Raku is a pottery technique that has it’s origins in 16th century Japan. The raku technique primarily revolves around it’s firing process although involvement with raku often goes much deeper into its philosophy, roots, and cultural significance. 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.
In order to complete the firing process, the raku pottery must remain in the kiln for approximately 20-30 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. This process is known as “post-firing reduction” as the fire in the can removes the oxygen from the atmosphere inside the can. This causes the glazes to change color and creates the unique patterns.
The raku pottery is capable of withstanding the quick changes in temperature because it is made from a special type of clay that contains extra amounts of grog (bits of fired clay). Traditional pottery clays, on the other hand, would crack from the thermal shock that raku pottery undergoes. With very few exceptions, all raku fired ware is fragile, porous, and generally unsuitable for functional use. Unless such fragile ware is treated post-firing with a non-glaze material, (like Thompson’s water seal in the vases) the pots will sweat water and eventually breakdown. Treat raku as decorative. The occasional use of raku in a functional setting is fine but keep in mind that the glaze is soft and can be easily chipped and end up being ingested. Also, the crackle surfaces can hide bacteria. You may use your pots for food but limit the use to dry food…chips, crackers or a fruit bowl!