Raku pottery is created with a specific ceramic firing process that uses both fire and smoke to create unique patterns and designs. With raku pottery, the piece is first bisque fired. Then, it is glazed and undergoes a raku firing process. The raku firing process requires a special raku kiln that is fueled by propane and reaches temperatures of about 1800°F (about 982°C).
In order to complete the firing process, the raku pottery must remain in the kiln for approximately 30 minutes. The raku pottery is then removed from the kiln using specially designed raku tongs. While the raku pottery piece is still hot and glowing, it is placed inside a metal can full of combustible materials. The heat emitted from the raku pottery causes these materials to catch on fire.
After the materials inside the metal can catch on fire, a lid is placed over the can and the raku pottery is sealed inside. The raku pottery is capable of withstanding these high temperatures and the fire within the can because it is made from a special type of clay that is capable of withstanding thermal shock. Traditional pottery clays, on the other hand, would crack from the drastic temperature changes raku pottery undergoes.
As the fire consumes the oxygen within the can, it also draws the oxygen out of the raku pottery and its glaze. This process is called post fire reduction. It is the post fire reduction stage that creates the unique look of raku pottery. The resulting patterns and colors are unpredictable, as they are created through the natural process of oxygen removal.
After the raku pottery remains in the sealed metal can for about 15 minutes, it is removed and placed in a can of water. This freezes the patterns that were created during the post fire reduction stage. The amount of time a piece should remain in the cooling water largely depends on the piece and its size. Source: Raku Pottery