I make mixed media jewelry, and I often finish a metal piece with paints, dabbers, gilders paste, etc...
What 'durable' test to do?? I usually try a 'scratch test'. With a wooden tooth pick, with my nails, with a metal piece? but then I ask myself, who is going to scratch his jewelry with a knife!!!
So my question is, how durable (to scratches) a piece of jewelry has to be?