Watercolor prepared with Egyptian Blue inorganic mineral pigment, chemically copper and carbonate silicate. This is the earliest synthetic pigment known: it was already produced during the IIIrd millennium a.C in Egypt. It production and use in art continued for centuries: in Egypt until the Ptolemaic period, in Minoan art, in Mesopotamia, in Greek civilization. Thanks to the Roman it spread from Pompeii to England and medioeval artists used it in fresco technique. To produce it, the following raw matters were mixed: sand, limestone, a copper mineral (usually malachite) and soda (sodium carbonate): the mixture was cooked at about 900°C for many hours. The resulting mass was ground and washed. In nature a mineral with the same composition does exist: cuprorivaite. It has a low tinting strength, it's really transparent and excellently lightfast.
Colouring agent: Copper calcium silicate