Serendipity, zippo, lighter,
Performer borrows spectator’s ring or a marked quarter, wraps it in tissue paper for purpose of cleaning it, then hands the spectator a lighter. “When you light the paper, the paper will burn away, and the unique molecular action will cause the ring/coin to be polished and rejuvenated. It will be like new.”
Spectator lights the paper and, as promised, it burns away in a flash. But the ring/coin is nowhere to be found. Finally, the performer pulls the lighter apart and inside the lighter is the borrowed ring.
Note: you may choose to use a borrowed wedding band, men’s or ladies (without a stone) or a marked quarter.