Raku & Saggar Ceramic Firing Processes

The term “Raku” means contentment, enjoyment, and pleasure. Raku describes a process for firing pottery that was originally developed about 500 years ago in Japan. The traditional Japanese Raku process involves a fast firing of the kiln, removing the ware while the glaze is still molten and then a rapid air cooling of the ware. Raku tea bowls were the preferred ware used by the tea masters in the Zen tea ceremony.

Raku became popular in the United States in the 1960’s. American Raku differs from the traditional process in a couple of ways which make a dramatic difference in the appearance. The first difference is that when the hot ware is removed from the kiln it is placed in a reduction chamber, this usually is a trash can filled with leaves or shredded newspaper. The second difference is that instead of air cooling, the ware is quenched in water. Glazes containing metal oxides such as copper carbonate and red iron oxide create metallic lusters on the surface. The pottery is placed in a kiln and fired rapidly to about 1900°F, this takes about an hour. The glowing red pots are removed using tongs and placed in the reduction chamber. The chamber is sealed, creating an oxygen-free atmosphere this changes the surface of the glaze to a metallic luster and the unglazed surface of the clay body turns black as it absorbs carbon from the burning combustibles. After several minutes the pieces are then quenched with water and scrubbed to remove excess ash and carbon build-up. The effects produced are quite variable, unpredictable, and often quite beautiful.

Horsehair Raku pottery is burnished or coated several times with a very fine clay slip called terra sigillata. The terra sigillata is applied when the piece is bone dry but before the bisque firing. The surface is polished after the final coat is applied. After bisque firing, the piece is fired again to a temperature of 1300°F. The piece is removed from the kiln while hot and horsehair is applied to the pot one hair at a time where it burns into the surface. This process must be done within a couple of minutes as the pot will cool very quickly in air. This creates dramatic unpredictable black carbon lines and smoke patterns on the white surface of the clay. The pots are cleaned and waxed to a satin finish.

Saggar fired pottery is coated several times with terra sigillata and prepared in the same manner as the horsehair Raku ware. The ware is then bisque fired and cooled.

Saggars are clay containers that pottery is placed inside of during firing. They were originally used to protect the glaze surface during the firing process. Saggars are infrequently used these days for that purpose. Our saggars are done a little differently and are only used once. Each piece is placed in a paper bag and surrounded with combustibles such as seaweed, straw, fruit peels, sawdust, etc. Also the pieces may be coated with metal oxides, salts and wrapped with wire or steel wool. We have used many of these combinations to create surface effects on pottery. The bag with the pot and combustibles is then sealed and coated with several layers of newspaper dipped in clay slip; this forms the saggar when fired. The slip-coated bags are placed in the kiln while the slip is wet. The kiln is then fired for 2 to 3 hours up to a temperature of about 1700°F. At this point the kiln is shut off and sealed. The pieces are allowed to cool slowly. Once cool the saggars are peeled away and the pots are cleaned and waxed.

These types of firings do not seal the ware completely and it should NOT be used for food or to hold liquids. To clean, just wipe the piece with a soft cloth. Raku ware should not be placed in direct sunlight as the glazes will change over time. Horsehair Raku and saggar fired pieces can occasionally be waxed with Johnson’s paste wax for furniture to refresh the finish.

provided by Donna & Gary Claggett

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