Indigo is the colour that makes blue jeans blue.

The indigo colour originated in India. The name "indigo" comes from the Greek word "indikón", which in Latin became "indicum", and the meaning originally was simply "a fabric from India". Indigo is one of the very oldest dyes still in use today.

The history of indigo

Today, garments dyed with indigo are an essential part of our wardrobe: we all wear blue jeans. It is easy to forget that indigo used to be a rare commodity.

Just a few centuries ago, this exotic dye was so exclusive that only kings and aristocrats could afford it. It was painstakingly imported from distant colonies, giving indigo a status similar to tea, coffee, silk or even gold.

The use of indigo has been traced back 6,000 years by archaeologists, making it one of the oldest dyes still in use today. The oldest preserved textile fragments dyed with indigo were found in pyramids from the fifth dynasty of ancient Egypt.

Natural indigo

In South Asia, indigo pigment is traditionally extracted from the dry leaves of the Indigofera tinctoria plant - also known as "true indigo". This is actually today what we call "natural indigo". The colour is obtained through fermentation; a process of biochemical reactions produces an indigo sludge that can be then dried into blocks before being milled into powder.

In Europe, natural indigo was extracted from the woad plant, which has comparable properties to Indigofera tinctoria. The first textiles dyed with woad appeared in Europe in the 8th century BC, in the early Iron Age. For more than a thousand years, woad dominated in Europe. However, true indigo adheres better to less absorbent textiles such as cotton, so it became the preferred alternative.

Synthetic indigo

In the early days, indigo was "natural" because it was extracted from plants. These days, in contrast, almost all indigo is produced synthetically through chemical processing techniques. The raw chemical structure of synthetic indigo was discovered in 1878 by the German chemist Adolf von Baeyer. This was the first synthetic dye ever produced, and for this von Baeyer was awarded in 1905 with the Nobel Prize in Chemistry. In partnership with the Badische Anilin- & Soda-Fabrik (BASF), he worked on the further development of synthetic indigo for over three decades.

The result, which came on the market in 1897 as "Indigo Pure", was a phenomenal success.
Today, almost all blue denims are dyed with synthetic indigo.

Natural indigo vs. synthetic indigo

Let's explore the main differences between natural indigo and synthetic indigo.

Natural indigo is more expensive.
Not surprisingly, the main difference between the two is that synthetic indigo is much cheaper than natural indigo.
The price of synthetic indigo usually varies between $1 and $5 per 100 grams, while the price of natural indigo ranges from $20 to $40 per 100 grams. Prices can fluctuate even more for different grades and qualities.

To get an idea of what this means for the manufacturing cost of a pair of traditional jeans, multiply the price by the amount of indigo needed to dye the fabric blue. For a pair of 12 oz. denim jeans, for example, you would need approximately 25 grams of indigo.

The dyeing process

Although the process of turning green leaves into bright blue dye through fermentation has been practiced for thousands of years, it still has a magical effect. 

In the indigo dyeing process, the soluble, yellow-green indigo is dyed blue in the bath while it is still attached to the fiber. To do this, the wetted (but not dripping) fibre, yarn or fabric is immersed in the indigo bath and initially left below the surface for 5-10 minutes.

After dipping into the bath one or several times, different shades of blue can be produced. 

Each region - Mexico, Nigeria as well as Japan, for example - have their own spiritual rituals, recipes and techniques for making natural indigo dye. In India, the region of indigo's origin, the dye paste is dried into cakes to facilitate transport and trade. 
But since Levi Strauss dyed his first pair of jeans with indigo in 1873, the process has changed a lot.