In English, we say a bad penny always turns up.  Today we use it to refer to a person we’d rather not see but who keeps coming around anyway.  We don’t think of it as referring to a literal bad penny, a counterfeit penny.  Really, how many of us have ever seen a counterfeit penny?  I’ve been collecting coins for most of my life and I haven’t run across one, or even heard of anyone counterfeiting them.  Why bother?  They wouldn’t be worth the effort you put into making them.  If you’re going to counterfeit, go for $20 bills, or even quarters, at least. There was a time when pennies were worth a bit more, and were worth the effort to counterfeit.  In 15th century England.  At this time, the English penny was a silver coin, not copper.  (There were coins called farthings which were smaller than pennies, and these were made of copper.)  The penny was a fairly valuable coin—more valuable than we think of pennies today, anyway....

English £5 coin.  You can't see it in this photo, but it's got ridges around the edge. Most coins minted in the world today are round.  This is how it’s been for most of history.  But if you look at the edges of most coins of most countries today, you might have noticed they’re covered with even ridges.  The ridges don’t seem to add much to the aesthetic appeal of the coins, but they persist on every one of them.  But why are they there? If you’ve noticed the ridges, you might have noticed that in the countries where they’re used, they don’t appear on every coin.  In the United States, the two lowest denominated coins—the penny and the nickel—don’t have ridges.  (The nickel’s five-cent predecessor, the half dime, which was minted until 1883, did have ridges.  The penny never did.)  This is no accident.  The ridges appear on the edges of the larger coins to prevent an ancient problem: shaving. Coins have long been ma...