Colour analysis of some cobalt-based blue pigments

The coloring efficiency in different ceramic glazes of the classical Co olivine blue pigment (Co2SiO4) was compared with those obtained with a Co-doped willemite (Co0.05Zn1.95SiO4), and with a magnesium-doped Co-Al spinel (Mg0.2Co0.8Al2O4). The fired pigments and enameled samples were characterized by XRD, UV-VIS-NIR spectroscopy. CIE-L*a*b* color-measurements. and by SEM, EDX. The Co-olivine and Co-willemite pigments dissolved to a higher extent in the molten glazes than the Co-Al spinel. The darker blue color of the Co-olivine probed to be mostly due to Co2+ ions incorporated in the glassy matrix. Thr Co-willemite composition (which only contained a 1.3 Co wt.%) developed the bluest color hue of all pigments in both double and single firing glazes, while the magnesium-doped Co-Al spinel was found the most appropriate blue pigment in the bulk coloration of fast-fired porcelainized stoneware. (C) 2001 Elsevier Science Ltd. All rights reserved.