I was lucky enough to go to the jewelry school Alchimia in Florence
Italy for two weeks, and they said to use the clear spray for CARS.
I usually like to leave the metal alone, and let it do its own thing
in its new house, but if I want it to stay the same, I use that
spray. I have not had a piece long enough to see the long term
effect. Go to a place that sells car paint, and get the best spray.
Then USE OUTSIDE WITH A MASK. That stuff is powerful.