I am firing the kiln, everything is more or less going to plan, and here is a photo of the flame caused by reduction firing, earlier this evening.
pretty, isn’t it. reduction firing reduces the amount of oxygen inside the kiln, and the flame is the unburnt gas igniting as it comes up the flue and meets some oxygen. here’s another photo, you can see the orange of the heat inside the kiln around the spyhole bung. I take this out (wearing goggles and fireman’s gloves) to check the cones which tell me how hot the kiln is. it’s orange, not white hot yet, but it gets more yellow – towards white hot – later in the firing. the temperature is about 1180 degrees centigrade at this point.
the point of reduced oxygen? needing oxygen to burn, the flame leaches oxygen out of metallic oxides in the clay and the glaze, reducing ferric oxide to ferrous, and cupric to cuprous – copper becomes red, and iron becomes green, porcelain becomes blue-white, other clays which have iron in them become darker, and generally everything is much more interesting and exciting.