BearBones wrote:I thought that gold was very inert, so why worry about PVC, air, oils or salts? Scratches on a numismatic coin are a different issue. Wouldn't gold hold up well even in a chest at the bottom of the ocean (an extremely corrosive environment)? That's where I keep mine.

Gold is. But that doesn't mean that you should use a Krugerrand for
Chuck-Farthing.
Scratches, fingerprints, etc. all make a coin look less desirable than one without such damage. As I mentioned above, some buy ads for gold Canadian Maple Leaf coins discount the offer if the coin is damaged. If you have a choice between buying two identical (year, gold content, etc.) coins, a beat-up one and a pristine one, which would you pick?
Also, the PVC stuff may "migrate" as well, so a contaminated coin lying next to an uncontaminated coin may transfer the bad stuff.
Finally, careful coin handling is just a good habit to get into. Someday, your 2012 gold American Eagle might have numismatic value to your great-great-great-great grandchildren.