Bronze and silver tend to oxidize and naturally patina over time.
To prevent your bronze rings from turning skin a blue-green color, paint
the inside of the ring band with clear nail polish.

To delay oxidation, keep your jewelry away from moisture
and when you're not wearing a piece, keep it stored in a clean, dry place
(a plastic bag works!)

To keep your jewelry shiny, use metal polish (W.J. Haggerty 100 All Metal Polish)
and/or a polishing cloth (Sunshine).