Yesterday I mowed down some overgrown areas and exposed zones we have not detected before. I made one pass over a small area maybe 5 feet across and came up with an Indian Head penny buried about 5 inches down all bound up in roots and growth. It's pretty crud covered but in the clear patches you can see the profile and shield on the back. The date is covered and I want to clean it off the see. Ran it under running water and soft brushed away the loose soil. Right now it's soaking in olive oil. It this the best method to remove the crud?