THE RAKU PROCESS
by Paul Soldner
Firing of raku is basic and simple. The bisqued pots are decorated in the usual manner with stains, engobes, resists, or textural treatments. They are then glazed with low melting glazes such as lead, borax, or frit bases.
Water added to the pot in the glazing process must be driven off by thorough drying over the exterior of a hot kiln before proceeding with the firing.
The pot is seized with long-handled tongs and thrust directly into the preheated red hot kiln. It is allowed to remain there until the glaze melts, as observed through the peephole. Time required for this melt may vary from a few minutes to an hour or more according to the kiln temperature, thickness of glaze, type of glaze, and the thickness of the vessel walls.
After firing, subtlety of color may be produced by subsequent reduction smoking of the pot. The red hot pot is placed in a covered vessel containing combustible materials. The pot may also be dropped directly into cold water for the purpose of creating an oxidized effect or to freeze the molten state of the glaze. If the pot is quite large, it is safer to cool it more slowly in a tight container which may or may not contain smoke producing materials.
Raku firing offers the potter many advantages over other firing techniques. Some of these are simplicity, low fire reduction, the resultant somewhat insulated body, and spontaneous effects. Very important is the potter's attitude and involvement in the firing cycle. The intimacy and immediacy are never more deeply felt in any other ceramic process.
Any kiln will do. It is only necessary to obtain a moderate heat (about 1600 to 2000 F.). The kiln should open and close fast so that pottery can be withdrawn without too much heat loss.
from Leach, A Potter's Book:
white lead 66%
gerstley borate 80%
gerstley borate 30
Commercial low fire glazes can also be used.