What are cones?
Cones are little orange ceramic pyramids made from clay and glaze. Cones melt at specific temperatures indicating when to turn the kiln off at the end of a firing. Cones have numbers on them indicating at what intervals they will melt and bend. In a cone 10 firing you may use 3-4 cones. A guide cone, one or two numbers below your desired temperature, the desired temperature cone, and a guard cone to indicate if you have overfired. Cones must be placed in the kiln in front of a peep hole so you can see it while the kiln is firing.
When clay and glazes are fired the result depends on the rate of temperature rise and the time it is left at high temperatures as well as the temperature reached. If you just measure the temperature with a thermocouple, that does not tell you enough to get consistent results. Cones are specially formulated ceramics formed into triangular, pointy shapes. When placed in a kiln they will soften and bend (or “mature”) at a specific temperature ** when the temperature is increased at a specific rate **. If fired faster or slower, the cones will mature at a different temperature. Cones thus account for the firing history as well as the temperature. Cones with different numbers are made to mature at different temperatures. From lowest to highest temperatures the cones count from approximately 022, 021, 020 … 03, 02, 01 then to 1, 2, 3, and on upward. The “0” at the beginning is like a negative sign although there is no 0 cone. When firing by cones, typically three cones are used. The guide
