Obtaining blue pigments from the indigo plant

Before chemists, particularly those of the 19ᵉ century, got to grips with the manufacture of blue, this color was rare in its natural state. Although mineral pigments such as lapis lazuli were already known, they were difficult to obtain and were mainly located in a few restricted regions of the planet, mainly in Afghanistan, making it a rare and extremely expensive pigment. It was therefore mainly thanks to mastery of the extraction of dyes from indigo plants that we were able to obtain this color.

The first traces of indigo cultivation date back to around 4,000 BC in India. The Mesopotamians and Egyptians of ancient Egypt also mastered the cultivation of this plant, since traces have been discovered dating back to around 2,500 BC. Indigo's first appearance in print dates back to 77 A.D., in the book "De materia medica" by the Greek physician, pharmacologist and botanist Dioscorides. The Mayans of pre-Columbian America used indigo by mixing it with palygorskite clay to obtain a blue close to primary blue, called "Mayan blue".

In Europe, it was another indigo plant that made the fortunes of many traders, particularly in and around Toulouse: Isatis Tinctoria, better known as Pastel des teinturiers. Initially, this plant was not classified in the indigo family, but research has shown that its components are the same as those found in other plants in this family.

On their arrival in Asia in the 16th century, the Portuguese discovered that indigo was also present, and that it was sold on the markets in powder form.