Cone 9 Temperatures based on firing at 15°c, 60°c and 150°c based on an average temperature increase per hour
Orton Cones are a ceramic device that when heated in a kiln will bend, giving a value of ‘heat work’ which is a calculation of both temperature and time. A cone value is an accurate measurement of firing, giving information to the ceramicist that controllers/pyrometers alone would not produce. These can be used in oxidisation (electric kilns), gas and wood (reduction) and other fuelled kilns.
See PDF, giving general guidance and further information.
If I have a modern electric kiln with a controller, do I really need cones?
Cones do have their uses, so don't rule them out.
If you suspect your kiln is taking longer to fire than usual, you can use cones to make sure everything is working correctly. If you are getting glaze or clay problems, then using cones would be your first check to see if the equipment is at fault.
Cones tell you how much ‘heat work’ has been done in the kiln. ‘Heat work’ is a combination of both temperature and time. The controller on a kiln will tell you what temperature the kiln is at, or what temperature it is trying to get too. Intuition and guess work might tell you what cone firing you are roughly doing, but to be certain, use cones.
Note: In mid-sized to larger kilns there can be a heat differential between the top and the bottom of a kiln. Cones will indicate how even your firing environment is.