The Indigo pigment has been popular in artists’ circles since the early days of European history, first among the Romans and later, particularly between the 14th and 19th centuries, in the rest of Europe. The blue colour was originally extracted naturally from plants containing the dye Indigotine, but this changed when the German chemist Adolf van Baeyer developed a synthetic alternative during the Industrial Revolution. These days, Indigo is made from pigments with an excellent lightfastness.
The pigment’s name comes from the Greek word Indikon or ‘paint stuff from India.’ Before the process was synthesized, Europeans derived the pigment from the leaves of the Woad plant, which were ground and then soaked in vats of hot water until they fermented. This process released a sweet-smelling dye that coloured the water yellow. The plant remains were then filtered out and the water transferred to shallow basins. By slapping the water with sticks, oxygen was introduced, initiating a chemical reaction. This resulted in a blue sediment forming on the sides and the bottom of the basin. This sediment was scraped off, formed into cakes and left to dry. In order to make paint, these cakes were ground and then mixed with a binding agent such as egg or wax.
Colouring textile, on the other hand, was certainly a less fragrant process. The cakes first needed to be soaked in tubs filled with water, bran and urine, which resulted in the necessary yellow solution. The textile was then added to this solution, usually on a Saturday, and then hung up to dry until Monday. Due to the oxygen from the air, the blue colour returned. This is also where the term ‘Blue Monday’ derives from. Colouring textile in this manner was done in blue dyeworks, which was at the time a huge, flourishing trade in England, the Low Countries, France and Thüringen in Germany. However, at the end of the 15th century, the Portuguese explorer Vasco da Gama discovered a plant in Asia that contained 30x more blue than Woad. This plant was given the name Indigofera Tinctoria and the blue that was extracted from it Indigo. Despite fierce attempts to prevent (and even prohibit under penalty of death) imports, Da Gama’s discovery heralded the end of the lucrative Woad era.
ADOLF VON BAEYER’S SYNTHETIC INDIGO
During the Industrial Revolution, German chemist Adolf von Baeyer managed to analyze and subsequently synthesize Indigo. In 1915, he developed a method of production that eliminated the need for the Indigo plant. But this pigment introduced by Von Baeyer has since also been superseded, as its lightfastness left a lot to be desired. Today, the Indigo in Rembrandt water colour is made using a combination of two pigments that produce a lightfastness of at least a hundred years under museum conditions.
THERE IS NO ACCOUNTING FOR BLUE
Indigo blue cannot really be defined, as it greatly depended on the type and quality of the plants from which it was extracted. In his book ‘Schilderkunst, materiaal en techniek’ (‘The Art of Painting, material and technique’) Max Doerner writes that the shade is similar to Berlin blue. Physicist Isaac Newton, on the other hand, placed the tone in the spectrum between blue and violet. Rembrandt water colours have opted for a darker Indigo, which tends towards green.
Royal Talens has the colour Indigo in the following product ranges:
Rembrandt oil colours, colour number: 533
Rembrandt water colours, colour number: 533
Van Gogh water colours, colour number: 533
Amsterdam acrylic colours Expert Series, colour number: 533