Physical Processes Involved in Production of the Ancient Pigment, Egyptian Blue

Abstract

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.