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In an oxidation firing, ceramic wares are heated to a certain temperature. The heated ceramics draw oxygen from the kiln chamber and from the flue burner ports, spy holes and any other holes or cracks in the kiln. The oxygen combines with carbonaceous materials in the glazes and ceramic body, turning these into ash. Metal pigments in glazes, such as iron, will oxidize, giving the glaze a particular color. Oxidation firings can be done in most kilns, except those which are not designed for it, e.g. a black firing kiln, where sugar is introduced into the kiln which volatilizes and creates carbon, which is trapped in the clay body, creating a black surface. To do an oxidation firing, leave the burner ports and any damper open, so enough air exchange can happen in the kiln. In electric kilns, oxidation is the norm.