Does it depends on the flatness and pureness of surface. does it change when dust or oxides settle on it.
Relectivity depends is primarily a surface phenomena; it depends upon surface roughness (as it roughens, scattering increases), the purity (surface impurities change the fundamental physical constants), and crystal structure (111 has different properties than 110 crystal orientation for most crystals).
If an oxide has formed, as with aluminum, reflectivity decreases rapidly. This is because aluminum oxide is an insulator, and not a metal, and the natural formation of the oxide results in a roughened surface.
Note that as metals are very strong absorbers of most wavelengths, you will see neither refraction nor transmission unless the metal is very, very thin, typically a few nanometers.