underglazeis

Underglazes are colored ceramic coatings applied to a pottery surface before a transparent glaze is added and the piece is fired. They are designed to show through the final glaze, producing sharp lines, even color, and detailed imagery on a range of clay bodies. Unlike overglazes, which are painted on top of a fired glaze, underglazes must be fired at the same time as the glaze and are formulated to fuse with the glaze during the glaze firing.

Underglazes come as ready-to-use liquids or as powders mixed with water. They can be opaque or semi-opaque and are often formulated to be compatible with specific firing ranges, from low-fire bisque to high-fire stoneware. Their appearance can vary from matte to glossy once the clear glaze is applied. They are typically used on bisque-fired ware or leather-hard clay and can be applied with brushes, sponges, stamps, or through inlay techniques such as Mishima or sgraffito.

Techniques for applying underglazes include line drawing, block coloring, stippling, and tracing through stencils. After decoration, a clear glaze is applied and the piece is fired to its maturation temperature. The clear glaze seals the color, adds gloss, and can alter the perceived intensity of the underglaze color, depending on glaze chemistry and firing conditions.

Historically, underglazes have been central to many ceramic traditions, including Chinese underglaze blue and modern studio practice. Today they are widely used in both hobbyist and professional ceramics, with a range of formulations for low- and high-fire processes and for different aesthetic outcomes. Modern underglazes are generally lead-free and designed for predictable results across compatible glaze systems.