Jeans are often referred to by their colour. We call them “blue jeans.”
But did you know that the blue colour in blue jeans has been used to dye clothes for thousands of years? And have you noticed how the colour changes as you wear and wash your jeans?
It’s called ‘fading’—and it’s because of the way denim is dyed that it happens. In this lesson, you’ll learn how denim is dyed.
Dyeing is the process of adding colour to the yarn. It’s done by soaking the yarn—or a woven fabric—in a liquid that contains a dyestuff.
The classic kind of denim that is blue on the outside and white on the inside is ‘yarn dyed’—only the warp yarn is dyed while the weft is left natural or bleached. For solid colour denim, fabric dyeing is often used.
Indigo is a vat dye. To get the dyestuff onto the yarn or the fabric, it’s solubilised in water with the help of a reducing agent.
When the yarn or fabric is pulled out of the dyeing vat, and gets in contact with the atmospheric oxygen, the oxidation process binds the colour molecules to the fibres of the yarn.
The reason denim fades is the modern dyeing process. It gives what’s known as a ‘ring dye effect.’ The colour doesn’t reach the core of the yarn. The dyestuff only binds externally. As the dye slowly wears and washes off, the undyed core appears.
When you buy a pair of raw denim jeans, there’s still have some starch left in fabric from the sizing process. Combined with the tightness of the weave, this is what gives raw denim its stiffness.
In the in-depth member resource about indigo dyeing, you can learn more about the types of dyes used for denim and two dyeing methods.
The History of Indigo
Today, indigo-dyed garments are an integral part of everyone’s wardrobe—whether you’re a construction worker or a banker, a minister or a rock star, a toddler or an old man.
It’s easy to forget that indigo used to be a rare commodity. Only a few centuries back, this mysterious dyestuff was so exclusive that only royalty and the aristocracy could afford it. It was imported with great difficulty from far-off colonies, which earned indigo a status similar to that of tea, coffee, silk or even gold.
144 years ago, a Bavarian immigrant patented the very first pair of blue jeans, and introduced them to the world. The global success story of the dark blue worker’s trousers made of durable denim is relatively well known. But what about their continuously changing blue colour, which has persistently fascinated us humans for such a long time?
Heritage Post editor, Mathias Lösel, asks and answers that question in issue no. 21 of the German cult magazine for rugged men’s culture.
Indigo’s Origins …
Indigo’s name gives its origin away: it simply means ‘the Indian’ or ‘from India.’ But we now know that, besides India, indigo is also endemic to the tropical zones in Africa and China.
As early as more than 5,000 years ago, our ancestors in India, East Asia and Egypt, as well as probably the Maya, used the blue dye derived from the Indigofera Tinctoria plant to dye their clothes.
They must have really adored the deep blue, almost violet shade that could be produced with the help of this plant—otherwise, they would not have gone through the very demanding process necessary to achieve it.
… and How Natural Indigo Is Made
To start with, the harvested leaves of the Indigofera plant have to be soaked in water to let the indican (an amino acid) contained therein release glucose.
The freed indican soon starts to ferment with the other plant enzymes. As a result, the water turns yellow after several days. The product of this fermentation process is called indoxyl and as it is left to dry in the air, oxidises and coagulates into the blue indigo.
This, in turn, is mixed with an alkaline solution (usually they would have used bicarbonate of soda) and the resulting sludge is then pressed into cakes and dried. The hard cakes finally could be ground into a fine powder which contained the much-coveted dark blue pigment.
While the production of indigo dye was an arduous process, importing it to the European royal courts, where the beautiful blue was in such high demand, was even more cumbersome and above all expensive.
Woad and Indigo’s Bastard Sibling
Since growing the Indigofera plant in Europe was impossible due to the cooler climate, from the 12th century onward, the Isatis Tinctoria plant, also called woad, which could be cultivated in temperate regions, was grown instead.
The dye derived from this plant gives similar results. However, while the production of this dye was equally arduous and time-consuming as for the Indigofera dye, the amounts needed for dying cloth were far less favourable:
Given equal amounts of plant material, woad only yields one-thirtieth of the amount gained from Indigofera, which made dyers continue their search for a more profitable alternative.
Finally, in the 17th century, the indigo enthusiasts of the time found what they were seeking in the American colonies. Settlers there had managed to cultivate a direct relative of the Indigofera plant in the more favourable hot and humid climate of South Carolina, Amorpha Fruticosa, also called false, or bastard, indigo.
The Origin of the Names “Jeans” and “Denim”
During the 18th century, the trade republic of Genoa became the largest buyer of this bastard indigo dye and traded dyed cotton and linen throughout Europe, particularly to England and France.
What made Genoa famous was a sturdy, deep blue cotton cloth, ideally suited to making tough work clothes for fishermen, seamen, dock workers and miners. Since French was widely spoken throughout Europe at that time, the cloth was named ‘Bleu de Gênes’ (the blue of Genoa), which would later devolve into the English derivative ‘jeans.’
The majority of this Bleu de Gênes cloth was exported to the French town of Nîmes, which was then the European metropolis of weavers and ribbon makers.
To lessen their dependence on the Italian cloth manufacturers, the weavers in Nîmes soon began experimenting with producing their own blue cloth, which was similarly robust and durable.
Made from wool and raw silk, they developed the twill cloth, made with a pattern of diagonal parallel ribs, for which they used two different threads: The warp yarn was dyed with indigo, the weft yarn was left white.
The resulting cloth had two markedly different sides. The side that showed more warp yarn became the outward-facing, dark blue side, while the light blue side with its majority of visible weft yarn was the back.
The cloth was very durable due to its special weaving technique, and it was in no way inferior to the Italian Bleu de Gênes. Soon, the French cloth had its own name: Tenue de Nîmes (Clothes from Nîmes), short de Nîmes, which the English and Americans eventually turned into the now world-famous ‘denim.’
Growing Demand and How Indigo Was Synthesised
As a result, demand for indigo continued to be as strong as ever. However, the pressure to find cheaper alternatives to the complex production process of the plant dye grew exponentially with demand.
This was further expiated by the great American Gold Rush, and the associated burgeoning demand for work clothes, which in turn skyrocketed the demand for indigo in the US.
At the end of the 1860s, German chemist Adolf von Baeyer undertook his first experiments in an attempt to develop an artificial indigo.
Over the following years, he went on to create a synthetic production method, which–severely simplified–went like this: Starting with the amino acid aniline, he produced the plant ash oxindol. This is reduced with the help of zinc dust into indol, which in turn is reduced into its derivative isatin.
When Baeyer finally managed to completely isolate the isatin, he had found the first wholly synthetic alternative to natural indigo, which possessed similarly excellent dye properties.
Meanwhile, demand for the deep blue dye had risen to new heights. Even though the Gold Rush was almost over by this time, the increasing industrialisation of Europe and America with its manufacturers, factories, mines, shipbuilding docks, and oil production meant that hitherto unheard of numbers of workers suddenly needed sturdy workwear.
In 1873, Jacob W. Davis and Levi Strauss patented a pair of work trousers that would go on to conquer the world. The jeans made of durable denim with rivet reinforced pockets quickly become fast favourites among the hardworking men.
Thus, indigo blue, which had once been a luxury reserved for royalty and the aristocracy had finally completed its transition into the distinctive mark of the working classes.
The Commercialisation of Indigo Dyeing
The end of the 19th century brought with it the first boom of modern chemistry giants like BASF and Hoechst, who were investing heavily into the development of further synthetic alternatives to the continuously highly coveted blue dye.
In 1897, Hoechst and BASF had their own version of synthetic indigo patented and began commercial production in increasingly large amounts.
In 1904, both companies signed a so-called indigo agreement and simplified the isatin production process further, resulting in a more consistent and stronger dye.
Less than a decade later, the production of synthetic indigo had almost completely replaced the naturally derived indigo dye from the Indigofera plant on the world market. Only India went on producing indigo from purely natural sources until around the beginning of the First World War.
Today, there are very few producers that offer natural indigo dyed jeans to their customers. The dye for these is usually imported from either Brazil or El Salvador, where the Indigofera plant is still cultivated in small amounts. However, naturally dyed jeans are generally of a lighter blue than the synthetically dyed ones.
Apart from rare exceptions, denim cloth is nowadays solely dyed with synthetic indigo; colour saturation and purity are far superior to natural indigo, and its production is far easier, cheaper and environmentally friendlier.
But our love affair with the mysterious dark blue colour is still going strong. Even more than 5,000 years after its discovery, we humans are still enthralled by indigo and wear it almost every day. And observe with fascination how the colour changes continuously, fades, ages and wears away. Just like us.