Use your head when doing this experiment. An ounce of prevention and all that.
File off the edge of a 1982 or later penny. You'll see the silvery zinc underneath. Drop the filed penny into a small glass with hydrochloric acid in it (get some Muriatic acid from the paint store--it's something like 37% HCl). BE CAREFUL with this stuff, it's very caustic.
You'll see the penny bubbling away as the zinc and HCl react. The copper won't react with the HCl, however. Let the penny bubble until it stops (mine took about 90 minutes). Run the water in your sink at full blast and SLOWLY decant the acid out of the glass and into the sink. Use a metal strainer if you can't pour slowly enough to prevent your penny-copper-foils from pouring out. DON'T add water to your acid in the glass. That's bad.
Rinse the penny foils thoroughly and check them out! COOL! The picture seems mundane until you consider that it is of both sides of the same penny.
