This is something my dad found, a kept for a while. Anyone wanna take a shot at what happened to it? The front side is perfectly flat, no indentation, but the back has a huge bulge comming out.
It appears to be an example of an air bubble that got trapped when the clad layers were bonded together during the planchet making process. This is not an uncommon occurrence, but I must admit that I can't recall ever seeing one quite that large.
It depends on the collector - some might pay a few bucks for one of these coins just so they have one for their error collection. But not really - no.
I'm still not convinced on this one. The details are fully struck, so the coin was flat when it was minted. It got bulged later. Could be air in the layers, I guess, but I am wondering what caused it to bulge out after being struck (heat?). I don't think the layers are so elastic that it was bulged as a blank planchet, then squished flat by the dies, then popped back out immediately after minting. My vote is for an altered coin. (Heated, etc., to create the bubble).
That's not quite how it works. The heat that is produced during striking is what causes the gas bubble to form which is why it becomes evident after striking. But you could easily be correct as well.
I have a Ike silver dollar with a bulge like that, except it is one each side and on different parts of the coin. I will be more than happy to send a photo if any one wants one. (i dont have pic taken yet)
Just for the sake of argument, GD, we know that this type of error is known as an "included gas bubble, correct? Also, we know how the three layers of the strips that are used to make sandwich coin planchets are bonded together, right? (high pressure, such as produced by an explosion) It is my opinion that the planchets already have the gas bubble between the clad layers before they are struck by the coin dies. The fact that the gas inside the bubble has no place to go, would be reason enough to explain why the coins are fully struck. If this is wrong, I'd be interested in knowing the correct process behind this type of error.
I agree with your comment that the gas bubble is already there when the planchet is formed. But the pressure at that time is not great enough to produce a bulge in the clad layer. Thus the planchet is flat when the dies strike it and the coin is fully struck. But when the coin is struck - this produces a lot of heat. The heat causes the gas to expand. And during striking some areas of the clad layer are thinned by the metal flow and thickened in other areas. Now combine these two things happening at the same moment - the gas expanding - the heated, softer metal thinning - and the gas now has the abilty to cause a bulge or bubble in the clad layer. Once the gas cools - it contracts again. But by then the metal has already been stretched and the bubble formed. Thus the bubble remains on the surface of the coin. All of this happens in the blink of an eye - less time even. I hope this helps explain the process.
It does indeed. You've painted a very vivid picture in my mind's eye. Thanks for taking a moment to explain exactly what is happening during this process.
This is why I joined this forum. You all are amazing. I may not have many posts but the knowledge I'm picking up from reading the other posts is tremendous. Thanks for sharing your knowledge.
This error type can also be easily faked by applying heat to the coin to create the bubble. Be sure to examine your coin closely and make sure it doesn't look like it's been "cooked".
Thats funny... I found a Kennedy half that has the same thing. The sucker is about a half inch thick on the thickest part of the bubble. Was just going to make a post asking about it when I found this sting. Outstanding definition. Thanks
