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CONES, cont.

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physical cones are not used. The kiln has an electronic controller that allows the ceramist to set temperatures and firing schedules. These use the same "Cone" designations as physical cones. To check the accuracy of the firing temperature of such kilns, though, some ceramists will put physical cones freestanding in various areas of the kiln (usually embedded in a piece of dry clay), placed so that they're visible through peepholes in the kiln's walls. These are called "witness" cones. By watching when the tip of the cone has softened, and falls down to the level of the base, the potter knows what temperature the kiln has reached.

2) Older electric kilns without electronic controllers may have a small 3-prong pincer inside the kiln. The cone is placed between the pincers and when it melts, the topmost pincer (which has been held up by the rigid cone) falls. In falling, the pincer trips the switch to shut off electricity to the kiln. So, by using the proper cone (each cone is designed to melt at a specific temperature), the kiln will shut itself off at just the right temperature.

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3) Gas kilns can also be used for biswque firing, though most ceramists use electric kilns. Some modern gas kilns have controllers that mimic the same functionality as the controllers in electric kilns. For gas kilns without controllers, the ceramist uses witness cones as described above.

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Glaze Firing

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Most pots are put through a second firing process after having glaze applied. This is called the "glaze firing". This glaze firing melts and chemically bonds the glaze or certain other surface decorations onto the work. Not all pots are put through a glaze 

firing. Some are left in their raw, unglazed state either for functional or aesthetic reasons, and some receive other kinds of surface treatments, like smoking and painting, rather than glazing.