Pyrometric cones

Ceramic clay wedges placed inside a kiln before firing. (Bar shapes are also available.) At a certain temperature a cone will bend, so by constant observation it can be determined at what point particular temperatures are reached in the kiln. Used in a Kiln-Sitter, electricity is turned off to the kiln when the cone placed in it bends. The E. Orton Jr. Ceramic Foundation advises using a particular set of temperature equivalents for their cones, which melt at 34 different temperatures, each identified with its own cone number: starting at 022 at the lowest temperature (1157 degrees F.), continuing to cone 01, then to cone 1, and to the hotest at cone 12 (about 2420 degrees). Orton cones come in two regular sizes, temperatures varying between them slightly, rarely significantly. Number 06 large regular cones bend at 1830 degrees F., and small regular cones at 1873. Number 04 large regular cones bend at 1940, and small regular cones at 2008. Clay must be fired at a higher temperature to bisque than any subsequent firing for glazes. A triangle is often used as a glyph for "cone."