What causes these vertical striations, which I seem to notice more on the plain edges of proof coins? Does it occur after the coin gets struck and ejected, or during rimming? Is it caused by the high pressures squeezing the smooth edge against the collar and forcing it to scrape up and down? Thanks in advance!
My guess is it's from the collar during ejection. Proof coins are struck with higher pressure, so they may be harder to eject. Over time, the collar could develop minor defects through abrasion. Just my thoughts
Then where is the evidence of the tearing from the punch and tear characteristic of the blanking process? Why wouldn't the compression of the metal during the upset mill process erase most /all of the the cut and tear remnants? Why does the higher striking pressure during Proof production leave these artifacts, but its not seen with lower pressures used for business strikes (per the observations of the OP)? Wouldn't multiple strikes during proof production force the metal towards the collar and eliminate most/all of the blanking marks that made it past the upset mill and also contribute to collar abrasion/erosion like worn dies?
I've got to go with @Oldhoopster on this one. Using logic, as he has so eloquently done, would certainly negate any marks from the planchet being cut from the blank sheet, at least in my opinion.
The striations visible on the @iPen photo are pretty fine. It still remains probable that any of the coining operations did not completely remove them.
The striations are the evidence. In most cases it does exactly that. But, if and when the blank cutter is getting a little dull and worn itself, it leaves behind more severe, deeper striations than normal, that are not fully smoothed by the process. It's the same kind of thing as severe pre-existing planchet marks not always being obliterated by the strike. That's just it, it doesn't just occur with Proof strikes. And the higher pressure on Proofs makes little to no difference in what happens to the edge of a smooth edge coin. You have to understand that during the strike, once the planchet metal touches the collar, it can't get pushed against the collar any harder or tighter than it already is. Once it touches the collar it stops dead in its tracks. That's because the additional pressure of a Proof strike is being relieved by the metal being forced into the recesses of the die - which is precisely the purpose of the extra pressure to begin with. It is seen on business strikes just as often as it is on Proofs. And not seen on every single one of either type. Also, all the planchets are the same, all cut by the same cutters. So striations are present on all planchets for both Proofs and business strikes. One thing that can make them more readily visible on Proofs is all the extra preparation that goes into Proofs. Just any lines or tiny flaws are more readily visible anywhere, everywhere on Proofs than they are on business strikes, they are more readily visible on the edge as well because of that extra preparation. That's explained above - once the metal touches the collar it stops, it can go no further and no more pressure can be exerted against it because the pressure against the collar is being relieved by the metal moving into the recesses of the die. You also have to understand that the collars used on smooth edge coins are polished smooth so the coins can be easily ejected. But the cutting edge of a blank cutter, its always rough and its sides are always covered with striations even when it's brand new. The very grinding that makes it sharp creates the striations. And those striations are on the edge of every cut planchet. But as I said above, as dullness and wear of the cutter become more severe it leaves behind deeper, more severe striations that are simply not obliterated during the rest of the minting process.
first I think you need a smooth coin edge for it to be apparent. next I think it's got more to do with the way the metal is worked from the beginning well before the blank cutting, upsetmill or the strike or the ejecting. I believe it's more of the "grain" of the metal/alloy itself in some cases. If the edge is lettered, or reeded, It's not going to be seen, but you will notice these kinds of striations on say an early sac dollar, but they are Horizontal as opposed to vertical, copper core, maganese brass cladding, but much less noticable with the edge lettering nowadays. So, in my opinion, like rings on a tree, metals form layers when heated and cooled into the material to then be rolled out into sheets, and I think depending on the direction it's done, determines the "natural lines" of the metal. I see this even on Steel plate, aluminum plate, Stainless, ect. theres these fine lines that aren't from the sheet rolling on the edge of the plate, or the shear, and even if you cut it and sand it and polish it out, the fine lines are still there. I think it's some sort of flow line to the metal processing. However, I'm not a smelter, and never melted metal and poured it and rolled it out to sheet. So, I could be very wrong. Just going by personal observations.
Once the metal fills the squared off edges of the rim during the higher pressure, multiple strike proof process, any defects in the edge of the planchet should start to be compressed. Erosion/abrasion of the collar seems to be a much more likely scenario than residual punch marks that have been through an upset mill and high pressure, multi-strike proof process Sorry, but I'll just have to agree to disagree.
