Reference Library: Raku
:"Though you wipe your hands and brush off the dust and dirt from the vessels, what is the use of all this fuss if the heart is still impure?" Sen-No-Rikyu
'Rakuyaki' (樂焼き) or 'Raku' (樂) 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. In the traditional Japanese firing process, the pot is removed from the hot kiln and put directly into water or allowed to cool in the open air. 'Raku' is considered the traditional method for creating clay bowls for the Japanese tea ceremony. Raku tea bowls are hand-made from earthenware, each with a unique shape and style.
The term raku is derived from the Kanji character meaning "enjoyment" or "ease". For fifteen generations, it has been the title and seal used by a dynasty of potters whose work formed the central tradition of Japanese raku. In the 16th century, the first of these potters, Chojirō (長次郎), came under the patronage of the Japanese tea master Sen-No-Rikyu. In 1598, the ruler Hideyoshi bestowed the name Raku on Chojirō after he began making tea bowls to the great tea master's specifications. Upon the death of Chojirō in 1592, his son Jokei continued the raku tradition. Both the name and the ceramic style have been passed down through the family to the present.
Raku ware marked an important point in the historical development of Japanese ceramics. With the formal recognition of raku potters in the late 16th century, the Japanese artist-potter first emerged from the anonymity of the general craftsman. Other famous Japanese clay artists of this period include Donyu (1574-1656), Hon'ami Kōetsu (1556-1637) and Ogata Kenzan (1663-1743).
Western raku techniques
The use of a reduction chamber at the end of the raku firing was introduced by the American potter Paul Soldner in the 1960s, in order 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) in order to provide a reducing atmosphere for the glaze, and to stain the exposed clay surface with carbon.
Western raku potters rarely use lead as a glaze ingredient, due to its serious level of toxicity. 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 (1650°F) and glaze fired (the final firing) between 800-1000°C (1450-1800°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 1800°F, as opposed to almost 2300°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, clays used for raku ware must be able to cope with significant thermal stress. 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. Although any clay body can be used, most porcelains and white stoneware clay bodies are unsuitable for the Western raku process unless grog is added.
This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Raku".