4 stubs in multiple holder	Penny with nick in it

Half pennies after acid	Zn completely dissolved

This is a classic chemistry demonstration/laboratory exercise where post-1982 pennies have been treated with HCl acid. Usually the pennies are nicked like the sample above and treated with acid. This results in the Zn being dissolved away leaving only a thin Cu shell. The bottom left image is of a penny that was sawn in half, mounted on a stub, and then dipped in acid for a couple of minutes. The SEM photographs are based on this stub. The image below is the original SEM photograph with its scale. Based on this scale the Cu covering is ~ 8-9 microns in thickness.