CuO (Cupric Oxide)

Notas

Cupric oxide (CuO), known mineralogically as tenorite, is an inorganic black solid that serves as a primary source for copper additions in ceramic glazes. It functions as a potent flux, where even minor additions—approximately 2%—significantly decrease the viscosity and improve the melt fluidity of the glass. In terms of thermal properties, incorporating copper into a glaze formulation typically lowers the overall coefficient of thermal expansion, potentially mitigating crazing issues in base glazes. When used in oxidizing environments, CuO remains stable and promotes the development of vibrant green hues, with firing schedules featuring rapid heating and minimal soaking often yielding superior color clarity. Conversely, in reduction atmospheres, the oxide is converted into cuprous oxide (Cu2O), which is capable of producing deep red or 'sang de boeuf' effects. Intermediate reduction or specific lime-heavy chemistry can result in purple tones caused by the simultaneous presence of both oxidation states. Beyond its role as a colorant, CuO is utilized to create decorative blotching and specking when combined with titanium, or when introduced as pure metallic filings. It is also employed as a component in complex pigment mixtures, such as the synthesis of black stains with manganese, cobalt, or nickel. Potters must exercise caution regarding chemical stability; the addition of copper can significantly increase the leachability of lead in glaze systems, necessitating rigorous safety testing to ensure the finished ware is fit for purpose.