Red copper is a reduced form of the normal black copper oxide (CuO). In normal oxidizing firings it will transform to the cupric oxide form (CuO) to produce the normal green coloration in glazes and glass. If fired in reduction, it will maintain its Cu2O structure to produce the typical copper red color. See CuO, Cu2O oxides for more information. If red copper oxide is considered as a source of CuO to the final glaze, which in most cases will be true, the conversion factor is 1.12. This reflects the fact that the Cu2O picks up an extra oxygen atom to become 2CuO, weighing 1.12 times more than Cu2O. Source: American Chemet Corp., 708-948-0800 FAX 708-948-0811 Note: Red copper oxide is usually surface coated to prevent oxidation. For this reason, it may be very difficult to get the material to mix with a glaze slurry. If so, you must soak the material in alchohol to wash the surface or add a few drops of detergent to the glaze mix.