Copper Carbonate

Copper Carbonate (CuCO3) is a basic copper salt that supplies copper to glazes in a lighter, finer form than black copper oxide. Where copper oxide is dense and dark, copper carbonate is a soft green powder that mixes evenly through a glaze batch and produces cleaner, more predictable results.

The two materials are interchangeable in most recipes, but copper carbonate is preferred when consistent color development matters. It is also the preferred form for copper red glazes in reduction firing, where its finer particle size and more uniform distribution help produce the deep oxblood reds and peach-blossom pinks that make copper reds so prized.

Copper carbonate behaves identically to copper oxide once fired, since the carbonate releases CO2 during firing and leaves pure copper oxide behind. The practical difference is in handling, mixing, and the slight reduction in color intensity because copper carbonate contains less copper by weight than pure copper oxide.

Typical usage: 1 to 4 percent for greens in oxidation (slightly higher than copper oxide to compensate for lower copper content). 0.5 to 1.5 percent for copper reds in reduction. 4 to 6 percent for saturated metallic surfaces.

Safety note: Like copper oxide, copper carbonate is a leaching concern in acidic food-contact glazes. Keep under 2 percent for food-safe surfaces or restrict to decorative work.