A good inexpensive and effective copper cleaner is just a mix of
common table salt and vinegar. Saturate the salt with the vinegar and
either dip your copper into it, or rub it on the copper. Rinse it
well, Then neutralize it with a mix of baking soda and water. I got
the recipe off the interntet. i just typed in the words “copper
cleaner recipe.” and several recipes popped up. There is one that
includes soap flakes, but it leaves a greasy residue which may or may
not be a problem depending on what you plan to do with the copper.
This formula is supposed to retard any further tarnishing, but was
not good for my purposes as I was planning to enamel the copper and
needed a surface clean and free of any foreign matter.