Egyptian blue
Composition and Properties of Egyptian Blue
Egyptian blue is an artificial copper calcium silicate with the assumed chemical formula of CaCuSi4O10. The actual composition of samples found at ancient sites varies considerably. It is the oldest synthetic pigment known to Man and its composition, properties, and color are similar to Han blue (BaCuSi2O6) known in imperial China. The mineral cuprorivaite has the same composition but was never used as a pigment.The pigment is chemically completely stable in all media and is absolutely lightfast. There are no known incompatibilities with other pigments.
Names
Pompeian blue, Alexandrian blue, Pozzuoli blue, blue fritPB 31, CI 77437Named after Ancient Egypt where it was first produced around 3100 B.C.
Preparation
The pigment can be prepared by heating a mixture of a calcium compound (carbonate, sulfate or hydroxide), copper compound (oxide or malachite) and quartz or silica gel in proportions that correspond to a ratio of 4 SiO2 : 1 CaO : 1 CuO to a temperature of 900°C using a flux of sodium carbonate, potassium carbonate or borax. The mixture is then maintained at a temperature of 800°C for a period ranging from 10 to 100 hours.Note: This recipe does not correspond to the ancient production method of Egyptian blue.
History of Use
The pigment has been in use since the early dynasties of ancient Egypt beginning around 3100 BC (1-3). It was also found in paintings in ancient Greece, India, and Rome. Recently it was identified in medieval and even in Renaissance paintings (4,5).
Quote
Side by side with the production of metals, the Egyptians and the inhabitants of Mesopotamia perfected the arts of making glazed pottery... and the production of glass. ...vessels were baked in tall closed furnaces. "Egyptian blue" was made in Egypt by heating silica with malachite and lime... applied with soda as a blue glaze on faience, and the blue glass is also colored with copper. Some early... Egyptian and Babylonian blue glass are coloured with cobalt.
Source: J. R. Partington
