Production and characterisation of iron-chromium pigments and their interactions with transparent glazes

In this study, production and characterisation of pigments by using less expensive raw materials such as limonite and chromite was undertaken. The resulting pigments were characterised by using X-ray diffraction (XRD) and UV-Vis spectrophotometer. The colour of glazed tiles containing 3 wt.% pigment change from dark brown to light brown depending on the calcination temperature and limonite content. With pigments prepared with 50% limonite content calcined at 1250 °C, the chocolate brown colour was obtained corresponding to the commercial brown pigments. An iron-chromium black pigment was synthesised from a mixture of pure chromium (III) oxide (Cr₂O₃) and iron (III) oxide (Fe₂O₃) powders and was used to determine possible interactions between a pigment and a transparent glaze. The interactions were studied using a scanning electron microscope (SEM) attached with an energy dispersive X-ray spectrometer (EDX). The results showed that black pigment particles give brown colour to the glaze. EDX analysis on pigment crystals embedded in the glaze clearly showed that Zn and Mg diffused into pigment crystals and caused a change of colour from black to brown.