Here's one way to restore dug Lincolns and Indians pennies. After cleaning off the dirt, put a drop of Tabasco Sauce on the penny. After about 5-10 seconds wipe off - shiny as new. There's some sort of chemical reaction that the copper reacts to the pepper sauce. Caution! If you have a penny you believe is very valuable "DON'T" do this - its better left uncleaned.