I have been known to describe glaze chemistry as high temperature magic and nowhere is this more true than with my Evergreen glaze.
All 9 of these tiles were made using the same clay and glazed with the same batch of glaze, dipped in the same way for the same amount of time and fired in the same kiln with the same firing cycle.
As you can see the results are surprisingly different!
It's a crystalline glaze so I expect to see time black and rust coloured crystals in the finished peices, but the amount and location of these sets of crystals vary depending on the thickness of application, the speed of cooling, where the item was in the kiln and what else was nearby. Every now and then a particularly heavy crop of crystals develops entirely hiding the green - for reasons know best to itself. Where the glaze is particularly thin it can yield a matt black, perhaps a thick layer of black crystals, and when even thinner shows up as a clear transparent. The depth of the green colour comes from the copper oxide in the glaze - as does the red where it was positioned close to the gas jet of the kiln and was effectively reduction fired in and oxidised firing cycle. All told it makes for an interesting but rather unruly glaze!