These bowls are made from a talc:ball clay mix, they are used for calcining Alberta and Ravenscrag Slips (each holds about one pound of powder). The one on the right was bisque fired to cone 04 (about 1950F). The one on the left was fired to only 1000F (540C, barely red heat), yet it is sintered and is impervious to water (strong enough to use for our calcining operations). That means that there is potential, in many production situations, to bisque a lot lower (and save energy). Primitive cultures made all their ware a very low temperatures. Tin foil melts at 660C (1220F) yet can be used on campfires for cooking (so the temperatures of primitive wares would have been low indeed).
A densification process occurring within a ceramic kiln. With increasing temperatures particles pack tighter and tighter together, bonding more and more into a stronger and stronger matrix.
Potters and some manufacturers fire ceramic ware twice, once to prepare it for glazing (call bisquit firing) and the second time to melt the glaze onto it.
The use of some traditional firing techniques is still popular among modern potters and sculptors (who are accustomed electric and gas kilns, often with computer controllers).
Plainsman Electric Bisque Firing Schedule
Three-step to 1832F