This cleaning pennies technique uses a basic pencil eraser. How do you go about it? Just start rubbing until you can't rub anymore. The black tarnish will slowly be removed revealing a shiny copper penny.
There is a more elaborate way to cleaning pennies with erasers of course. Try hooking an eraser to the end of a drill or Dremel tool. This will certainly cut down on the elbow pain and visits to the orthopedic doctor.
You will certainly be better off using a chemical agent to clean your pennies but in case there are none available........erasers are always an option.