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 common solid state reaction process, with optimisation of milling and firing conditions. Characterisation was done by 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 complied with standard expectations, and optimal formulations showed better performance than some commercial pigments also tested for comparison, perhaps due to the contribution of nickel.