Rusty nail surface. Coloured scanning electron micrograph (SEM) of the corroded surface of a rusty metal nail. Corrosion is the destruction of the metal by chemical reactions. The surface appears uneven due to patches of rust and oxidation and it is weakened from cracking. Rusting is an electrolytic process in which iron reacts with water and oxygen to form an hydrated iron oxide. Rust is more brittle, porous and bulky than iron, and is weaker. Magnification: x600 at 6x6cm size.