I found some old pennies by an old spring this weekend. One is a 1917S wheat penny. The ground they came out of was highly mineralized. On their surfaces, the pennies have black oxidation.
Is there a way to take off this corrosion? I really don't want to use any chemicals, as it may eat at what copper is left.
I have seen programs on TV where old coins found in shipwrecks are cleaned electrolytically by passing a small current through them.
Does anyone know how to do this, or can steer me in the right direction?