Pigments Used in Glass and Ceramics
Ceramic pigments are inorganic compounds with a crystalline structure, known for their outstanding thermal stability and resistance to molten glass. They are widely used in coloring ceramic glazes, clay bodies, and enamels, as well as in producing vibrant colors for tiles, glass, porcelain, and other ceramics. These pigments feature a robust thermally stable structure integrated with specific chromophore components, delivering the desired hues.
The color stability of ceramic pigments is influenced by several factors, including their crystalline structure, firing temperature, firing speed, the chemical composition of the material being colored, milling techniques, and the kiln atmosphere. These variables affect the pigment's performance, so conducting field tests to verify application properties is highly recommended. Most ceramic pigments are stable at firing temperatures of 1200°C to 1250°C, though in materials with a lower content of non-aggressive glassy phases, their stability may exceed this range.
Depending on the application, pigments can be used directly by mixing them with water or added as colorants in clay bodies and glazes. While some pigments are formulated specifically for clay bodies, others may not be suitable. In clay applications, pigments are often used in engobes or slips to coat the surface rather than coloring the entire body. An exception is the use of stains for tinting porcelain in neriage techniques.
When used in glazes, typically in concentrations of 1–10%, additional care is needed because certain pigments may react with materials in the glaze. Factors such as the presence or absence of boron, zinc, calcium, and magnesia can affect the final result. Manufacturers typically provide detailed information about these interactions. Although most pigments are compatible with both oxidation and reduction atmospheres, some are limited to specific maximum temperatures, which can also be confirmed through manufacturer guidelines.
To expand the range of available colors, pigments can often be blended to create new shades. However, black pigments are an exception, as they cannot produce gray tones. Black pigments are typically composed of multiple metallic oxides, and at lower concentrations, the final color reflects the dominant oxide within the black pigment.
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