Exploding Beaver

spot welder? some sort of acid?

I'd say the Queen doesn't look that good either.

Amazing what some people with too much time will do to a coin.

I can replicate this coin in about 20 seconds with a spot welder. Note that there are two blackened contact points on this coin. If you look at the obverse, that is not a pattern of rust spall, my guess is that the copper plating was starting to melt, underneath the thicker nickel plating....

I suspect Ugly can chime in here, he loves this stuff. I bet he could even tell you the make and model of the welder, and what day of the week the error was made!

The two "blackened" points are not really black at all but they are a nice shade of rust red- that is the normal color of iron oxide. The effigy side shows rust concretions that were transferred either from another coin or an unknown iron object. The discoloration on the coin is from rust staining that could easily be removed with a dip in CLR household cleaner. There is nothing in the discoloration that would indicate an extreme heating event such as a welder.

You can do all kinds of things to coins, without discolouring them, it all depends how hot you run it. I have had lots of success with TIG welding coins. When I can sneak into the machine shop at work, my favorite prank is welding high carbon mason nails to 25-cent coins and Loon dollars and hammering them into soft asphalt in parking lots.

The only thing is you can't really mess around with the zinc-cored 1-cent coins, since zinc has a low melting point (about 420 C) relative to the steel cored coins, and plating metals (Ni and Cu).

A quick search online also shows some examples, like this cool Australian coin:



Here is an American 11-cent piece (note there is no discolouration):




Check out this welding art (that you can sit on). No discolouration there (clad coinage):

http://interior-create.blogspot.ca/...ogether.html

I do a lot of metal detecting and find plenty of coins in similar condition. Any of the newer plated steel coins that have been buried for a short while usually have extensive damage. I have found cents and nickels that were barely recognizable as coins. In fact, It sometimes takes a careful study with the loupe to determine that it's really a coin. They just don't make 'em like they used to.... sigh..

I have to admit--the title of this thread made me laugh on several occasions.
Whatever the specific cause to this coin, I have seen the same effect on plated ferrous objects near saltwater. Once the plating is breached, rust displaces the original volume of metal, which breaks out like a blister. Before long, there is catastrophic failure of the metal, which is why ships have a sacrificial anode attached to the hull.