Copper Patina
Definition
Copper forms a dense, adherent patina as its ions react with oxygen and carbonate species, and this patina is often protective. It limits further electron transfer and shields the underlying metal.
Unlike loose rust, the copper patina adheres tightly and slows continued corrosion, which is why copper pipes darken rather than dissolve and why the Statue of Liberty is enshrined in a green protective layer. Copper corrosion is specifically controlled in practice with azole inhibitors that bond to the copper surface. The patina exemplifies a passive film that works because it is dense and adherent.
Related concepts
Part of The Blueprint of Water · 🧱 materials