Hello, Tiffany. There could be invisible oils on some pennies and not others, or small variations in the copper purity, etc. The oxide that gives the dark 'aged penny' look could be thicker on some than on others. So I don't think there is a good way of PROVING the pennies are equ...
DIY Swiffer WetJet Solution: Make Your Own Multi-Surface Cleaner for Pennies If you own a Swiffer WetJet Spray Mop, chances are you absolutely love it. But let me guess: You're not 13 Reasons to Keep Borax in the House (and Why It’s Safe!) ...
A lengthy internet search led me to you. You wrote a paper "The Household Chemistry of Cleaning Pennies" but I am unable to read it since I am not a member of the JCE. As far as I can determine, the acids (usually vinegar - acetic acid) break the copper oxide free from the penny...