We asked Harley J. Spiller to share his favorite facts about money from his newest book, Keep the Change: A Collector’s Tales of Lucky Pennies, Counterfeit C-Notes, and Other Curious Currency.

1. U.S. paper money is not paper. It's cloth. In Ben Franklin’s day, people repaired torn bills with a needle and thread.

2. Serial numbers are not just numbers. They also use letters as part of the alphanumeric code for the 12 Federal Reserve Banks.

3. The ink used for money is high tech—very high tech. It has trackable, magnetic, and birefringent (color changing) properties.

4. The U.S. Mint mutilates coins that are found defective. Culls are run through a “waffling” machine before being sent for recycling, eliminating the need for armed guards.

5. The blue ribbon woven through the new hundred dollar bill contains thousands of micro lenses that make the Liberty Bell appear to dance (and make me feel like I'm looking through someone else’s eyeglasses).

6. A farm in Delaware mulches more than four tons of U.S. cash into compost every day. In previous eras, worn out bills were pierced or burned.

7. The first U.S. cents were 100 percent copper, while today’s pennies are 95 percent zinc with a copper coating measuring only 1/2000th of an inch (as thin as cellophane tape).

8. Pennies buried in a garden will repel slugs, which get electric shocks from touching copper and zinc.

9. U.S. banknotes are made on $7 million Swiss Super Orlof printing presses that exert 60 tons of pressure to force ink into cloth. Prized for their distinctive texture, U.S. banknotes are the finest quality engravings being produced in the world today.

10. Each color has its own physical characteristics. Green was selected for U.S. dollars because it’s the most resistant to fading, flaking, and discoloration.

11. Counterfeit dollars can be too good. Fakes are frequently detected because they are more perfect than authentic money.

12. Sailors used to pass the time by banging on the edge of coins with the heel of a spoon, then cutting the middle out of the thickened rims to make rings for their loved ones.

For more fun facts, lots more, get Keep the Change: A Collector’s Tales of Lucky Pennies, Counterfeit C-Notes, and Other Curious Currency, published by Princeton Architectural Press, now available wherever fine books are sold. Did you know that banks throw away thousands of dollars each year? Buy Keep the Change and find out why.