Modelling clay is any of a group of malleable substances used in building and sculpting. The material compositions and production processes vary considerably.
Ceramic clays are water-based substances made from clay minerals and other raw materials. They are baked at high temperatures in a process known as firing to create ceramics, such as terra cotta, earthenware, stoneware, and porcelain. Paper clay produced by pottery clay manufacturers is a clay body to which a small percentage of processed cellulose fiber has been added. When kiln-fired, the paper burns out, leaving the clay body. Consequently, the firing temperatures and glazes selection should be the same on those used with the clay body.
Because the oils do not evaporate like water, oil-based clays remain malleable even when left in dry environments for long periods. Articles made from oil-based clays cannot be fired, and thus are not ceramics. Because rising temperature decreases oil viscosity, the malleability is influenced by heating or cooling the clay. Oil-based clay is not water-soluble. As it can be re-used, it is a popular material for animation artists who need to bend and move their models. It is available in a multitude of colors and is non-toxic. Readily worked in fine detail, oil-based clays are also suitable for the creation of detailed sculptures from which molds can be made. Castings and reproductions can then be produced from much more durable materials. Cars and airplanes may be created using industrial design-grade modelling clay.
Oil-based clays are referred to by a number of genericized trademarks.
Polymer clay is a modelling material that cures when heated from 129 to 135 °C (265 to 275 °F) for 15 minutes per 6 millimetres ( in) of thickness, and does not significantly shrink or change shape during the process. Despite being called "clay", it generally contains no clay minerals. Polymer clay is sold in craft, hobby, and art stores, and is used by artists, hobbyists, and children. Polymer clay is also popular in animation, since it allows static forms to be manipulated frame after frame. Leading brands of polymer clay include Fimo, Kato Polyclay, Sculpey, Modello and Crafty Argentina.
Paper clay is handmade or commercially available clay to which a small percentage of processed cellulose fiber is added. The fiber increases the tensile strength of the dry clay and enables dry-to-dry and wet-to-dry joins. Commercial paper clays air-dry to a firm, lightweight sculpture, with minimal shrinking during the drying process.
Paper clay can be used as an unfired body in craft and doll-making. It is used in ceramic art studios as sculptural and functional studio pottery.