overglazes

Overglazes, also known as overglaze decorations or on-glaze enamels, are transparent or opaque pigmented layers applied to a ceramic piece after the primary glaze has been fired. They are typically formulated from finely ground colorants, glass frit, and various fluxes that melt at lower temperatures than those required for the base glaze. Because they are applied over a vitrified surface, overglazes do not affect the piece’s structural integrity and can be used to add intricate patterns, pictorial scenes, or subtle shading.

The application of overglaze can be done with a brush, spray, sponge, or screen printing, allowing for a wide range of artistic techniques. Once the decorative layer is applied, the piece is refired, usually in a kiln at temperatures between 700 °C and 950 °C (1300 °F–1740 °F). This second firing, known as the “overglaze firing” or “muffle firing,” fuses the pigments to the glazed surface without fully remelting the underlying glaze, preserving the original glaze texture and color.

Overglazes are favored for their versatility and the ability to correct or enhance work after the main glaze has set. They are common in decorative pottery, porcelain, and studio ceramics, as well as in commercial tableware where detailed designs are required. Limitations include lower durability compared to underglaze decoration and potential for wear in high‑use items. The technique dates back to early Chinese porcelain, where transparent enamels were used to embellish jade‑like wares, and it spread throughout Europe during the 18th century. Modern formulations continue to expand colour ranges and firing options for contemporary ceramic artists.