Physical Processes Involved in Production of the Ancient Pigment

Egyptian blue, which was the first synthetic pigment to be used in antiquity, consists of crystals of calcium-copper tetrasilicate (i.e. cuprorivaite (CaCuSi 4 O 10 )). The physical processes associated with the formation of Egyptian blue were investigated by high-temperature X-ray diffraction measurements on synthetic mixtures of quartz, malachite, and calcium carbonate. The high-brilliance, high-energy radiation ID15B beamline at the European Synchrotron Radiation Facility was necessary to ensure good time/temperature resolution, penetration, and high-quality data. The results established that the Egyptian blue crystals are formed through nucleation and growth within a liquid or glass phase, even for mixtures with an alkali content as low as 0.3 wt% soda. Furthermore, the microstructures observed in a scanning electron microscope indicated the ancient Egyptian blue pigments were produced from mixtures containing several weight percent of alkali.