"Rust" is the result of a reaction between iron and oxygen. Copper has no iron in it, so does not rust. It can corrode, though, and yield a bright whitish-blue material.
The only chemical that could make something rust is iron; "rust" refers specifically to the corrosion of iron, so copper cannot rust. However, its corrosion is caused by copper itself being oxidised and forming compounds which are water soluble and also easier to damage.
Copper does not rust like iron, but it can develop a greenish layer called patina when exposed to air and moisture. This patina is primarily composed of copper compounds such as copper carbonate and copper hydroxide, which form a protective layer on the surface of the copper, preventing further corrosion.
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Copper doesn't rust
Copper corrodes, things made of iron rust. Copper can corrode, but it takes longer than it does for iron to rust.
Pennies don't rust. Rust technically speaking is iron oxide and pennies have little to no iron. They do however oxidize, tuning them green from the copper which makes up most of the metal they are made from.
Rust occurs on iron and steel when they oxidize in the presence of moisture and oxygen. Copper does not rust; instead, it forms a patina when it oxidizes, which is a greenish layer that protects the copper from further corrosion.
Plastic pipe does not rust, brass does not rust, copper does not rust. Stainless steel does not rust, lead pipe does not rust.
Most likely some other object has dripped rust onto the copper, which can be removed. Copper does not rust, but it does form a green patina over time.
Oxygen turns copper green.
copper does not rust
Copper does not rust; it develops a greenish film called patina when exposed to air and moisture. The formation of patina can take several years, depending on the environmental conditions.