Prior to the firing, students glaze their pieces and the kiln, still warm from the last round of firing, is loaded. The heating process is driven by a propane burner, and when preheated, a kiln such as this takes half an hour to reach temperature. At around 1800 degrees farenheit, the oxygen supply is cut off and a reduction process--during which the metal oxides in the glazes are robbed of their oxygen to produce the spectacular metallic finishes that characterize raku ware--begins.
The fiber upper kiln is removed, and the pots are quickly transferred to cans filled with sawdust, leaves, or newspaper before they re-oxidize. The cans are then sealed and the reduction process continues. Alternatively, as shown below, light colored pieces may be treated with ferric chloride to produce a golden finish.
After 5 minutes, the pots are removed from the cans, quenched in water, and then filled with water to prevent the glazes from reoxidizing--the water in their interiors will continue to boil violently for some time. Some pots, particularly those of large diameter or inconsistent thickness are destroyed by stress from differential cooling and dimensional changes, but most survive. When the pieces have cooled, the work can immediately be examined and with a little cleaning, is finished barely an hour after beginning. This is a great reduction from the 24 hour cycle of a typical firing.
