Raku is a Japanese word for an unusual firing process and the resulting pottery. The pottery is heated in the normal manner until the glaze melts, and then it is immediately removed from the kiln. The red hot pots are cooled rapidly. Sometimes they are cooled in oxidation but usually they are placed in combustable material which catches fire which is then smothered with a metal container. The result is intense smoke and blacking of the clay, and reduction of the glaze. When copper carbonate is present in the glaze, as it is in these wall hangings, it is particularly responsive and can become blue, red, gold and green.