I was stupid. I have an old hand-made copper and brass light fixture that was very badly oxidized. Because of the way the top section is made I can't get to it to buff it, and I didn't want to remove the rivets to take it apart. So, I applied hydrochloric acid to remove the oxidation and THEN remembered my chemistry classes.

The acid dissolved the copper oxide and created copper chloride, which deposited on the brass parts as well as the copper. As a result, both the copper and brass parts are now a nice raw copper. At least, that is my assumption of what happened.

Any ideas of how to remove the copper plating from the brass?

Many thanks!