In this study, Ni and Co-gahnite pigments were produced from Al2O3 powder and ZnO powder obtained from industrial metal slags. Different pigment compositions were prepared by adding metal oxides (NiO or Co3O4) and mineralisers (NaF, CaF2 or Li2CO3). Pigments were calcined in an electric furnace at 1300, 1400 and 1450 degrees C for 4 h at a heating rate of 2 K center dot minute(-1). The pigment powders obtained were added to a transparent ceramic glaze and to porcelainised tile bodies. The pigment colours were determined using L*a*b* measurements from a spectrometer. On one hand, the results show that Ni-gahnite pigment is not useful for industrial applications because it has poor colour intensities and stabilities. On the other hand, our results also show that Co-gahnite pigments can be produced using ZnO from industrial metal slags, and that they have an intense blue colour.

Keywords: Colour; Gahnite; Spinels; ZnO; Powders-solid state reaction; Pigment