It seems to me that a glass mirror with a metal coating on the back
surface tends to reflect better than a strip of aluminum or aluminum
foil.

Telescope mirrors, however, are coated with aluminum or silver on the
front surface and not the back, to avoid refraction within the glass
or other material, and to allow the optical qualities of the interior
of the reflector support, to be much poorer than that of optical
glass.

The question that I have is this. Does the reflective qualities of
mirrors with the silvering surface on the back of the glass in regular
mirrors, have anything to do with the index of refraction of the
transparent material at the surface of the metal?

Would an optical quality, reflective sheet of aluminum immersed in oil
or in some other transparent material reflect better than one exposed
to air?

Or is the entire reason why mirrors have metal coatings on the back
surface to protect the metal from tarnishing?

Did they used to coat polished metal or foil with oil, and then
overlay the oiled foil with glass before they were able to coat
mirrors with metal back in somewhat earlier time periods?

What is the best way to clean dust from a telescope mirror, without
potentially introducing scratches into the aluminum or silvered
surface?