Bi-Metallic Coins
Apr 1st, 2009 by capitaladmin
Core77 follows up their recent write-up on Production Methods with a quick overview on bi-metallic coins. 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 this method…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.
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. Although these don’t quite meet the standards, coin collectors have a fondness for goofy oddities produced in the manufacturing process and there is quite a number of error collectors out there.
For more on coining, check out Core77’s Production Methods entry.
[photo credits: Flickr user photoshoparama, world coins, wbcc errors image library, wikipedia]
