Pyrometric cone

Pyrometric cones are pyrometric devices that are used to gauge heatwork during the firing of ceramic materials in a kiln. The cones, often used in sets of three, are positioned in a kiln with the wares to be fired and, because the individual cones in a set soften and fall over at different temperatures, they provide a visual indication of when the wares have reached a required state of maturity, a combination of time and temperature.

Pyrometric cones give a temperature equivalent; they are not simple temperature-measuring devices. They were especially important historically, before devices for measuring actual kiln temperatures had been developed.