Oxide removal on copper using non-acidic methods

Is there a non-acidic, mild chemical or other method to clean oxide on copper surface of small parts? After vacuum metallizing high purity copper on ceramics or plastics, we find various amounts of tarnishing on the surface. This is because the parts are warm when they come out. Cooling inside vacuum is not an option because it takes too long and reduces througout. This tarnishing is strongly associated with moisture level in the air that day.

Well, it's not non-acidic, but the inhibited sulfuric acid (copper sulphate) + hydrogen peroxide mixture is relatively mild and an excellent bright dipping process. I read about an even milder mixture of vinegar ⇦in bulk on eBay or Amazon [affil link] plus drugstore hydrogen peroxide at artmetal.com.

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey

I would assume that some mixture of citric acid ⇦ on eBay or Amazon [affil link] would work ok and safely. My preference would be to backfill the cavity with nitrogen during cooldown. N2 from a liquid N2 dewar is not terribly expensive, is very simple to operate and will drop the temp fairly rapidly as well as provide a non oxidizing atmosphere. It is worth a test.