All of my glazes will vary from piece to piece. The Copper Red, however, is far more unpredictable than the others. These two photos illustrate a couple possibilities. Although temperature can effect the color, the kiln atmosphere during the firing is the principal cause of color variation. Kiln atmosphere in a fuel burning kiln - I use propane - is controlled by limiting the amount of
oxygen available. There are a number of ways of accomplishing this, but in my case I use a damper in the chimney, just as you would in a woodstove. Restricting the amount of oxygen causes a "Reduction" atmosphere, and this is what causes the copper to turn red. (Copper in its oxidized state is green.) The lower photo shows the results of just a bit more oxygen than the upper photo. It is not possible to predict the exact results.
