I have this 1926S which has this rough pitted appearance all over. What might have caused this to happen?
This kind of granular surface occurs on many coins of different compositions. I am not a materials scientist, but have had the thought it might have to do with crystallization or some such phenomenon.
Most commonly, I think it would be from being underground or underwater. It could also be a bad cast fake (good cast fakes will not show this effect; not quite as good cast fakes will tend to show raised bubbles or pimples rather than a pitted effect).
At some point, the coin was covered with verdigris (a copper salt) and then it was subsequently harshly cleaned. The copper component of the salt formed came from the coin - thus you have pitting.
Except if it was a cast I'd also expect some mooshiness and lack of details, but even the smallest details are quite sharp. I say environmental damage did it. Perhaps some exposure to a mild acid might do that too?
What if the copper content of the verdigris did not come from the coin, but an outside source? What would he have then?
Thad can speak for himself, but verdigris is a self perpetuating phenomenon. If one coin gets it, it can spread to uninfected coins pretty easily. Once it is on a copper coin, the copper of the coin is subject for destruction.
Nah....this was an awesome roll find. It clearly shows how an uncorroded coin can become corroded by contact with a corroded coin. It took pretty significant force to separate these two, the verdigris was acting like cement! ALWAYS KEEP CORRODED COINS ISOLATED!
So the second coin does not merely have the first coin's corrosion by-products sticking to it, but is now engaged in corrosion on its own. That explains how the reverse can be so bad and the obverse essentially still clean. I naively expected both sides of any coin to go through the same conditions at the same time and look mostly the same. This demonstrates otherwise.
Yes, these were in contact in a roll. It clearly shows what I call "contact verdigris". Verdigris itself can provide feed materials to start the process on an uncorroded coin. That's because EVERY TYPE of verdigris is actually an active chemical process perpetuated by the environment.
It does not take long to corrode copper coins. I have drink holder cups in my car's console and keep loose change in them and I also put my cold drinks on top of them and the condensation from the cold drinks quickly corrodes those pennies. Lots of moisture wrecks coins quick.
This may explain why the seller's picture from the original listing was so bad. The focus was just soft enough to blur the pitting. I would not accuse anyone of intentionally doing this; there are plenty of poor photos and I have also benefited from that myself.
