Halide-Free Vanadium-Doped Zircon as Cyan Ceramic Pigment

A systematic characterisation of halide-free vanadium-doped zircon as a cyan ceramic pigment was carried out, focusing on its behaviour in glazes and under conditions of successive (accumulative) or direct firing, in comparison with a halide-mineralised sample. In accumulative firing at 1000 °C, the mineralised powder reaches more than 93% zircon, whereas the non-mineralised powder reaches only 70%. However, at low temperatures under direct firing, the reactivity of the mineralised sample is very low, with only around 7–8% zircon being formed, compared with the halide-free sample. The mineralised powder produces colourless powders at low temperatures and an intense blue colour at 1000 °C. In contrast, the halide-free samples change from yellow to green. However, their UV–Vis–NIR diffuse reflectance spectra show the same absorption bands. In glazing tests using different zirconia-free glazes, the highest blue b* values were obtained for the halide-free vanadium-doped zircon in both the alkali and ZnO–boron monoporosa glazes. Therefore, despite their yellow-green colouration as powders, halide-free vanadium-doped zircon pigments can be successfully used as turquoise ceramic pigments.