Question

How is the property of metal lusture is connected to a photon ?

Answer 1

Metals are lustrous because of the free electrons they have. The free electrons can move freely in the metal causing any light incident on them to get reflected back. This reflection is specular reflection rather than diffused and thus the metal surface appears shiny or lustrous .

As the metal surface (more active metal like iron) comes in contact with environment it form oxides which restrict the mobility of the free electrons. Thus instead of specular reflection we have diffused reflection and the surface of metal appears dull. But in case of noble metals (like gold) the oxides may not form easily, thus they appear lustrous for a long time.