You could also slow down oxidation by storing pearls (and all jewelry that tends to tarnish) with a small square of anti-tarnish paper (available on...
A lot of risk can be avoided by only using "Friends and Family" for its intended use. It is not meant for purchases and offers no buyer protection. ...
If the pearl itself is not very valuable, and the area of damage is small, what about just painting over the damaged area with a bit of nail polish? ...