I know this may not be the exact newsgroup to post this question, but it's the closest thing I found.
I have some very expensive copper cookware, and after using on the gas range for some time, the copper of course oxidizes and darkens. I tried to clean it with a mixture of vinegar and salt, and it removed the oxidation, but I left the liquid on one of the items too long and it ruined it: instead of mirror-shiny copper surface, it has milky-looking spots (the vinegar itself started to get a green tinge). How can I fix this? Is it possible to do chemically, or do I have to find somewhere to repolish the item? By the way, the salt I used is not regular but Half Salt (half normal salt and half potassium salt). Thanks for any advice or redirection to other sources of help.