Pyrometric Cone

Pyrometric cones, also called witness cones, are devices used to gauge heatwork during the firing of ceramic materials in a kiln rather than to measure temperature by themselves. Sets of cones, usually three at a time, are placed in the kiln alongside the ware being fired, and because each cone in a set softens and bends over at a different point, the order in which they slump gives the potter a visual reading of when the ware has reached the combination of time and temperature it needs to mature. A pyrometric cone reading is described as a temperature equivalent rather than a simple temperature measurement, since it responds to accumulated heatwork across a firing rather than to a single instant the way a thermometer does.