I recently came up with and attempted an experiment that i thought was pretty cool. I was reviewing chem. one day for an SAT2 that i have later in the year and saw a metal reactivity table. Long story short i saw that it was possible to remove the metal from inside a pennt simply by submerging it in HCl. The zinc is "replaced" by the Hydrogen gas leaving just a copper envelope, lincoln and all still visible. Granted you have to let it sit for a bit and before you submerge it you have to reveal the zinc by cutting into the side of the penny. Damn easy and pretty cool, although im sure many of you have done this already just thought i would share.