what is the best metal polish for nickel silver bolsters ( not blades) - i know there are lots on the market - i want one that does not scratch or discolor - used to have a cheap rotary tool with buffing wheels , but don't have it anymore - anyone use polish to clean up old discolored bolsters? and if so , what kind is best - just got a few older knives, never used, blades are fine , but bolsters are pretty discolored and have some spots/some kind of crap on them and would like to clean them up. - thanks