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A Brief Description of Raku Firing

© Cassandra Truax
May 2, 2009

Raku firing is unpredictable and volatile, but produces exquisitely beautiful results.

Raku firing began in Japan over 350 years ago and is named for the family who initiated such firings. Raku pieces became prized for use in tea ceremonies. Paul Soldner began a revival of Raku in the West in the 1960s.

The Raku Kiln

In Raku, a ceramic piece is quickly heated to approximately 1800 degrees Fahrenheit. A Raku piece will be brought up to temperature in 40 minutes, whereas other forms of
firing will take hours or even days. Raku firings are most often created in a gas or propane kiln. The gas flame is enhanced by an electric blower, which provides more oxygen to
the flame making it burn hotter. This is similar to what is done in a metal forge.

Removing the Piece

After being heated to a red-hot 1,800 degrees, the piece is removed with metal tongs. The Raku artist must wear leather protective gloves and light cotton clothing to protect himself or herself from the intense heat from the kiln. Synthetic materials such as polyester can melt and fuse to the skin, making choice of clothing an important consideration.

The Reduction Atmosphere and Raku Glazes

The piece is then placed in a closed container, such as a metal garbage can, with newspaper, wood shavings, leaves or other combustibles. The combustible material immediately ignites and the container is then closed. By closing the container, a reduction atmosphere is created. Reduction means the fire burns with a lack of oxygen. Pieces with no glaze in such an atmosphere will turn black. The piece is then smoked inside the container for 10 - 30 minutes. During this time, the glaze reacts with various elements in the container, creating flashes of color and a shiny luster. Raku glazes are formulated to perform in a reduction atmosphere. Some Raku glazes contain copper, and produce a striking, metallic finish. Others create a beautiful, crackle finish. The last step is to plunge the Raku piece into a bucket of water. This cools the piece and stops the glaze from chemically reacting any further. The piece is then scrubbed clean and ready to display.

Raku Dangers

Raku is a volatile process, and a piece may crack or blow up at any point. Pieces are generally bisqued before being placed in the Raku kiln. As well, a clay body containing lots of grog is used to help protect against cracking due to thermal shock. Glazes must be completely dry before being fired. Pieces which have uneven walls are prone to cracking due to the extreme temperature changes of Raku. Pieces with small openings, when placed water, may create a forceful jet of hot water and propel out of the water tub. Raku pieces are porous and cannot be used for food. The reason the pieces are porous is because the clay isn't fired hot enough to reach vitrification. Clay which has been vitrified froms crystals, which are like glass, throughout the clay body. These crystals give the clay strength and make it waterproof. Raku produces extrodinary results which cannot be predicted. The mixture of different temperatures and a broad range of chemical elements make Raku a medium for those who can release control of the results.