It's that time of the week again. Here's a two tone candlestick holder with a copper red glaze. The two colors come from the effect of the flames in the kiln. More reduction brings out the red form of the copper glaze. The green is the less reduced area.
Reduction - that's when there's extra, unburnt fuel in the kiln because it's starved for oxygen. And it's starved because I close the flue to a tiny opening so the gases have to hang around in the kiln and can't get out as easily. The fuel tries to find oxygen where it can, which is from the chemicals in the glaze. And that changes the color of many glazes.