Reducing atmosphere

A reducing atmosphere is an atmospheric condition in which oxidation is prevented by removal of oxygen and other oxidizing gases or vapours, and which may contain actively reducing gases such as hydrogen, carbon monoxide and gases that would oxidize in the presence of oxygen, such as hydrogen sulfide.

Materials processing

In metal processing, a reducing atmosphere is used in annealing ovens for relaxation of metal stresses without corroding the metal. An inert gas, usually nitrogen, is used, or for more extreme conditions, hydrogen gas.

A reducing atmosphere is also used in order to produce specific effects on ceramic wares being fired. A reduction atmosphere is produced in a fuel fired kiln by reducing the draft and depriving the kiln of oxygen. This reduced level of oxygen causes incomplete combustion of the fuel and raises the level of carbon inside the kiln. At high temperatures the carbon will bond with and remove the oxygen in the metal oxides used as colorants in the glazes. This loss of oxygen results in a change in the color of the glazes because it allows the metals in the glaze to be seen in an unoxidized form. A reduction atmosphere can also affect the color of the clay body. If iron is present in the clay body, as it is in most stoneware, then it will be affected by the reduction atmosphere as well.