Hi; The best way to clean it is to take a small fold of tin foil large enough to cover both sides of the coin. Form a cup with the coin in the middle of the foil. Make sure the shiny side of the foil is facing toward the coin. Pour some table salt in the center of the cup. place the coin in the cup. Then pour CLEAR Vinegar in the cup enough to cover both sides of the coin. Then pour more salt on top of the coin. Fold the edges of the foil over the top of the coin making sure it makes contact with the coin. Sit back and wait 30 minutes. Then open the foil up. The dirt will peel off when you rinse it. Pat it dry with a "Cloth" TOWEL. NOT a paper towel. They leave lint all over the coin ok. Then just take a wooden tooth pick and "PUSH" the dirt off the coin. DO NOT scratch at the coin dirt ok.
If dirt still remains repeat the above steps making sure to use a clean piece of tin foil ok. This will leave the coin clean and not remove the Patina. That is the best way overall. I've tried all the other ways. This works the best ok. Great find. PEACE:RONB