Copper's natural color changes have nothing to do with rust, but rather are due to a different chemical reaction that creates a layer of patina over the metal. Copper can't rust because it doesn't ...

Over time, blocks of copper will begin to oxidize and change color from their standard copper ... For example, iron oxide-based metals rust after exposure to open air and moisture.

Copper has a beautiful reddish hue, but when exposed to the elements, the metal undergoes a series of chemical reactions that make it turn green. But why does this color transformation occur?