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Copper Carbonate and Copper Oxide. (Note: Copper should not be used in soluble glazes for food and drink containers; in addition to not being safe, it will leach into tea for example, making your tea have a coppery taste.) Not very effective used on it's own. Better to add to or cover with glaze. In an electric kiln it will create a variety of green shades.
In alkaline glazes it will create turquoises. It may achieve red colors in a reduction kiln.