Raku is a type of Japanese Pottery that is traditionally used in the Japanese Tea Ceremony, most often in the form of tea bowls. It is traditionally characterised by being hand shaped rather than thrown; fairly porous vessels, which result from low firing temperatures; lead glazes; and the removal of pieces from the kiln while still glowing hot. Raku means “enjoyment”, “comfort” or “ease” and is derived from Jurakudai, the name of a palace, in Kyoto, that was built by Toyotomi Hideyoshi (1537–1598), who was the leading warrior statesman of the time. 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.
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 familiar technique of placing the ware in a container filled with combustible material, introduced by Paul Soldner, is not a traditional Raku practice. Raku techniques have been modified by contemporary potters worldwide. Raku is a unique form of pottery making; what makes it unique is the range of designs that can be created by simply altering certain variables. These variables which include wax resist, glazes, slips, temperature, and timing ultimately determine the outcome when firing a piece of clay.
Kitty uses a combination of Raku techniques, please find them below.
Crackle glazes: is a glaze with a clear base that contain metallic compounds to add color. Metals such as copper, iron, and cobalt; which produce different colors. After the glaze has reached a certain temperature, the metal in the glaze reacts taking on a specific color. For example, cobalt produces dark-blue, and copper produces green but can also produce a red when the oxygen in the glaze is completely gone. Once the lid of the container is closed, the reduction oxidation (redox) process begins. The temperature change from the kiln to the container is where the magic of raku occurs. The change in temperature and in the redox sometimes cause cracking or crazing. Crazing is a consistent cracking in the glaze of a piece, as is seen on the white crackle glaze. This either enhances or detracts from the design. The timing of removal and placement in water directly affects the shades of each color.
Copper glazes: are treated completely different than crackle glazes. While with the crackle glazes you want the piece to go through an oxidation process and to cool so the glaze will crackle while transferring from the kiln to the reduction chamber, the copper glazes should soak up as little oxygen as possible, you want the piece to go from the kiln to the reduction chamber as quickly as possible. This causes the glaze to have as much reduction as possible and can pull out vibrant flashes of color from the glaze and end with either a matte or glossy depending on the type of glaze that you use colorful look.
Wax resist: which is painted over the bare untainted clay, results in the suspension of wax in water before the raku glaze goes on. This is done so that the glaze 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, that results from oxygen reduction, replaces the wax. This is the result of the combustion reaction. Raku glazes contain alumina, which has a very high melting point. Therefore, carbon will not replace the glaze as it does the melted wax. 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, usually a trashcan, which contains combustible organic materials such as leaves, sawdust, or paper. Kitty explains this technique in the video (in Dutch) below.
Horse hair: Horse hair decoration is a process where the piece is left without glaze and brought up to temperature in the kiln and when removed from the kiln it is not placed into the reduction chamber; instead it is placed in the open where horse hair is strategically arranged on the piece. The horsehair will immediately burn and leave thin linear markings on the pottery.
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. Although some do hand build, most western potters use throwing wheels while creating their raku piece. Western culture has even created a new sub branch of raku called horse hair raku.