Plainsman Clays | COOXB
Copper Oxide Black
Black copper oxide is the more concentrated of the two commonest copper additions, with more copper per gram than the carbonate. It colours glazes and slips.
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Black copper oxide is cupric oxide. It gives a glaze the same greens and turquoises as copper carbonate, and the same reds in reduction. The differences are concentration and grind. It contains more copper per gram, so five parts of it stand in for seven parts of copper carbonate. It is also coarser and does not dissolve as readily, so a glaze with it in should be sieved. Unsieved, the copper shows as specks. Compared with red copper oxide there is no difference in fired colour in an ordinary oxidation firing, because the red converts to this same black oxide on the way up and both finish green. The red is slightly stronger by weight and floats on the glaze water, and the black mixes in without trouble. The shade of green depends on the base glaze, as it does with the carbonate, and like all copper it is a strong flux and evaporates above about cone 8.
- Cupric oxide, a black powder
- More copper per gram than copper carbonate
- Five parts stand in for seven parts of copper carbonate
- Coarser than the carbonate, so sieve any glaze with it in
- Finishes the same green as red copper oxide in oxidation
- A strong flux, and evaporates above about cone 8
