Pyrometric cones have been used since the late 1800's to monitor the kilns performance. Originally thought to be temperature indicators, studies in 1926 showed that time & atmosphere also affects cone bending behavior.

Orton is the only manufacturer in the united states that makes pyrometric cones.

Large and self supporting cones are used as witness cones to monitor the firing and often are used to to decide when the firing is complete.

Small cones and pyrometric bars are used in the kiln-sitter (R), a mechanical switch that cuts off the power in electric kilns.

Small cones are occasionally used as witness cones, but caution is recommended, since these shorter cones require slightly higher temperatures to bend, as compared to large or self supporting cones.

Cones are still needed when a kiln is equipped with an electronic controller. Electronic controllers allow the kiln to be heated to a temperature. Controllers use a thermocouple to sense temperature. These change with time and ware, causing the kiln to fire hotter than desired. Witness cones placed on the shelf near the outside edge will check weather the controller is firing accurately.

The number representing the cone firing temperature is engraved on the side of every cone in every box to avoid confusion and mistakes in firing. So read the cone to make sure its the right cone temperature you need to fire.

  Witness cones    Small bars      Small cones    Lg. regular cones

The following are approximate temperatures for firing at medium speed of 270 degrees per hour for self supporting cones. Your temperature may vary by the condition of the kiln.

cone 022- 1094   cone 021-1143   cone 020-1180  cone 019-1283 cone 06-1855      cone 05-1911     cone 04-1971   cone 03-2019

The following are approximate temperatures for firing at medium speed of 270 degrees per hour for small bars and cones. Your temperature may vary by the condition of the kiln.

cone 019-1279    cone 018-1350   cone 017-1402  cone 016-1461 cone 06-1852      cone 05-1915     cone 04-1958    cone 03-2014

                                          Cone plaque

       Sm. bar               Sm. cone           Lg. cone     self supporting/witness 

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Imagine  that the witness cone is a clock. If it points straight up and didn't bend, its too cool. If it bends to around three to six o'clock it's a good  firing and if it gets past six o'clock  or it starts to melt, its in the too hot range.

Items on this page are all available on our site click here