One reason I was sad to see the advent of the Euro was that it got rid of Italian Lira coins. I'd only been to Italy once, but I loved that 500 Lira coin because it was bimetallic, like an old NYC subway token.
If you've ever wondered how they make bimetallic coins, here's the process. They start by punching a hole through a coin blank, or planchet. The core will be remelted for another batch, and the remaining part becomes the "ring," or outer, planchet.
Next they take the "core" planchet, which is made from a different metal and sized to fit inside the ring, and they mill a groove all the way around the edge of it.
Why? So that when the press slams shut on the assembled parts, stamping a relief into it, the inside edge of the ring also deforms and spreads into the groove, locking it into place. Now that puppy's not going anywhere, and you've got your purty two-tone coin.
What's neat is that with this process, you can get some cool-looking accidents. Below are photos of some defective coins where the hole in the ring blank was not perfectly centered, resulting in what you see here. I think that aesthetically speaking, I actualy prefer these mistakes to the originals!
For more on coining, check out yesterday's Production Methods entry.
[photo credits: Flickr user photoshoparama, world coins, wbcc errors image library, wikipedia]