These Self Supporting Orton Pyrometric Cones are used on a shelf inside a kiln to determine when a firing is complete, if the kiln provided enough heat or if there was a problem during the firing. This style of cone does not require a cone holder. These Orton cones are made from carefully controlled compositions so that they bend in a repeatable manner over a very small temperature range. When the cone tip reaches a point level with the base it indicates it is properly fired.