Sadly, numismatic societies considered cleaned coins to be chemically damaged; so, when you clean pennies, the pennies lose any numismatic value they may have had. So, while cleaning pennies is a fun science experiment, it is not a good financial move.
A fun experiment is to get a jeweler's scale and to weigh the pennies. Copper pennies should weigh over 3 grams. Zinc pennies weigh something like 2.6 grams.
Someone found a 1983D penny that was on a copper blank a few years back. I did a Google search which claimed the penny sold for $15,000.
@yintercept - I really appreciate your comment. I agree that cleaned (aka "chemically damaged") does not add value.
I was probably not as careful as I should have been when helping my kiddos select their 1983 pennies, but I know we did not have a copper blank variation that you referenced above.
Thank you for adding a new dimension to the conversation.