Oxidation firing versus reduction firing
With an electric ceramic kiln you are completely in control of the firing process. But you can’t control the amount of oxygen in the kiln.. And you can do just that with a gas-powered ceramic kiln by reducing the air supply to the kiln. This is called a reduction firing.
Because there is not enough oxygen inside the kiln, the oxygen particles contained in the glaze of your work will be pulled out. And that changes the colour of the glaze. It can also change the colour of the clay. Most stoneware for example contains iron, which will also be affected by the lack of oxygen.
With an electric oven it’s impossible to create reduction firing. There is enough oxygen present in the kiln, and you can’t manipulate the airflow. By definition, this results in oxidation firing.
Although there are potters who try an alternative method: by adding a sealed saggar with burnable materials to an electric kiln, the oxygen in the saggar burns up, which creates a reduction firing. However this is a difficult balancing act, requiring some trial and error to achieve good results.
