It is a non-corrosive oxide, probably. I would take a soft cloth and buff it. Personally I like the deeper effect of the oxide in crevices and the rest buffed as highlight.

There are jewelers here who can answer it better. If I wanted the whole thing polished as it was when new, I would use an ultrasonic cleaner.

But I am sure that there is a gentle liquid that can be used. Another person will probably post an inexpensive, simpler method here.

Good to meet you! What kind of things do you make?

VRock

The rust is called tarnish and one easy way to remove it from the silver and maybe the copper is to use aluminium, hot water and Calgon bath water softener with a dash of salt. Place your pin on the foil in a glass bowl, add the softener and salt and pour on the hot water. The silver must touch the foil. It is actually a form of electrostripping. If the silver looks white when you remove it, buff on your jeans or simular matterial.If this seems too complex, any of the silver polishes from the drugstore or supermarket will work.marilyn