I found this helpful video on YouTube showing how to clean copper and bronze coins. For quite a while I have been looking for better ways to clean the coins I have been finding. I usually clean them with powerful concoctions like vinegar, soda, and other random ingredients from around my house like stain removers and bleach, which most of the time ends up ruining some of the coins.
I have tried the method used in the video and it's much more effective then anything I have ever used before. I found that it not only works on copper and bronze coins, but also with silver coins as well, just use slightly less lemon juice. I hope you find the video as helpful as I did. Video by YouTube user: Digging Norway