Raku -American Style
The origins of Raku began with the Tea Ceremony in Zen Buddhism in Japan.In the 1960s Hal Riegger, Paul Soldner are some of several teachers who introduced a fast firing process where pieces are removed from the kiln when they reach about 1850 degrees F. and placed into a combustion chamber to reduce the clay boy and glazes with smoke.
A raku kiln can be made using fire bricks or ceramic Fiber and Hardware Fabric. Fiber is the best for insulating a chamber to fire quickly. The fiber can be attached with kanthal wire tied through a button and through the mesh The fiber should be sealed is a coating of ITC sealant, Rigidizer or a solution of Sodium Silicate to prevent the fiber from becoming airborne. It is a known to cause cancer. Precautions should be used to avoid skin contact and inhalation of the fibers.Burners attached to propane tanks should have a regulator to control the pressure.
The photos show preparation of the process used for the following slabs. Latex is applied over a drawing, sprayed with a dry matt raku glaze. The latex is peeled away, a raku luster line is drawn. The pieces are fired upright in the kiln. Because I use matt glazes, a pyrometer is used to determine the temperature. Otherwise, raku can be fired by eye. The luster and shiny glazes bubble up like pancakes before flipping over. Then they flux and become wet-looking. They are removed at 1850 degrees F or ^06. Then they are placed on the ground on straw and covered with a large basin or put in a trash can or individual metal buckets with lids with a combustible material like newspaper. After they are cooled, clean them up removing the soot.. Here are some examples of Raku kilns I have built over the past 5 decades. Wood fired kiln (c.1976) was made of leftover bricks with a fire box and a brick beehive structure to support the barrel(, fired with split scrap 2 x 4 from a truss company, and would fired so fast at the end of the day of firing, batches took less than 5 minutes to melt the glazes.
Other kilns used fiber and mesh, a sawed-off oil drum or steel flashing. I use these kilns for raku, saggar firing , obvara or foil saggars. Fiber is sprayed with Rigidizer or ITC to keep the fibers stable. Always wear protection when working with fiber-respirator, gloves and goggles. The photo with three propane tanks shows three tanks plumbed for 2 burners to avoid freezing tanks. I now use 2 tanks plumbed for each burner for the same reason..I fire with the regulator set at 4.5 to 5 pounds psi.