Pyrometric cones measure heat-work (the effect of time and temperature).
Pyrometric cones are slender pyramids made from about 100 carefully controlled compositions. Each cone number is unique in measuring temperature within a small temperature range (less than 30°C). Cones measure the amount of heat absorbed. As the cone nears its maturing range, it softens and the tip begins to bend, drawn down by the influence of gravity.
Orton also provides a computer program to relate bending behavior of cones to temperature, heating rate and hold time.
Large and Self-Supporting cones are used as witness cones to monitor the firing and verify temperature uniformity.