Raku is a pottery technique that has its origins in 16th century Japan. It was likely developed by Korean potters under Japanese rule but the exact circumstances of its development and in what context it was discovered is a mystery. The raku technique, like other pottery techniques such as wood firing and pit firing, primarily revolves around its firing process although involvement with raku often goes much deeper into its philosophy, roots, and cultural significance. Traditional raku and our western version of raku are similar in many ways though there are some significant differences.
To briefly describe the raku process it is noted that most all other types of pottery are loaded into a cold kiln where the firing proceeds slowly until the desired temperature is reached. This firing cycle may take anywhere from 8-24 hours or even longer. When the kiln has reached temperature (which is generally determined through the use of pyrometric cones), it is shut off and allowed to cool enough to be able to remove the ware using bare, or lightly gloved hands. The cooling cycle may last from 12-24 hours or longer. The ware is considered finished when it is taken from the kiln. In raku, the pieces may be loaded into a cold kiln but are often preheated and loaded into a hot kiln. The firing proceeds at a rapid pace with the wares reaching temperature in as short a cycle as 15-20 minutes (though raku firings can last up to several hours depending on the individual pieces and their firing requirements). Glaze maturity is judged by the trained eye without the use of cones or measuring devices. When the firing is determined to be completed the wares are immediately removed from the kiln while hot. Since at this point the glaze is molten, tongs or other lifting devices are used.
This is the stage in the process where traditional and contemporary raku differ in technique and treatment. In our western version the wares are now treated to a ‘post firing reduction’ phase. The wares are put into a container with combustible material such as sawdust, or leaves and allowed to smoke for a predetermined length of time. The carbonaceous atmosphere reacts and affects the glazes and clay and imparts unique effects and surfaces to the wares. Some of these effects are metallic and crackled glazes surfaces and black unglazed clay. When the wares have cooled, they are washed with an abrasive cleaner to remove all residue of soot and ash.
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.