Colouring effects of synthetic inorganic cobalt-pigments in fast-fired porcelainized stoneware tiles

The paper reports a laboratory and industrial study on the rationalization of using synthetic cobalt oxide, aluminate and silicate pigments (0.5-4.0 wt%) for colouring porcelainized stoneware tiles. The addition of pigments to the base body in amounts up to about 1-2 wt% does not appreciably modify microstructure, nature and amount of phases of the fired tiles; while higher amounts, promoting liquid-phase formation, favour the sintering and can cause swelling of compact samples. On the basis of the results, inorganic cobalt-pigments seem very appropriate to produce coloured porcelainized stoneware tiles, but the better results are obtained by using CoO.AI(2)O(3). By controlling type and amount of pigment, it is possible to tailor different blue shades conferring to the product particularly interesting aesthetic effects.