[Kurt in NJ]

from the old "Gus" mechanic storys on popular mechanics
"You're not supposed to touch them with your fingers," agreed Gus. "But that doesn't stop you from using a piece of cotton or a soft cloth. A trick that I find works well to dip an old handkerchief in alcohol and then in lamp black. The combination makes a swell cleaner and polish. Don't rub the reflectors too hard, just enough to bring back some of the original silver finish. Of course, if they're too far gone, you can have them re-silvered in almost any large city.

rubber gaskets can cause tarnishing of silver too