Featured Large Cent struck on Defective Planchet

Some where you can plead to the moderators that a thread becomes a "featured thread" I don't remember how to get there. I believe it has to get kinda voted in.
Makes you wonder if the coin sat in a acetone bath for too long, the cold could have helped the fracture.

 

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I would bet that it is a defective alloy. Copper is a malleable metal normally bends. This coin exhibits brittle fracture and that's not normal

I suppose it could be from extreme cold, but I think it would need to be in the liquid nitrogen range. It would be interesting to see the fracture surface.

EDIT. I found some research info that indicates copper maintains its ductiliity at very low temps

 

What is that

 

Qi Knife from 400-250 BC

 

I'm going with isolated impurities or discontinuities in the raw material. But, the only way to be sure would be to submit it to metallurgical examination and that may be destructive or cause more damage.

 

I once dropped an antoninianus on the floor in my office and it broke into many pieces. So yes, stuff happens when you get very old. Happy New Year.

 

Some pics of the break:

 

Chocolate coin.

 

Did a little searching, and contamination of the copper, most notably by bismuth at levels over .003%, can cause brittleness and fracture in rolled copper.

 

If it was crimped back together, then you should see a corresponding impression on the obverse which I do not see. Plus I don’t see how crimping would hold the pieces together. If someone tried to put the pieces back together then they would have used some type of adhesive.

Instead, the impression was likely caused by another impact force which lead to the break.

 

But copper is a very ductile metal. How could it "break" like that without any evidence of significant bending. It has to some sort of alloy problem. @TypeCoin971793 A handheld XRF might give an idea of what else is there besides copper. You might want to try it, if you have access to one. I don't have a lot of confidence in the algorithm in trace elements, but it's worth a shot. An SEM/EDS would tell for certain, but unless you have any buddies at a university analytical lab, that test could be expensive.

 

Perhaps it was improperly heat treated prior to striking so the material was too hard and brittle.

I am actually a metallurgist with over 9 years of failure analysis experience and I am currently the manager of a materials engineering / chemistry lab with access to a SEM/EDS

 

There is a corresponding flat area on the obverse from where the design was crushed. Plus this extra damage follows the curve of the break and is step-wise in manner. Unless something of the exact shape of the impressions hit the coin, the simplest explanation was that someone tried to crimp it back together. Obviously, it was a failed endeavor.

Also, what reliable adhesives were available 150 years ago?

 

We don’t know when it fractured. It could have been 150 years ago or 50 years ago.

The coin appears to be slightly bowed or curved with the obverse side being convex and the reverse side being concave. Can you confirm if the coin is curved or flat? Also, is that a secondary crack through the star at 12:00 on the obverse?

 

What about a deep freeze and then struck with a blunt object? Cold seems more likely to make metal brittle. Otherwise the alloy theory sounds viable to me.

 

Because it appears someone made the attempt for it to be usable in circulation again, I was presuming that the break was contemporary with the circulation.

It is indeed very slighty bowed. I did not notice it until I made the edge pics.

Yes, but the line seen is mostly the imprint of the rim of another coin. There is a tiny, shallow crack on the rim that just enters the field.

Copper is still maleable even in cryogenic temperatures.

 

I think it was a alloy mix problem a vein of a different metal that caused the brittleness. You can see the different color around the break. And the crystalline structure in the break shows it being natural to the metal not done with some tool. Very cool thing. Probably when it broke and couldn’t be spent someone said what do I do with this thing tossed it in a drawer and forgot about it for a hundred years

 

This is definitely an interesting case.

It appears the fracture initiated on the obverse side and propagated towards the reverse side. This lines up with the bending. The bending stresses will put the obverse side in tension and the reverse side in compression. The compressive strength is significantly higher than the tensile strength, so you would expect the fracture to initiate on the observe side. There could be some bending fatigue. I see what might be ratchet marks and beachmarks, but it is hard to tell because the fracture surface is heavily oxidized. Fatigue is a brittle failure that can occur in ductile metals, including copper, due to cyclic stresses. I just don't know how a coin would be used in a way to subject it to such stresses. Maybe the coin was used as some type of wedge, but I would expect a lot more surface damage if that were the case.

The strike at 2:00 on the reverse shows a lot of deformation and ductility without any evidence of cracking, so the material does not appear to be inherently brittle.

Bismuth and lead impurities would result in precipitation of detrimental phases at the grain boundaries leading to brittle intergranular fracture. Again, it is hard to tell from the photos, but it does not seem like an intergranular fracture. You might be able to determine the fracture morphology on the SEM if it’s not completely obscured by the oxide layer.

 

The different color looks like oxidized copper vs smeared un-oxidized copper