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Rakuyaki (楽焼) or Raku (楽) is a form of Japanese pottery characterized by low firing temperatures (resulting in a fairly porous clay body), lead glazes, and the removal of pieces from the kiln while still glowing hot. Raku is the traditional pottery form for creating bowls for the Japanese tea ceremony.
In the traditional Japanese process, the pot is removed from the hot kiln and put directly into water or allowed to cool in the open air.
The name Raku was bestowed on 16th century Japanese potter Chojiro by the great Japanese tea master Sen-No-Rikyu after he began making tea bowls to the tea master's specifications. The name as well as the ceramic style has been passed down through the family to the present.
Western Raku Techniques
The use of a reduction chamber was an American innovation pioneered by the American potter Paul Soldner in the 1960s. Typically pieces removed from the hot kiln are placed in masses of combustible material (e.g., straw, sawdust, or newspaper) in order to provide a reducing atmosphere for the glaze, and to color the exposed clay surface with carbon. This last step in the process is unique to the Western form of Raku. Western Raku potters rarely use lead as a glaze ingredient, due to its serious level of toxicity. Glaze recipies which craze (present a cracked appearance) are often used, as the crazing lines take on a dark color from the carbon as well.
Western Raku is typically bisque fired at 900°C (1650°F) and glaze fired (the final firing) between 800-1000°C (1450-1800°F). The process is known for its unpredictability, particularly when reduction is forced, and pots can be returned to the kiln to re-oxidise if firing results do not meet the potter's expectations. The firing times for Rakuware are short, perhaps three hours total, as opposed to up to 16 hours for stoneware firings. This is primarily due to the rapid temperature changes during the process. Raku also eliminates the slow cooling time required in enclosed kilns. As a result of these variations in temperature, clays used for Rakuware must be able to cope with large thermal stresses. The usual way of dealing with this is to incorporate a high percentage of sand or 'grog' (prefired clay that has been finely ground) into the clay before the pot is formed. Most porcelains and white stoneware clay bodies are unsuitable for the Western raku process.
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