What is a Cone? A Guide to Pyrometric Cones and Kilns

Ceramic ware is most often fired to a “Cone” as opposed to a temperature. Your ceramic ware provider can provide guidance on which cone to fire to for your specific ware.

Pyrometric cones are designed to deform at certain moments during a firing. This deforming action allows the kiln to shut off automatically at the proper point (as in the case of the mini bar and Kiln Sitter) or simply to record what happened during the firing (as in the case of the witness cone).

The exact moment the cone deforms depends primarily upon two factors: time and temperature. The temperature present at the moment "cone" is achieved depends upon the rate of temperature increase.

With this simple concept in mind it's easy to understand why "cone" and temperature are not the same thing. For a proper cone firing, time and temperature must always be considered.

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Pyrometric Cone Chart

Please note that the Cone Chart gives 3 different temperatures for each cone number. As discussed above, the equivalent cone temperature depends upon how fast one gets to it. Generally speaking, the temperatures in the 108°F/Hour column are used when discussing ceramics, porcelain and china.