To explain the Raku process we must first state that most all other types of ceramics are loaded into a cold kiln where the firing proceeds slowly until the desired temperature is reached. This firing cycle may take anywhere from 8-24 hours or even longer. When the kiln has reached temperature it is shut off and allowed to cool enough to be able to remove the ware using bare, or lightly gloved hands. The cooling cycle may last from 12-24 hours or longer. The piece is considered finished once it is taken from the kiln.
In Raku, the pieces may be loaded into a cold kiln but are often preheated and loaded into a hot kiln. The firing proceeds at a rapid pace with the wares ‘reaching temperature’ (approx. 1800 degrees) in a cycle that may be as short as 15-20 minutes. Glaze maturity is judged by the trained eye without the use of cones or measuring devices. When the firing is completed the wares are immediately removed from the kiln. At this point the glaze is molten; tongs or other lifting devices are used for this move.
The wares are now subjected to a "post firing reduction" phase. These pieces are put into a sand pit with a combination of combustible materials such as sawdust, pine needles or paper, and allowed to smoke for a predetermined period of time. The carbonaceous atmosphere reacts and affects the glazes and clay, imparting unique effects to the surfaces. For example, some of these effects may be metallic, while others may demonstrate a ‘crackled’ surface. Where the clay body is not glazed, the clay absorbs the smoke; turning black. Once the wares have cooled, they are carefully washed to remove residues of soot and ash.
In a different technique, identified as the Horsehair Process, the burnished, unglazed ware is removed while red hot from the kiln and placed on a special work table. When this ware has cooled to approx 1400 degrees, horsehair is applied to the surface to burn its distinctive patterns into the skin of the ware.
