A formulation design and preparation of gold‐free purple of Cassius based on the doped malayaite.

Malayaite (CaSnSiO5) doped with Cr may be used as a cheap gold‐free purple red pigment to substitute the purple of Cassius. Different molar ratios of Ca/Sn malayaite doped with Cr were prepared and various characrizations were employed. The results indicate that the pigment is composed of CaSnSiO5 and SnO2 when the molar ratio of Ca/Sn is 0.8, and the color is close to agate red color. When the molar ratio of Ca/Sn is 1.25, the phases CaSnSiO5, SnO2, and Ca3SnSi2O9 exist simultaneously, while the color is yellow or yellowish colors. Excessive Ca(II) increases the normal calcination temperature of pigment, from 1080°C to 1130°C. The distribution of chromium ions on the sample surface varies greatly with the change in Ca/Sn molar ratio. The theoretical formulation was obtained based on the stoichiometric formula of CaCrxSn1–xSiO5 by using response surface methodology (RSM). According to the RSM model, the relationship between the molar ratio of Cr/Sn/Ca and the color property was established. The desired pigment formulation (rendering agate red) color is that the molar ratio of Cr/Sn/Ca is 0.010:1.003:0.800. The accuracy of the models was confirmed with analysis of variance, the simulation results were verified again by experiments. [ABSTRACT FROM AUTHOR]