Why do metals appear lustrous?
Light is an electromagnetic wave. A metal has a large cloud of relatively free electrons (electrons that are loosely bound to the metal surface). When a beam of light is incident on a metal surface, it polarizes the electron cloud, i.e. some regions on the metal become relative more "positive" while some regions relatively become more "negative". Thus, this induces a field which makes the electrons to start oscillating. This oscillation generates another electromagnetic wave which opposes the incident radiation, (An ideal metal will completely oppose the incident light radiations), and hence our incident light rays get reflected.