Iron and all metal components with alloys containing iron can rust. Rust is a water-containing iron oxide compound, i.e. a chemical reaction on the surface of the material, which slowly decomposes it. Rust occurs when iron comes into contact with moisture and oxygen. Untreated iron and steel rust the fastest. Stainless steel can also rust, but stainless steels are very robust and highly resistant to corrosion under normal conditions. Depending on the proportion of chromium in the alloy, steels can also be described as stainless. Gold, platinum, silver and copper, i.e. all so-called precious metals, are pure metals or contain only a very small proportion of iron and cannot rust or cannot be detected. Brass and metal alloys without iron content do not rust either. Source: Two hundred and fifty things architects should know, Michael Sorkin