I found this protractor today. It was buried about 3” deep. Green patina and not magnetic 🧲. I’d guess copper. The piece is very thin. I can see the graduation marks in some places. I would like to clean it up to see if there is a manufacturer name, etc in it. What is the best way to clean copper without harming it? I don’t want anything very abrasive. Have been told to soak it in straight lemon juice. I wanted to see if anyone could share a similar experience. Thank you!
