Glazuren

Glazuren, or glazing, in ceramics refers to the vitreous coating applied to pottery and ceramic objects. The glaze, fused during firing, forms a glassy layer that seals the porous clay body, provides color and decoration, and increases durability and moisture resistance. Glazes are typically composed of silica as the glass former, with fluxes to lower the melting temperature and alumina to stabilize the glass network. Additional materials include colorants and opacifiers, such as tin oxide for white, cobalt or copper for blue and green, and zirconia as needed.

Glazes vary in transparency and finish, from transparent to opaque, glossy to matte, and are formulated for different firing ranges: low-fire, mid-range, and high-fire. Tin-opacified glazes produce an opaque white surface; many modern glazes are lead-free. Applications include dipping, brushing, spraying, or pouring onto bisqueware or leather-hard ware. After application, the piece is fired to maturity, during which the glaze fuses to form a durable surface. Under-glaze colors are applied before glaze, while overglaze enamels are applied after glaze firing, sometimes with a second, lower-temperature firing for decoration.

Glaze defects can occur, such as crazing (fine cracks), pinholing (holes), crawling (patchy glaze), blistering, or fisheyes, depending on glaze composition, firing, and compatibility with the clay body. Proper formulation and firing schedules are essential to match the glaze to the ceramic substrate and achieve the intended aesthetic and functional performance. Glazing is a central step in ceramic production, shaping both appearance and durability.