Core77

How they make bi-metallic coins

By Rain Noe - April 1, 2009

in Object Culture

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]

o

Favorite This
Q
5

Comment

Comments

s.

15 years ago

Z

Z

Reply

Put a 2-piece coin on the neck of a bottle.
Place a wooden shaft of diameter roughly matching the inner circle against it.
Knock with a hammer.
Retrieve the inner piece, hammer it back in place upside down or reversed.
Try to get it back into circulation.
!Report as spam
Ful1to

15 years ago

Z

Z

Reply

Uhh! A coin of Colombia! 500 pesos!
!Report as spam
nacho

15 years ago

Z

Z

Reply

the Argentina 1 peso coin have another problem. it's the one in the center of the last three, the one with the sun.
It's says provinGias and must say provinCias. it's a common coin 'cos were made something like forty millions erroneus coins, we're made in 1995 in england.
cheers
!Report as spam
mik

15 years ago

Z

Z

Reply

hhee
and how this are made http://www.krolowiefutbolu.pl/
and http://www.mennica.com.pl/index.php?pt=/1/photo/1014.1,246/znaki_zodiaku.jpg

all made by http://www.mennica.com.pl/
thar are hologram and pictogram types
big up from poland
!Report as spam
Amoxtli

15 years ago

Z

Z

Reply

does anyone can tell me where's the bottom-left coin on the first image?
here's the link to precise what i'm talking about..

http://amx.tumblr.com/post/91855208
!Report as spam