Synthesis of Sphene-pink Pigment under Various Firing Conditions

The present research was performed to determine the optimal firing condition and holding time for malayaite crystal, which is responsible for the stable pink-red coloration in glaze at high temperatures, using CrCl₃ as chromophore for the synthesis of Cr₂O₃-SnO₂-CaO-SiO₂ system pigments. The malayaite crystal was influenced by the raw materials used for synthesis, firing temperature, and holding time. Thus there are differences in the crystal phase and in the coloration according to the condition of synthesis. When CrCl₃ was used as chromophore, the pigment could be synthesized at lower temperatures, because CrCl₃ melts at 1150℃, which is much lower than the temperature at which Cr₂O₃ melts (higher than 2435℃). And the employed Cr ion showed a change in oxidation state. When a mineralizer was used to improve the employment of malayaite and the Cr ion, and the low temperature was maintained at which the malayaite crystal is produced, the production of malayaite crystal was promoted and the employment of chromophore was also promoted in the oxidation state of Cr (IV). The results of the experiment showed that the optimal firing condition was 18 h of holding time at 800℃, using CrCl₃ as chromophore, followed by 2 h at the raised temperature of 1150℃. The change in coloration of the Cr (IV) employed by malayaite showed a very rich color of red. Thus it was possible to effectively synthesize sphene-pink pigments with more red tint at a low temperature.