Mixed-Metal Oxide Pigments and Ceramic Colorants

4 Mixed-Metal Oxide Pigments and Ceramic Colorants 

Colored mixed-metal oxide pigments result from the incorporation of color-giving transition metal ions into an oxide host-lattice (see Table 5.9-13). Depending upon the particle size and properties of the chosen host, pigments (0.2 to 2 pm) or ceramic colorants (stains) (up to ca. 10 pm) result, which in many cases are characterized by high thermal and chemical stability and thus are suitable for the coloring of enamels and ceramics. 

Mixed-metal oxide pigments and ceramic colorants (stains)  

The starting materials in the manufacture of mixed-metal oxide pigments (as a rule carbonates, hydroxides, oxides and oxide-hydrates) are intimately mixed and heated, if necessary with added flux, at temperatures of 1000 to 1300°C. The particle size can be controlled, and thus the coloristic properties influenced, by varying the calcination temperature and the added flux. The 0.2 to 2 pm particles required for the pigment sector are obtained by intensive grinding of the calcined clinker in ball or sand mills. 

Stains and oxides (ceramic colorants) with an average particle size up to ca. 10 pm and a broad particle size distribution, are in some cases manufactured at still higher temperature, up to 1400°C. The higher primary particle sizes are necessary because a more or less strong solubilization of the particles takes place during the firing of the enamel or ceramic frits. The component to be enameled or glazed is coated with a mixture of intensively mixed frits and colorants then fired at temperatures between 500 and 1200°C. 

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