Formation and stability of Chinese barium copper-silicate pigments

Abstract

Experimental investigations were carried out on the synthesis of barium copper-silicate pigments by solid-state reactions. It was shown that the main factors that control the color tone of the different purple and blue pigments are kind and purity of raw materials, mixture ratio, nature of the flux used, heating, and temperature. There was a pronounced difference in reaction behavior between barium carbonate (BaCO3) and barium sulfate (BaSO4) as starting materials. Generally, the carbonate reacted much faster and at lower temperature than the sulfate. Han purple (BaCuSi2O6) was easier to obtain in pure form than Han blue (BaCuSi4O10), unless special fluxes were added. Han blue was thermally and chemically much more stable than Han purple. The poor resistance of Han purple to acids resulted in rapid fading and decomposition in striking contrast to the completely stable Han blue.