Raku ware

A 16th century black Raku-style chawan, used for thick tea (Tokyo National Museum)

Tea bowl with designs of pine boughs and interlocking circles, unknown Raku ware workshop, Kyoto, 18th-19th Century, Freer Gallery of Art

Raku-yaki (楽焼), or Raku ware, is a type of Japanese pottery that is traditionally and primarily used in the Japanese tea ceremony in Japan, most often in the form of tea bowls. It is traditionally characterized by hand-molding of the clay as opposed to turning it on a potter's wheel, resulting in each piece being "one-of-a-kind"; low firing temperatures (resulting in a fairly porous body); lead glazes; and the removal of pieces from the kiln while still glowing hot. In the traditional Japanese firing process, the fired Raku piece is removed from the hot kiln and put directly into water or allowed to cool in the open air. Raku techniques have been adopted and modified by contemporary potters worldwide.

History

The term Raku (literally, "enjoyment" or "ease") for this kind of pottery derives from Jurakudai, the name of a palace in Kyoto built by Toyotomi Hideyoshi (1537–1598), the leading warrior statesman of the time.

In the 16th century, the Japanese tea master Sen Rikyu, who was involved with the construction of the Jurakudai, had a tile-maker named Chōjirō produce hand-moulded tea bowls for use in the wabi style of tea ceremony that was Rikyū's ideal. The resulting tea bowls made by Chōjirō were initially referred to as "ima-yaki" ("contemporary ware"), and were also distinguished as Juraku-yaki, from the red clay that they employed, called Juraku clay. Hideyoshi presented Chōjirō's son, Jokei, with a seal bearing the Chinese character for Raku. Raku then became the name of the family that produced the wares. Both the name and the ceramic style have been passed down through the family (sometimes by adoption) to the present 15th generation (Kichizaemon). The name and the style of ware has become influential in both Japanese culture and literature.

In Japan, there are "branch kilns" (wakigama) in the Raku-ware tradition, founded by Raku family members or potters who apprenticed at the head family's studio. One of the most well-known of these is Ōhi-yaki, or Ōhi ware.

After the publication of a manual in the 18th century, raku ware was also made in numerous workshops in and around Kyoto, by amateur potters and tea practitioners and by professional and amateur potters around Japan.

Raku ware marked an important point in the historical development of Japanese ceramics, as it was the first ware to use a seal mark and the first to focus on close collaboration between potter and patron. Other famous Japanese clay artists of this period include Dōnyū (grandson of Chōjirō, also known as Nonkō; 1574–1656), Hon'ami Kōetsu (1556–1637) and Ogata Kenzan (1663–1743).

Oxidation Reduction

The aluminium container used in raku firing is working as a reduction tube, which is a container with a small hole that allows the carbon dioxide to pass through . By closing the container, a reduction atmosphere is created . A reduction atmosphere needs to be created because of the effects of oxygen on the clay and its color . It also has extraordinary effects on the metals inside the glaze. Reduction is a decrease in oxidation number . Closing the can starves the air of oxygen after the combustible materials such as sawdust catch fire, forcing the reaction to pull oxygen from the glazes and the clay . For example luster duster gets its interesting color from deprivation of oxygen. The reduction agent is a substance which electrons are being taken from by another substance that is being reduced . The reaction uses oxygen from the atmosphere within the reduction tube, and in order to continue, it receives the rest of the oxygen from the glazes . This leaves ions and iridescent luster behind. This creates a metallic effect, pleasing to the eye. Pieces with no glaze have nowhere to get the oxygen from, so they take it from clay. Such an atmosphere will turn clay black, making an unattractive, matte color, with no sheen whatsoever.

Reduction Firing 2

Reduction firing is when the atmosphere inside the kiln, full of combustible material, is heated up tremendously, eventually using up all of the available oxygen in the atmosphere of the kiln. This then forces oxygen from the glaze and clay to be taken out to continue the reaction. Oxygen serves as the limiting reactant in this scenario because the reaction that creates fire needs a constant supply of it to continue, and when the glaze and clay come out hardened, this means that the oxygen was subtracted from the glaze and clay to accommodate for the lack of oxygen in the encompassing atmosphere. This is what causes the Raku piece to take on a black or white appearance, depending on how much oxygen was lost in each specific location of the piece. “Reduction is incomplete combustion of fuel, caused by a shortage of oxygen, which produces carbon monoxide” (Arbuckle, 4). The empty spaces that occur from the reduction of oxygen are filled in by carbon molecules in the atmosphere of the container, making the piece blacker in spots where more oxygen was retracted.

Kilns and firing

The first working Japanese kiln in the west was built by Tsuronosuke Matsubayashi at Leach Pottery, St Ives in 1922.

A vase glazed and fired using the western raku technique, showing the soot, crackle glazing, and random reduction-oxidation typical of this pottery technique.

The type and size of kilns used in raku is crucial in the outcome of the piece being fired. One aspect of raku kilns that can differ and affect the results is the use of electric versus gas kilns. Electric kilns allow easy temperature control. Gas kilns, composed of brick or ceramic fibers, can be used in either oxidation or reduction firing, using propane or natural gas. Gas kilns also heat up much quicker than electric kilns, but it is more difficult to maintain temperature control. There is a note-worthy difference in using an updrift kiln versus a downdrift kiln in Raku. An updrift kiln has shelves that trap heat, creating uneven temperatures throughout the kiln, while a downdrift kiln lures air down a separate stack on the side, allowing a more even temperature throughout and layering the work inside using shelves.

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 taken out quickly using tongs and put in a metal or tin container with combustible material, which reduces the pot, leaving 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. 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 (1,470–1,830 °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. 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 temperaturee (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, white stoneware clay bodies are unsuitable for the western raku process unless some material is added to deal with thermal shock. Porcelain,however is often used but it must be thinly thrown.

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 Rick Hirsh 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.

Design Considerations

Raku is a unique form of pottery making; what makes it so unique is the range of designs that can be created by simply altering certain variables. These variables include wax resist, glazes, temperature, and timing. These four variables ultimately determine the outcome when firing a piece of clay using the raku method of pottery making. Wax resist is a suspension of wax in water which is painted over the bare untainted clay before the raku glaze goes on. This is done so that when the raku glaze is painted on, it does not cover the area where the wax resist was applied, thus creating a design. When in the kiln, the wax melts off and the carbon given off as a result of the oxygen reduction, fills the space area where the wax resist was. This is the result of the combustion reaction. In areas where there is just raku glaze and no wax resist, carbon does not fill the area because the raku glazes contain alumina, which have very high melting points. Raku glazes also contain copper, iron, cobalt, and other metallic compounds, which produce different colors. After the glaze has reached its specific heart the metal in the glaze takes its color. For example, the compound, cobalt, produces a dark blue color, and the compound, copper, produces a green color, but produces a red color when the oxygen in the glaze is completely gone. Any unglazed areas turn black due to the carbon given off from the reduction of oxygen. Next the clay is moved from the kiln to a container which contains combustible organic materials like, leaves, sawdust, or paper. Once the lid of the container is closed the reduction oxidation (redox) process begins. The temperature change from the kiln to the container (usually a trashcan of some sort) is where the combustible material is and where the magic of raku happens. The change in temperature and redox sometimes causes cracking or crazing. Crazing is a consistent cracking in the glaze of a piece, like what is seen on the white crackle glaze. This can sometimes add to the design and other times it may not look great. The timing of when the pieces are taken out of the kiln and placed in water, as part of the process, directly affect the shades of each color. Introducing the water to the raku at the right time is incredibly important, if the raku does not cool enough before it goes in the water as a cooling method, the Raku can crack, break, or even explode! Raku is a fun exciting and unpredictable method of pottery making, it takes time, practice and an understanding of it chemistry to master this ancient Japanese skill.

In literature

• Raku tea bowls play an important part in Rituals, a 1983 novel by the Dutch author, Cees Nooteboom.

Raku Glaze Color

The potter glazes the piece with one or several different types of glaze. The glaze is a mixture of metal and oxygen. The glaze is responsible for the metallic glow that is visible on the pottery after the combustion reaction occurs in the trashcan (Mitchell). This is because when the combustion reaction occurs, oxygen is a reactant in the chemical reaction. When all the oxygen from the trashcan is used, the combustion reaction strips the oxygen from the raku glaze, therefore leaving behind the metallic glow (Mitchell). “For example, cobalt oxide (Co304) is processed in three grades, 71.5%, 72.5% (ceramic grade) and 73.5%. The percentage represents the cobalt contained in the oxide. Each grade can affect the intensity of the blue that will be generated in a glaze. In addition, the quantity of trace elements in a metallic coloring oxide can influence its effect on the glaze color” (Zamek). The amount of oxygen that is present in the trashcan is also what makes the different colors, because if the lid of the kiln used in the second firing process was not correctly in place, then there would be more oxygen present, therefore continuing the firing process longer, turning the colors on the pottery to “hues of ugly green” (Mitchell). On the other hand, if the trashcan cover was tightly in place, the combustion reaction would be shorter because the oxygen supply would run out, therefore the colors would be more black and shiny (Mitchell). The results of the pottery depend on the content of the raku glaze and the amount of oxygen present during the combustion reaction. Different glazes also effect the changing of the colors, making copper the most interesting, and on a certain glaze called white crackle, the glaze actually lets carbon in, making the pottery crackle.

See also

• Chawan
• Horse hair raku

References

• Pitelka, Morgan. Handmade Culture: Raku Potters, Patrons, and Tea Practitioners in Japan. University of Hawaii Press, 2005. ISBN 0-8248-2970-0.
• Hamer, Frank and Janet. The Potter's Dictionary of Materials and Techniques. A & C Black Publishers, Limited, London, England, Third Edition 1991. ISBN 0-8122-3112-0.
• Peterson, Susan. The Craft and Art of Clay. The Overlook Press, Woodstock, NY, Second Edition 1996. ISBN 0-87951-634-8.
• Watkins, James C. Alternative Kilns & Firing Techniques: Raku * Saggar * Pit * Barrel, Lark Ceramics Publications, 2007. ISBN 9781579904555, ISBN 1579904556.
• Branfman, Steven. "Raku FAQs." Ceramics Today. Ceramics Today, Sept. 2002. Web. 6 May 2010.
• Herb, Bill. "What Is Raku." Dimensional Design. Bill Herb A.k.a Dimensional Design, Jan. 2000. Web. 6 May 2010.
• Knapp, Brian J. Oxidation and Reduction. Port Melbourne, Vic.: Heinemann Library, 1998. Print.
• Birks, Tony. The New Potter's Companion. Englewood Cliffs, N.J.: Prentice Hall, 1982. Print.
• Mitchell, John. Personal Interview. 30 Apr. 2010.
• Rhodes, Daniel. “Special Glazes and Surface Effects.” Clay and Glazes for the Potter. Revised ed.

Randor: Chilton Book Company, 1973. 318. Print.

• Zamek, Jeff. "» Glazes: Materials, Mixing, Testing, Firing." » Ceramic Arts Daily –

Featured Tip of the Day. Ceramic Publications Company, 5 Nov. 2009. Web. 26 May 2010. <http://ceramicartsdaily.org/ceramic-glaze-recipes/glaze-chemistry-ceramic-glaze-recipes-2/glazes-materials-mixing-testing-firing/?floater=99>.

• Tim, Andrews"Raku:a review of contemporary work".A.C.Black,London.1994

External links

• Raku museum Kyoto
• e-yakimono.net
• Raku Kiln Building
• Just Raku Newsletter
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