glazes

Glazes are coatings that form a glassy or glossy surface on objects, most commonly on pottery, but also in glassmaking and culinary contexts. In ceramics, a glaze is a vitreous layer fused to a ceramic piece by firing. It serves decorative purposes, provides a watertight surface, and can alter color and texture.

Most ceramic glazes are suspensions of silica in a glass-forming base with fluxes that lower the melting point and stabilizers that reduce crazing. Silicon dioxide forms the glassy matrix; alumina stabilizes the glaze; fluxes such as feldspars, borates, or lead historically reduce melting temperatures and adjust viscosity. Color is introduced by metal oxides and stains such as copper oxides (greens and reds), cobalt (blue), iron (brown/amber), and manganese. Glazes are formulated for compatibility with a given clay body to control thermal expansion and prevent defects.

Glazes are applied by dipping, pouring, brushing, or spraying, and then fired in a kiln at temperatures appropriate to the clay and glaze system. Common firing ranges include low-fire, mid-range, and high-fire. Proper glaze fit is essential to prevent crazing, shivering, pinholes, or devitrification, which can occur if the glaze expands or contracts differently from the ceramic body during cooling.

Glazes are categorized by finish as transparent, opaque, or matte. Decoration can occur as underglaze colors applied before a clear glaze, overglaze enamels fired after a glaze, or tin-based opacified glazes such as majolica. In culinary contexts, glazes refer to viscous coatings applied to foods to impart sheen, flavor, and moisture retention.