CHEMICAL STATE OF CHROMIUM IN TIN-SPHENE.

Heating of the mixture of CaCO//3, SnO//2, SiO//2 and Cr//2O//3 developed reddish color simultaneously with the formation of tin-sphene (CaO multiplied by (times) SnO//2 multiplied by (times) SiO//2). Characterization of chromium in tin-sphene by chemical analysis, ESCA and ESR revealed that the chromium was mostly tetravalent. ESR and chemical analyses of vanadium in tin-sphene showed that the vanadium was also mostly tetravalent, substituting for the Sn**4** plus in the tetragonally distorted octahedral symmetry. It was pointed out that the only one board absorption band in the visible region observed in the reflectance spectra of a chrome-tin pink stain would be caused by Cr**4** plus in this distorted octahedral symmetry. Furthermore, chemical states of chromium and tin in glazes containing calcium were studied by ESR and ESCA in connection with the glaze colors.