The first step is to remove the original oxide layer with sodium hydroxide. Then the aluminium object is put at the anode with dilute sulphuric acid as the electrolyte. Oxygen produced at the anode forms a thick and even oxide coating. A dye such as alizarin in the electrolyte adds to the coating to form an attractive finish. Rusting Iron and most of its alloys do not form a protective oxide.
Iron oxide forms a flaky coating that traps water and gives no protection to the metal.
Fe 2 O 3 is rust. Rusting is the opposite of extraction. For iron to rust there must be air and water. Acids, salts and gases such as carbon dioxide or sulphur dioxide speed up rusting. Prevention of Rust A barrier between air and iron can prevent rust.