Have been doing some metal detecting and wondering if you guys that have metal detectors find many old pennies that are still in decent condition ? The newer ones have been good but I found a 1920 yesterday that looked good and I could read the date before I tried to clean it. It was dark colored, Almost black , Soap and warm water wouldn't do anything so I used vinegar and salt. It must have been oxidized because it came out looking like it had been soaked in acid. Is this frequent with old copper ?