Cone Temperature Chart

For ceramics, kilns are not fired just to a temperature.  They are fired to a "cone" level, which accounts for time as well as temperature.  Think of it as heat absorption rather than just temperature.

Cone's come in different numbers, each of which corresponds to a heating-rate/temperature-combination which will make that cone deform.  At the beginning of the firing the cone is standing at an 8 degree angle.  A perfectly fire cone will be bent to a 90 degree angle.  If the cone is bent less, the kiln was under fired.  If the cone is bent more, the kiln was over fired.

Notice the way the cones are numbered.  The hottest is 10, going downward to 1.  Then as it continues to getting cooler it continues at 01, 02, etc.  So there is a BIG difference between cone 5 and cone 05!

Electric kilns with electronic controllers (such as the Skutt KilnMaster series) have a thermocouple which continuously measures the temperature, records it over time, and shuts off the kiln when the appropriate heat absorption has been met.  So if the ramping temperature is fast, the kiln will go to a higher temperature before it turns off than if the ramping temperature is slow (thus allowing the clay to absorb more heat along the way.)  The final temperature is most affected by the rate of temperature increase over the last 300 to 400 degrees of firing.

Note:  Think of the 0 in a cone number as meaning "minus".  So 06 is much cooler than 6 because it is like a "minus 6".