The origin of indigo
Indigo is held to be the world’s oldest textile dye. It’s also known as the living color that has a long history as it goes back centuries. Originally, the indigo pigment was first used in countries as China, India, and Japan. But, if you dive into the history, the oldest known fabric dyed in indigo already dates back to around 6,000 years ago which was discovered in Peru.
The word indigo comes from the Greek word indikon, which literally means from India.
The most common indigo pigment comes from the Indigofera Tinctoria plant. A plant that can grow from one to two meters high. As there are many plants that can be used to make indigo pigments, the Indigofera Tinctoria is the most used as it is known for its high-quality pigments that can be made of leaves.
Next to natural indigo from plants you can also use synthetic indigo, which is used mostly nowadays by coloring threads to weave fabrics for pair of jeans.
The magical indigo-dye process
During an indigo-dye process, the yarns are colored with indigo. Originally this was done by hand, hard labor-intensive, and also time-consuming. During a dye process the yarns are dipped in baths of indigo, the more you dip them, the darker blue the results are in the end.
When the yarns go into the green-ish indigo bath, and when they come out, the so-called magical process of indigo-dyeing starts. The green-ish-colored yarns come in contact with oxygen, and then they slowly turn into blue yarns. This is a very time-consuming process as most pairs of jeans that are made with yarns that are dyed go up to 12 times dipped in indigo.
Natural and synthetic indigo
Back in the days they only used natural indigo, but soon as the demand grew over time with mass production, they switched to synthetic indigo too. Synthetic indigo is a cheaper and less labor-intensive alternative used in production. Most of the jeans that are colored with indigo today are colored with synthetic indigo.
In 1865 the German chemist Adolf von Baeyer began working on the synthesis of indigo. He described his first synthesis of indigo in 1878 and the second synthesis in 1880. He created synthetic indigo that contained a better quantity of indigo and it was also easier to use for dyeing. This is because the qualities were more consistent compared to natural indigo.
Why jeans fade
Jeans and denim have always been synonymous with indigo. The warp of denim fabrics is dyed with indigo, while the filler of the fabric, the weft, is most of the time uncolored. You can easily see this when you flip your jeans, if you will see a natural colored cotton thread on the inside you know that your pair isn’t made with two colored indigo-dyed yarns, also known as double indigo.
The core of the blue yarns stays white in the dyeing process. So when you’re wearing and washing a pair of jeans the blue indigo will leave slowly the yarns and the white core is coming more through. This explains why you get these cool denim fades, and why jeans become lighter over time.