Ceramic pigments for glazes are synthetic compounds with defined crystalline structures that are used for coloring engobes, glazes, crystallines for the ceramic industry and the arts. Inorganic ceramic pigments are very thermally and chemically stable pigments: they are in fact suitable to be used at high temperatures, and they resist very well to oxidizing or reducing actions and to the chemical aggression of molten glass.
The ceramic pigments for glazes are obtained from the solid-state reaction of metal oxides or salts at high temperature, generally in the presence of mineralisers such as alkali metal halides. Solid-state reactions that occur in the temperature range between 800 and 1400 ° C and can occur in discontinuous furnaces, muffles, or continuous, rotary ovens.
The crystal structures that are formed during the reaction in the solid-state depend on the metal oxides that make up the pigment and are for example garnet, olivine, spinel, rutile, zircon, corundum, sphene.
Ceramic enamel pigments due to their poor solubility, introduced into the enamel remain dispersed and unchanged, even after cooking. They improve the aesthetic appearance of the glass, giving it a color and do not give rise to defects such as bubbles or holes. The stability and colorimetric yield of the color always depends on the base used and on the thermal cycle used. There are pigments more suitable for low temperatures and others more suitable for high temperatures. Moreover, the chemical composition of the vitrifiable base has a noticeable effect on the development of the color of the glaze.
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