A Science Experiment

I realize this is a strange thing to do. Yesterday I cleaned pennies. It's been on my 'to do' list for quite a while... obviously not a priority. I have Canadian pennies to give to my students as prizes, but they fight over the shinny pennies.
I got 3 ideas from the internet: Coke, ketchup, and vinegar. I left them all for 8 hours. They all worked... but if you ever decide to clean pennies, I recommend Coke. Just because it doesn't have the mess of ketchup, nor the smell of vinegar.
This penny was in the coke, but was partially covered by another penny. Pretty strong stuff...