Raku ware (楽焼, raku-yaki) is a type of Japanese pottery traditionally used in Japanese tea ceremonies, most often in the form of chawan tea bowls. It is traditionally characterised by being hand-shaped rather than thrown. In the traditional Japanese process, the fired raku piece is removed from the hot kiln and is allowed to cool in the open air.
The Western version of raku was developed in the 20th century by studio potters. Typically pots are fired at a high temperature, and after removing pieces from the kiln, the pots are placed in an open-air container filled with combustible material, which is not a traditional Raku practice in Japan. The Western process can give a great variety of colors and surface effects, making it very popular with studio and amateur potters.
Bernard Leach is credited with bringing Raku to the west.
Raku became popular with American potters in the late 1950s with the help of Paul Soldner. Americans kept the general firing process, that is, heating the pottery quickly to high temperatures and cooling it quickly, but continued to form their own unique style of raku.
Raku's has a diverse history of change and adaptation which goes well with its unpredictable results and intense colors. The patterns and color result from the harsh cooling process and the amount of oxygen that is allowed to reach the pottery. Depending on what effect the artist wants, the pottery is either instantly cooled in water, cooled slowly in the open air, or placed in a container filled with combustible material, such as newspaper, covered, and allowed to smoke.
Water can immediately cools the pottery, stopping the chemical reactions of the glaze and fixing the colors. The combustible material results in smoke, which stains the unglazed portions of the pottery black. The amount of oxygen that is allowed during the firing and cooling process affects the resulting color of the glaze and the amount of crackle.
Unlike traditional Japanese raku, which is mainly hand built bowls of modest design, western raku tends to be vibrant in color, and comes in many shapes and sizes. Western raku can be anything from an elegant vase, to an eccentric abstract sculpture.
Western culture has even created a new sub branch of raku called horse hair raku. These pieces are often white with squiggly black lines and smoke-like smudges. These effects are created by placing horse hair, feathers, or even sugar on the pottery as it is removed from the kiln and still extremely hot.
The first Japanese-style kiln in the west was built by Tsuronosuke Matsubayashi at Leach Pottery, St Ives in 1922. Since then Raku has evolved and changes every year with every potter having their own specific Raku technique.
The type and the size of kilns that are used in raku are crucial in the outcome. One aspect that can affect the results is the use of electric versus gas kilns. Electric kilns allow easy temperature control. Gas kilns, which comprise brick or ceramic fibers, can be used in either oxidation or reduction firing and use propane or natural gas. Gas kilns also heat more quickly than electric kilns, but it is more difficult to maintain temperature control.
It is important for a kiln to have a door that is easily opened and closed, because, when the artwork in the kiln has reached the right temperature (over 1000 degrees Celsius), it must be quickly removed and put in a metal or tin container with combustible material, which reduces the pot and leaves certain colors and patterns.
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.
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 smoke scaring and carbon.
Western raku is typically made from a stoneware clay body, bisque fired at 900 °C (1,650 °F) and glost or glaze fired (the final firing) between 800–1,000 °C (1,470–1,830 °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.
Traditionally 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 or 1,800 °F, as opposed to almost 1,260 °C or 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.
Aesthetic considerations include clay color and fired surface texture, as well as the clay's chemical interaction with raku glazes.
In a craft conference in Kyoto in 1979, a heated debate sprang up between Western raku artists Paul Soldner and the youngest in the dynastic raku succession, Kichiemon, (of the fourteenth generation of the "Raku" family of potters) concerning the right to use the title "raku". The Japanese artists maintain that any work by other craftsman should hold their own name, (i.e., Soldner-ware, Hirsh-ware), as that was how "raku" was intended.
Raku in the west has been abstracted and is now a more philosophical approach with the emphasis on the spontaneity of surface pattern creation rather than purely a firing technique. Consequently, this has expanded its application from pots to sculptural ceramics.
The science in the glaze...
In the western style of raku firing you use a reduction chamber. A reduction atmosphere is created by closing the container while something inside is burning, like sawdust. A reduction atmosphere induces a reaction between oxygen and the clay minerals, which affects the color. It also affects the metal elements of the glaze. Reduction reduces the oxygen content after the combustible materials such as the sawdust catch fire and forces the reaction to pull oxygen from the glazes and the clay minerals.
For example, a luster gets its color from deprivation of oxygen. Different reactions cause different lusterous finishes and some will create a metallic effect. Pieces with no glaze have nowhere to get the oxygen from, so they take it from clay minerals. This atmosphere will turn clay black, making a matte color.