USA pennies today are copper plated zinc. Try cleaning a penny by immersing them in a solution of 5% acetic acid ⇦ on eBay or Amazon [affil links] (that's vinegar ⇦in bulk on eBay or Amazon [affil links] , pinch of cream of tartar (my Webster's Collegiate Dictionary says it ...
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...
Homemade cleaners give complete control over the ingredients, they cost pennies on the dollars, and often work better than commercial The Ultimate Trick for How to Clean Shower Grout Mold If you notice unsightly dark spots on your shower grout, it's time to start cleaning. The mold in ...