The Process, Continued - Firing
2) The second way in which cones are set up is to place them freestanding in the kiln (usually embedded in a piece of clay), placed so that they're visible through peepholes. 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.
In lieu of using cones, some potters use electronic controllers which measure the temperature through a probe in the kiln. More expensive kilns are equipped with electronic kiln controllers that govern temperature without the use of cones.
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.
Types of Kilns
Kilns can be electric, natural gas or propane-fired, wood-fired, sawdust-fired, and probably fired using almost any other energy source imaginable. Temperatures inside the kiln can be determined by experience based on the color of the heated kiln, by using an electronic temperature gauge or controller, or by using pyrometric cones, described below.