Unterglasur

Unterglasur, literally "under glaze," is a method of ceramic decoration in which the design is applied to the ceramic body before a glaze is added and fired. The decoration remains beneath the transparent glaze after firing, creating a durable, scratch-resistant surface with crisp outlines.

In practice, pigments or oxides are painted or stained onto the unfired or bisque-fired body. The piece is then coated with a glaze and fired at high temperature. The glaze fuses over the decoration, sealing it beneath the surface. This technique is commonly used on porcelain and fine stoneware.

The color palette for unterglasur work is defined by mineral pigments that survive high firing; cobalt blue (unterglasurblau) is historically the most important. Other colors come from iron oxides, manganese, copper, and related compounds, though the range is limited by glaze chemistry and firing conditions. The result is a design that remains stable and водorant to washing and abrasion.

Historically, unterglasur painting became a hallmark of European porcelain production from the 17th century onward, with Meissen and other centers such as Limoges and Delft contributing to its development. It is also found in East Asian porcelain traditions where underglaze blue and other pigments are used under a transparent glaze.

A related approach is aufglasur (overglaze) decoration, where the design is applied on top of an already glazed surface and fired again at a lower temperature. Unterglasur remains under the glaze and is valued for its durability and clarity of line.