underglaze

Underglaze is a decorative coating applied to ceramic surfaces before the piece is fired in a kiln. It serves multiple purposes, primarily as a protective layer that prevents the glaze from adhering directly to the clay body during firing. Without underglaze, the glaze would melt and fuse with the clay, potentially causing uneven surfaces or poor adhesion. Underglazes are typically composed of mineral pigments suspended in a liquid binder, often water or a solvent-based medium, which allows them to be applied smoothly to the ceramic surface.

The primary function of underglaze is to provide a base for decorative designs. Once the piece is fired, the underglaze hardens and becomes part of the ceramic body, allowing artists to create intricate patterns, colors, and textures. Common types of underglazes include oxide-based pigments (such as cobalt blue, iron oxide red, or chromium green) and metallic oxides (like copper for blues and greens). These pigments can be applied using various techniques, including brushwork, sponging, stamping, or even airbrushing, depending on the desired effect.

Underglazes are fired at temperatures typically ranging from 1,200 to 1,600 degrees Fahrenheit (650 to 870 degrees Celsius), depending on the ceramic material and the specific underglaze formulation. After firing, the underglaze becomes opaque and chemically bonded to the clay, forming a durable layer that resists wear and stains. Some underglazes may also provide a slight gloss or matte finish, enhancing the overall appearance of the ceramic piece.

In addition to decorative purposes, underglazes can also serve functional roles, such as providing a barrier against moisture or chemicals in certain applications. They are widely used in pottery, porcelain, and other ceramic arts, making them an essential component in the production of handcrafted and mass-produced ceramic goods. Proper application and firing techniques are crucial to ensure the underglaze performs as intended, contributing to the quality and longevity of the finished piece.