I've two basses, and and two guitars (my acoustic is a cheap one too), but the metal worn on my Epiphone dot picks up oils and and and chemicals (Hot and Humid hear and Studio room means exposure to cooking vapurs) from the atmosphere really easy. Just looking at the now, the Tuning pegs, bridge, pickup covers, switch bolt, all have a heavy dullness too them, whiles the other 3 guitars looks fine.
Silver doesn't respond well either, but If I put my flutes away, they don't get played so much (Need to get a cabinet made for them)