Tonmasse

Tonmasse is a German term used in ceramics to denote a prepared body of clay used for forming ceramic wares. The term literally means clay mass; in English the equivalent term is clay body or ceramic body. The Tonmasse is the plastic, workable mass that is shaped before firing.

Composition typically includes clay minerals such as kaolin and ball clay to provide plasticity; silica (quartz) to form the vitrified matrix; fluxes such as feldspar or frits to promote melting during firing; and sometimes grog (calcined or crushed refractory) to control texture and drying shrinkage. Water content and particle size distribution influence plasticity and drying behavior. For porcelain, the body is highly refined with high-kaolin and low iron; stoneware uses more fluxes and coarser grog; earthenware relies on lower firing and contains more flux and porous body.

Firing results classify tonmasse into earthenware, stoneware, and porcelain categories, corresponding to different glaze compatibility and porosity. Tonmasse determines glaze fit and final appearance, including color and texture.

Preparation and testing involve mixing, wedging, and sometimes deflocculation for thin slip casting. Materials are evaluated for plasticity, drying rate, green strength, and shrinkage. In production, tonmasse quality control aims for consistent color, texture, and glaze compatibility to ensure reliable forming, casting, and firing outcomes.