Though the Japanese word Raku simply means pleasure or enjoyment, it has come to represent a special style of pottery. And while this work originated in Japan, and was developed as a special part of the Tea Ceremony, it has certainly evolved over time, and particularly in the way that Western potters create Raku ware or pottery.
One major difference in our approach is that we Western Potters enjoy using a reduction chamber at the end of the actual glaze firing of our work.
Raku glaze fires are truly quick, generally taking about an hour or less. The kiln is opened while the pottery fired within is glowing hot, with the glazes in an early molten stage. There’s a tremendous thermal shock to the work as it’s removed into the cool air outside of the kiln. At this point the atmosphere around any work taken out with tongs is oxygen loaded. But that atmosphere would do nothing to enhance the glazes… copper oxides in such a glaze would become uniformly green, and the clay body of the pot would be white, grey or perhaps beige depending on the mineral content of the clay.
Our own kiln has been created from an oil barrel, welded to a custom-built frame. There’s an extreme and intense loss of heat. The use of a reduction chamber at the end of the raku firing was introduced by the American potter Paul Soldner in the 1960s to compensate for the difference in atmosphere between wood-fired Japanese raku kilns and gas-fired American kilns.
Typically, pieces removed from the hot kiln are placed in masses of combustible material (e.g., straw, sawdust, or newspaper) to provide a reducing atmosphere for the glaze and to stain the exposed body surface with carbon.
Western raku potters rarely use lead as a glaze ingredient, due to its serious level of toxicity, but may use other metals as glaze ingredients. Japanese potters substitute a non-lead frit. Although almost any low-fire glaze can be used, potters often use specially formulated glaze recipes that “crackle” or craze (present a cracked appearance), because the crazing lines take on a dark color from the carbon.
Western raku is typically made from a stoneware clay body, bisque fired at 900 °C (1,650 °F) and glaze fired (the final firing) between 800–1,000 °C (1,472–1,832 °F), which falls into the cone 06 firing temperature range. The process is known for its unpredictability, particularly when reduction is forced, and pieces may crack or even explode due to thermal shock. Pots may be returned to the kiln to re-oxidize if firing results do not meet the potter’s expectations, although each successive firing has a high chance of weakening the overall structural integrity of the pot. Pots that are exposed to thermal shock multiple times can break apart in the kiln, as they are removed from the kiln, or when they are in the reduction chamber.
The glaze firing times for raku ware are short: an hour or two as opposed to up to 16 hours for high-temperature cone 10 stoneware firings. This is due to several factors: raku glazes mature at a much lower temperature (under 980 °C/1,800 °F, as opposed to almost 1,260 °C/2,300 °F for high-fire stoneware); kiln temperatures can be raised rapidly; and the kiln is loaded and unloaded while hot and can be kept hot between firings.
Because temperature changes are rapid during the raku process, clay bodies used for raku ware must be able to cope with significant thermal stress. The usual way to add strength to the clay body and to reduce thermal expansion is to incorporate a high percentage of quartz, grog, or kyanite into the body before the pot is formed. At high additions, quartz can increase the risk of dunting or shivering. Therefore, kyanite is often the preferred material, as it contributes both mechanical strength and, in amounts up to 20%, significantly reduces thermal expansion. Although any clay body can be used, most porcelains and white stoneware clay bodies are unsuitable for the western raku process unless some material is added to deal with thermal shock.
We take pride in our Raku Pottery: it is art, and a beautiful addition to any space. During the summer months, and during our annual November studio sale, we enjoy demonstrating this technique to visitors. It’s a fun way to enjoy pyromania. If you’re interested in visiting us and hoping to see this technique, it’s best to call and arrange this in advance, especially if you’re visiting Vancouver Island and hoping to see some great sights.