Gas reduction firing uses 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.
Gas Car Kiln, 2008
Robert built this kiln in 2008 after deconstructing his previous kiln built in 1977. He made many improvements over his previous gas kiln. The gas kiln at Robert’s studio is used primarily for bisque firing, as most of his work is fired in one of his wood-fired kilns. However, he does high-fire the gas reduction kiln to touch up pots that may have been under-fired or had unmelted ash deposits from the wood kiln. He also uses the gas car kiln for special glazes such as Copper Red or Carbon Trapped Shino.
Design Elements
The large 6″ wheels on this cart allow it to be rolled in and out of the kiln easily using a metal handle that screws into the frame. Robert’s previous gas car kiln had 4″ wheels and it was necessary to winch the cart in and out.
Gas Car Kiln, 1977-2007
Robert built this kiln in the mid-1970s when his primary business was making Aquariums and Fountains. It was fired weekly for many years.
Firing The Kiln
When Robert built his first wood kiln in 1993, the use of the gas kiln changed and began being used primarily for bisque firings. It was fired over 500 times during its tenure at the pottery. The kiln is shown in 2002 during a reduction glaze firing.
Unloading The Kiln
After the firing, the glazed pots show a variety of reduction effects in the kiln chamber. The darker reds show the areas of the kiln that experienced more “reduction of oxygen” during the firing.
Gas Salt Kiln, 1994-2000
This Gas Fired Salt Kiln served Robert well for six years. It was demolished in March of 200 to make room for his 250 cubic foot Noborigama Wood Kiln.
Alpine, Fast Fire, and Wood Cross Draft Kilns
All of these kilns have been dismantled. The building was taken down and then doubled in size to make room for the Noborigama 250.
Gas Fired Two Chamber Kiln, 1974-1977
This was Robert’s first kiln at his Bristol studio. Constructed entirely of insulating fire brick, it incorporated a two-chamber design. The waste heat from the first chamber was used to bisque fire greenware in the second chamber.
Two Chambered Kiln Under Construction
An article about this design was published in the 1975 December Issue of Ceramic Review, London, England: “Two Chambered Kilns, A New Approach,” by Robert Compton.
Glazed Pots After Firing
View into the glaze chamber filled with planters, after a firing.
Gas reduction firing uses 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 that occurs when oxygen-deprived molecules seek 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 a 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.