Raku is a firing process that originated with the Japanese tea ceremony. Ware is quickly brought to a temperature range of approximately 1800 degrees F and is immediately placed in a container of combustable material such as paper, sawdust or straw. After it ignites, the container is sealed to cut off oxygen. The metalic compounds in the glaze create dramatic, unpredictable results in this "reduction" atmosphere. Often the surface becomes "crazed" or develops a crackle pattern . Unglazed areas become blackened from carbon.