Gas reduction firing uses a fuel, such as natural gas or propane. The temperatures of a gas fired reduction kiln may exceed 2300F, when the glazes melt and mature. Because gas is a combustible fuel, the potter can control the ratio of oxygen to gas during the firing.
Depriving the kiln of oxygen creates an atmosphere known as reduction, where carbon monoxide can be produced. By reducing the oxygen during this refractory process, the glaze colors will change and become enhanced. This can only occur in fuel fired kilns.
It is the burning of chemically combined oxygen in the clay and glaze minerals that gives reduction fired pottery its unique characteristics.
The reduction cycle is responsible for a wonderful and unique palette of colors which occur when oxygen deprived molecules seeks the chemically bound oxygen from minerals that are in clay and glazes.
A classic example of a reduction glaze is “Chun Red” also known as “Copper Red.” This glaze dates back to the Sung dynasty in China.
Copper produces a grey, white or green color when fired in an oxygen rich atmosphere. However when fired in a reduced oxygen environment a glaze containing copper can turn a variety of reds ranging in color from peachy pink to bright apple red.
Many glazes are enhanced by reduction firing, but copper red glazes are some of the most dramatic.
Gas Fired Kilns may not produce pottery with the even and consistent results of electric kilns, however reduction firings can yield subtle hues in the color of the clay body, and variations in the glazes, which make each pot unique.