The Process, Continued - Firing
Probably the oldest method of firing is pit firing, in which a pot is placed in a pit dug into the ground or sand at a beach, lined with wood, and cooked like a barbecue. The pots aren’t glazed, but organic substances and chemicals can be thrown into the pit, and their fumes put random, interesting colors onto the surface of the pot.
Raku firing uses a typical gas or wood-fired kiln—usually a small one, but the method of firing is different. “Raku” is a Japanese family name and refers to the firing method developed by that family. It was brought to the west several decades ago, and modified somewhat.
With most other firing techniques the pots are brought to their final temperature over a 10-12 hour period, and then allowed to slowly cool in the kiln over an additional 12-15 hour period. A raku firing is much more dramatic—and risky! In a raku firing, the pot is brought to temperature (a relatively low temperature, around 1700 degrees Fahrenheit) very quickly (in an hour or less). Once the pot has reached the right temperature it is taken out of the kiln directly into the air by the potter who is wearing protective garb and handling the pot with metal tongs.
Imagine the stress on the pot to be dropped in temperature so radically, so fast! In the traditional Japanese firing, the pot is then dunked in cold water to arrest the development of the glazing by “setting” the glaze, or is simply allowed to sit. In the westernized version of the raku method, the pot is placed on top of flammable material, such as wood chips, and then covered with a metal can. The wood chips burst into flame, using up the oxygen under the metal can, and extracting oxygen from the glaze itself, which gives the surface glazing the lovely reduction effect.