Along with some clad managed to find in some old yards and at the old high school an old horse shoe, a 1966 Canadian penny, a 1917 wheat cent, and a 1962 Roosevelt dime.
As a coin collector I know not to clean coins but with some of my metal detecting coin finds I will clean them for my 'metal detecting' collection. I often clean up old wheat cents with a pencil eraser Pederson. It seems to work quite well on copper.