CuO Copper Oxide

I am very pleased with this dish. Photographed here I think it really does look like it has come from the sea. The green dapple is caused by copper oxide which is very fickle in the kiln; one is never quite sure how it is going to behave. In my electric kiln it should always go green because of the oxygen in the firing chamber. The fickleness is in how green it will go (it can go black). The colour green varies according to the glaze I use; but the spectrum can be anything from green to bluish to yellowish to soft mottled pinks and even turquoise depending on what it is mixed with.
Copper also jumps from one pot to another in the kiln and worse than that I have known it to appear on a pot where there has been no copper in the kiln whatsoever. For this reason I never used to use copper, but now it is all caution to the wind in this country. The really amazing thing about copper however is that is goes deep red if the kiln is fired in a wood, oil or gas fired kiln and at the top most temperature you stop all the oxygen entering the chamber causing a reduction. A difficult process and last time I did it left me with no eyebrows or eyelashes.
So next time you look at a copper roof or building you will know why it is green, it has oxidized.