Corrosion Beyond Iron

Rust is specifically iron corrosion, but other metals corrode through different chemistry. Copper grows a green patina of copper sulfate and carbonate compounds (mainly brochantite) that actually protects the metal underneath — this is why the Statue of Liberty is green.

Aluminum forms an oxide layer within milliseconds of meeting air. That coating is so hard and tight that aluminum does not visibly corrode, even though it is more reactive than iron. Silver tarnish is silver sulfide, formed when silver meets sulfur in the air. Gold barely corrodes at all, which is why ancient gold artifacts still look new.