Raku is a type of ceramic that originated in Japan about 400 years ago. The differences of raku to other types of ceramic glazing are mostly in the firing, where most other types of firing begin with cold pieces and the firing process can take days. With raku, the pieces are often pre-heated and set into a hot kiln. Depending on the specific glaze used, the finish can become a bright metallic or an exciting blend of colors and cracks.
Building a Kiln
A simple kiln for firing raku does not require a lot of space or expensive equipment. A small oil drum or galvanized metal garbage can, some ceramic fiber, ceramic glue, a shelf for the pots to sit on and a hand-held gas burner or torch are all you need. The ceramic fiber, glue and shelf are all available at any potters' supply shop.
Clean the oil drum thoroughly. Leaving oil in it will only be a fire hazard. With a welding torch or metal saw, cut off the top of the drum, about a third of the way down. Cut a hole in the side, a few inches from the bottom, just large enough to accommodate the tip of the hand-held gas burner. Line the inside of the drum with about a 2- or 3-inch thickness of ceramic fiber, glued to the sides with ceramic glue, leaving the hole at the bottom open. Also, line the lid. Set the ceramic shelf in the bottom. Make sure it sits above the hole for the burner. To use the kiln, light the burner and set it in the hole.
Be certain your burner is an appropriate size for your kiln. A large can will require a larger heat source than a small propane torch.
Take care not to breathe dust from the ceramic fiber.
Rest your heat source torch on a ceramic brick rather than on the edge of the hole in the drum. It is more stable and less likely to deform or set other things on fire.
Raku is a fragile finish and does not stand up well to food use. Any piece of raku pottery should be treated as a decorative object only.
Never fire greenware in a raku kiln. It is a sure way to make your pieces explode. In fact, pre-heating the bisque is recommended.
Do not use cones to determine the maturity of the glaze. It is best to learn to judge by sight whether your pieces are ready to remove from the kiln.