are made with genuine Indigo, which is ideal for artists who want to explore the qualities of the real thing. Paints labelled with the pigment index number PB66 are made using synthetic Indigo, while those labelled as NB1 are made with natural Indigo.

 

 

Genuine Indigo is a beautiful colour. It is almost black in masstone, but washes out to a soft, muted sky blue. It is easy to see why the vibrant and punchy Prussian Blue came to replace Indigo, but looking at them side-by-side the older pigment has a greyish character that makes it particularly enigmatic.

 

 

The vast majority of paints that are called Indigo are not made with the genuine pigment, but are composed of different blue and black pigments which recreate the original colour. Although genuine Indigo has pretty good lightfastness compared to other organic plant-derived pigments, it still falls short of high modern standards, so these Indigo hues ensure that the colour will last. However, as you can see from the examples below, they vary greatly in hue.

 

 

Indigo is an extraordinary reminder of how ancient pigments and dyes have shaped cultures and histories, but it is important not to forget that the colour has been produced at an enormous human cost. Today, most people encounter a version of Indigo that is removed from the historical natural product – whether that’s synthetic Indigo used to dye our clothing or the ‘Indigo’ paints made with mixtures of blue and black pigments. However, the fact that it is still so present in our everyday lives is a testament to the enduring power of colour.

 

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Further Reading

What is the Best Non-Toxic Oil Painting Solvent?

Recreating the Colour Palette of Eric Ravilious

Fugitive Pigments: Why Do They Fade, and Does it Matter?

Review of Michael Harding Brick Lane Oil Colours

 

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