7 different methods: https://www.wikihow.com/Clean-Copper
Use copper cleaner.
Bar Keeper's Friend works the best for me. https://amzn.to/2Pb0yT0
Here are several ideas on hometalk. https://www.hometalk.com/search/posts?filter=clean%20copper
Hi Jkm: My favourite, and easiest, thing to use is Barkeepers Friend. You can get it at most grocery stores by the cleaning stuff. It won't scratch and is just as quick as a wink. Use a slightly wet sponge, put some Barkeepers Friend on it and wipe your brass or copper item. Rinse well and dry and Bob's your uncle! As fast as that:) Good luck