A term used in relation to pottery technology, describing certain firing conditions involving a gaseous atmosphere in which an oxidation reaction (the oxidation of solids) occurs. If a kiln is being fired with good, dry fuel and with plenty of draft, the carbon in the fuel is converted into carbon dioxide, and there is oxygen in the atmosphere. This is the oxidizing atmosphere which causes pottery to be fired to a red or orange color whether it has a slip or not. The opposite phenomenon, a reducing atmosphere, produces black pottery. Much pottery, however, varies in color over its surface caused by changing conditions during the firing process.