PCGS offering $50,000 reward...

Yeah, sometimes they are, but a whole lot of the time they aren't round at all. I've seen lots of streaks, even seen examples where most of an entire side of the coin has turned red, the same red as so called copper spots. Read some of the posts I've made about gold toning, and yeah, it does tone.

As for thinking about the impurities being stretched out during rolling, if ya really wanna get confused, try thinking about the coin in the 3rd dimension - thickness. And then try to imagine how the impurities just happened to end up in the very top layer of the metal so that they are even visible at all when they show up - especially in metal that is .999 or .9999 pure.

And milk spots on silver, they're not always exactly round either. They're kinda sorta round shaped but I've seen tear drop shaped, irregular blob shaped, and round shaped all on the same coin at times, or separately.

The reward is for safely removing milk spots - not for preventing them. And not to be picky but the reward was originally $25,000, not $50,000. And unless they've upped it in recent years, it still is.

 

I agree with your last sentence, but migrate through the metal ? The only time that can happen is when the metal is in molten form - in other words before it even becomes metal in the normal sense of the word. Once it does harden and become metal, any impurities are fixed in place. And the vast majority of any impurities are going to be scattered about throughout the entire thickness of the metal in individual molecules, with maybe a few small clumps of molecules here and there. As the strip is rolled out to planchet thickness, yeah some of those clumps of impurities may become exposed on the surface. But when the finesess is .999 or .9999 - there's going to be very dang few of them ! And the odds of a single clump, let alone several clumps, just happening to end up on the surface by chance - are astronomical because of the fineness. But yeah, it can happen.

And once the rolling is done and the planchets are cut, visualize the planchet as looking this when viewed from the side, with that small dot in the middle being a clump of impurities -

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You have 2 surfaces, top and bottom, and for copper spots or milk spots to become visible, they absolutely have to be right at the surface of either the top or the bottom. So given the odds I mentioned above, you then have to also consider the odds of a clump or clumps of impurities being right on the surface in that entire thickness. Granted if they are on the surface they can have been enlarged by the rolling. But they first have to be there.

Given all of this, you begin to see how unlikely it is for those clumps to be right on the surface, nonetheless, it cannot be denied that it happens for the spots do appear, and way more often than they should !

There's one very obvious possibility, the fineness is not what is claimed in many cases. That said, all tests, and there are tests, seem to indicate that it is what is claimed.

I guess that depends on how you're defining splatters. But the word itself makes me think of something being deposited on the surface of the planchet or coin. But if that were the case, then dipping could and would remove them. But since dipping doesn't remove them, it kind of dictates that they are not splatters being deposited on the surface after planchet or coin formation.

 

I think you're missing my point, but that may be my fault for not making it clear enough. Even if you're correct and atoms can migrate through metal, I somehow doubt that because solids simply cannot move through other solids, but for the sake of argument let's say you are correct. When milk spots and or copper spots form on coins of .999 or .9999 fineness - we're not talking about atoms migrating here. We're talking about entire solid clumps of impurity, roughly the same size as the resulting spots, migrating through another solid. And that just isn't gonna happen as a result of the planceht being heated up. Wherever those clumps of impurities happen to be in the planchet, that's where they are going to stay.

In addition to that, if it was just atoms of impurities somehow migrating to the surface during the planchet being heated, those atoms would then somehow have to manage to migrate further, possibly even sideways, then somehow congregate together and form good sized clumps before you could even see them. You can't see atoms, you can't even see molecules. What I'm getting at is we're talking about clumps of impurities that are at least as large or larger than the period in this sentence. And those aren't going to migrate through another very dense solid just because it gets warm during annealing.

So yeah, I think it can be ruled out.