Pyrometric Cones are little triangular or pyramid-shaped pieces of clay (witness cones) that are placed in the kiln before it is fired. Each melts at a certain rate of temperate “cone” and is observed (witnessed) through the kiln’s peep holes in order to assess what temperature has been reached. (heat-work)
Potters say their piece, clay or glaze is “cone 10”. Which means for it to fully mature (or melted in the case of glaze) it needs to reach a temperature of 2381 F over a measure of time and the combination of the temp and time is what gives you heat work.
When I use the witness cones in my kiln on each shelf. At the end of my firing I can tell which part of the kiln was hotter or cooler depending on how much the witness cone has slumped-over during the firing. It slumps less where the kiln is cooler and slumps more where the kiln is hotter.
My kiln has a computer; so I don’t have what’s called a kiln sitter. This is a little device that holds a special little “cone” that will melt or slump and fall during the firing to turn the kiln off when it reaches the desire temperature.
I’ve prepared a cone firing chart for your reference. Please note that the temps go UP from 022 to 15. To me, this is the most confusing thing about kilns and knowing about their temps 022 is hotter than 021, 06 is hotter than 05 etc… until you get to “1” and then 6 is hotter than 5, 10 is hotter than 9 etc. So, that -0- (zero) on the front of your temperature measurement changes what your talking about in temperature completely.
For instance; “06” (Cone 06 is 1855 Fahrenheit, but “6” (Cone 6) is 2269 Fahrenheit. If you use a clay that is rated only for cone 06 in a cone 6 firing; you’re going to have a disturbing, melted glob that used to be your labor-intensive piece on your kiln shelf or floor at the end of your firing; and that can be heartbreaking and expensive.