reduction?

Reduction involves any method which pulls the oxygen out of the glaze. Starve the fire of oxygen and it takes it from the chemicals in the glaze. Oxidation firing is of course where the firing does not lack for oxygen so the oxygen remains in the glaze compounds. Copper goes to red when reduced. Iron can go to a lovely green. In an electric firing it is pretty much an oxidation firing. For the most part copper is going to remain green or blue/green and iron will be brown or if you're lucky reddish brown.

In a gas or wood firing you are always going to get some reduction even when it is being done as an oxidation firing (at least I have never seen an absolutely clean burn) - it his a matter of how much and where that makes the glazes look so interesting because it gives you more variation and depth to the look. It is pretty unpredictable however and you can get some exceptionally ugly colors. Oh but when it works it is worth waiting for!

I now primarily do electric cone 6 firings but I feed my need for the fire with pit and raku.

Donna

P.S. even though there is going to be a loss of Oxygen molecules in reduction, the difference between shrinkage in a reduction and an oxidation firing in final shrinkage is not large enough to be noticed in my opinion but now that you bring it up I'm curious. Has anyone out there measured the difference.