Penny cleaning for science fair

Hi, Olivia! You're not alone on this one :-)
This question has been asked enough times that we wrote an FAQ on Cleaning Pennies. I think that you'll find it helpful and interesting. Good luck!

Ted Mooney, P.E. finishing.com Brick, New Jersey

My First Grader is doing a science fair project on cleaning pennies and we have our cleaning products but what we cannot seem to find out is how does the penny seem to get so dirty? Is it because of the copper and people holding it and touching it? Compared to all the other coins it seems the penny gets dirty faster than the rest. If you could help I would appreciate any info you could give.

Hi, Margaret. All metals, except precious metals like gold, tarnish. That means the metal on the surface reacts with the oxygen to form corrosion products (oxides). For example, when iron or steel corrodes, the reaction product is iron oxide (rust), and I'm sure you've seen plenty of that. But copper, which pennies are coated with, tarnishes easier than the nickel that the other coins are made of. Also, copper tarnish is a dark and easily distinguishable brown color whereas the slightly yellowish tarnish on the nickel-based coins is not nearly as obvious.

So, pennies don't get "dirtier" than other coins, their oxidation products or tarnish forms faster and is darker. Good luck.

Ted Mooney, P.E. finishing.com Brick, New Jersey

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