Mirror resurfacing

[dopplerjeff5000]

Good point that what is not reflected is absorbed.

I deposit both Al and Ag quite often. I observe Ag thin films to be typically more reflective than Al films at wavelengths longer than 500 nm and less reflective than Al films at shorter wavelengths. Both will react immediately upon exposure to air, but the Al oxide is essentially transparent while the Ag tarnish is not. One can put a layer on either material which will enhance reflectivity an a specified wavelength as well as protect the coating.