What is the oxide layer on copper commonly referred to as?

The oxide layer on copper is commonly referred to as patina. This green or bluish film forms on the surface of copper when it reacts with oxygen, moisture, and other atmospheric elements over time. The patina is not only a natural protective layer that prevents further corrosion of the underlying metal, but it also gives the copper a distinctive and attractive appearance, particularly in architectural applications.

Patina is composed primarily of copper carbonate and other compounds that develop through the oxidation process. This layer can be desirable in some contexts, such as in architecture and sculpture, because it indicates age and can contribute to the aesthetic value of the copper.

Other terms, such as rust, refer specifically to the corrosion of iron and do not apply to copper. Anodized refers to a process applied to aluminum to create a protective oxide layer and is not relevant to copper. Oxygen itself is a basic element involved in the oxidation process but does not refer to the layer that forms on copper. Thus, patina is the most appropriate term for the oxide layer on copper.