Copper Carbonate

Source: http://ctmpotterssupplies.co.uk/ceramicmaterialsglossary.html

From CTM:

A strong flux that can cause the solubility of lead in low-sol glazes. The carbonate is weaker but is easier to mix reducing the risk of speckle. 3-7% in the carbonate, or up to 5% in the oxides, will give an apple green colour under both oxidising and neutral conditions; yellow-greens in a potash glaze; blue-greens in a barium glaze; turquoise blue in an alkaline glaze. High lime glazes can create purples; high lime glazes with alumina can create purple sploges. Fired under reduction in an alkali glaze (with addition of tin) it creates a copper red or sang de-boeuf. Some prefer to use the cuprous copper oxide when making reds.