What is the difference between blue and indigo

Indigo - as blue as the jeans

The colored result only becomes really jeans blue after a series of chemical processes and when it is left to dry in the air.

The word "indigo" comes from Spanish and means something like "Indian". In the 15th century Vasco da Gama brought the Indian indigo to Europe, which was very popular with the French nobility.

Until then, people in this country had made do with a weaker coloring plant - woad. Although it does not belong to the indigo family, it provides a chemically identical dye.

Natural indigo pigments are not soluble in water. The coloring is therefore based on a reduction-oxidation process: Indigo must first be converted to indigo white by a reducing agent such as hydrosulfite in order to be able to dissolve in water.

The reduced indigo white penetrates the textile fiber, which now appears yellowish. If the substance is removed from the solution, the oxygen in the air oxidizes with the indigo white and converts it into blue indigo. Connected to the fiber, the color is now water-insoluble again.

When Vasco da Gama brought Asian indigo to Europe, woad cultivation went significantly downhill. It got even worse when the production of the dye no longer relied on natural raw materials. In 1897 Adolf Baeyer invented synthetic indigo.

The Badische Anilin- und Sodafabrik (BASF) in Ludwigshafen put this new dye on the market at a low price. However, it cannot replace the real indigo blue in terms of quality.