Glasieren

Glasieren, or glazing in ceramics, is the process of applying a glaze to pottery to create a glassy, protective coating that is fused to the surface during firing. Glazes serve functional roles—reducing porosity, sealing the ware against liquids and stains, and improving mechanical strength—as well as decorative ones, providing color, gloss, texture, and surface effects.

Glazes are suspensions of silica, alumina, and fluxes in water, often with colorants such as metal oxides. They can be transparent, opaque, matte, or crystalline. The glaze is typically applied to bisque-fired pottery, though some pieces may be glazed on greenware. Common methods include dipping, brushing, pouring, and spraying, sometimes followed by multiple coats or decorative applications.

After application, wares are fired in a kiln to a temperature appropriate for the glaze and body. This is called glaze firing. The glaze fuses into a glassy layer as the ware reaches peak temperature. Color and texture are influenced by glaze chemistry and firing atmosphere (oxidizing or reducing). Temperature ranges are commonly described by cone numbers: low-fire (about cones 04–06), mid-fire (cones 4–6), and high-fire (cones 9–10), though exact numbers vary with materials.

Glazes can present defects such as crawling (uneven spreading), pinholing (surface holes), crazing (network of cracks due to thermal expansion mismatch), or shivering (glaze peeling). Proper glaze development and test tiles help minimize these issues. The term underglaze refers to decoration applied before a transparent glaze; overglaze decoration is applied atop a fired glaze.

Safety: many traditional glazes contain heavy metals; modern commercial glazes are often lead-free, but handling and disposal should follow safety guidelines.