I have been told that because of oxidation during firing you

Firing an electric kiln in a reduced atmosphere shortens the life of the elements. A reduced atmosphere is created by burning materials in the kiln that uses up oxygen. As long as the charcoal used in firing bronze clay is held in a container such as stainless steel that includes a good lid, your kiln should be okay. The reduced atmosphere will be confined to the inside of the container. Knifemakers use a similar technique. They wrap high-carbon steel knife blades in a high-nickel, stainless steel foil packet. Inside the packet, they place chips of wood, small wads of paper, or cigarette butts. As the kiln heats, the paper or wood burns, using up the oxygen inside the packet. The edges of the foil are folded over two or three times, so only small amounts of oxygen enter the packet. The reduced atmosphere inside the packet prevents the formation of heavy carbon scale on the blades.