Malayaite ceramic pigments prepared with galvanic sludge

The synthesis and characterisation of chrome-tin red malayaite Ca(Cr,Sn)SiO5 pigments are reported. The novel approach of using a galvanizing sludge from the Cr/Ni plating process as colouring agent is investigated. The ceramic pigments were prepared using a common, solid state reaction process, with optimisation of milling and firing conditions. Characterisation was undertaken using X-ray powder diffraction, diffuse reflectance spectroscopy and application in standard ceramic glazes. The ceramic pigments were of high purity (≥96% malayaite) and developed a burgundy colour due to the occurrence of Cr4+ and Cr3+ and also Ni2+ in the sludge-bearing samples. The hue of the pigments agreed with standard expectations and optimal formulations showed better performance than some commercial pigments, perhaps due to the contribution of nickel.