Were you one of the kids who always got teased because you never seemed to have any nifty silver pennies
in your pockets?
Well, have I got good news for you! Not only am I going to show you (yes, you!) how to make your very own silver pennies, when you're done reading this write up you'll have the power to create even golden pennies.
Unfortunately, however, I can't take credit for the following procedure. It is described in detail at chapter 17 of Daniel C. Harris's wonderful text, Quantitative Chemical Analysis, 5th ed.
1: Find a bright and shiny penny. If no shiny pennies are available, try letting a dirty one soak in some cola for a little while
2: Add around a teaspoon full of granular zinc to 5 wt % NaOH (5-10 mm deep) in a 50 mL glass beaker. Heat to boiling.
3: Using tweezers, carefully place the penny into the beaker.
After several minutes, with continued heating and a little swirling, you'll have a brand new silver penny!
Make sure to remove the penny with your tweezers and to rinse with cool water before handling.
When you get bored of your new silver friend, heating the penny on a hot plate (or a trusty frying pan) on a medium setting will cause the coin to shift from silver to gold.
But how does all of this work?
When you mix zinc with a strong base, Zn and OH- react to form zinc hydroxide
Zn(s) + 2OH- + 2H2O <--> Zn(OH-2)4 + H2(g)
The second step is zinc oxide reacting with the penny's surface to create a deposit of a zinc-brass alloy, the observed silver color.
When the penny is heated, zinc diffuses into the penny, creating an alternate, gold colored alloy.
Note: I haven't yet performed this procedure, so there's no way for me to say how long your pennies will retain their color.