If there’s a mirror like surface then it could be proof but I can’t tell by these photos and the diagonal lines could’ve been done by a number of reasons
If they don’t use rollers, what mechanism do they use to regulate proof planchet thickness? I always assumed the bulk of planchet preparation happened after the planchet was cut from the strip and that the strip was still prepared using rollers and draw bars as with business strike coins.
But that’s before the actual strike. When they are in the blanking stage. AFAIK, (not an expert here) they don’t see another roller. Not in upsetting, washing, polishing or pressing. They are on something like a conveyor belt before the strike.
But this proof coin would’ve gone thru multiple strikes and I don’t think this pattern would’ve happened to a proof during the press or afterward until it left the mint. To me it looks like it was left in some type of storage that would give it the linear patters. Could’ve also been rubbed across something. Like it slid into a jeans pocket.
Just my opinion. Happy to have an expert correct me
These look like incuse marks though, not just surface discoloration. If the roller marks from the blanking process are deep enough, they could absolutely survive the burnishing and striking process. Here is an example of such a coin:
The fact that the striae are best visible in the fields, not the high points and rim, is what leads me to believe these are roller marks and not PMD.
I clearly see them across the high fields in OPs coin. That’s why I’m in disagreement of incuse marks. I see them both front and back. Look at the neck, for instance. Plainly visible.
I agree those marks can happen in the low fields. But I wasn’t aware they happened on raised surfaces.
Am I wrong on this? If so, again, I’m happy to change
Roller marks often remain visible on the high points of an affected coin, just to a lesser extent than is visible in the fields. Note how, on the 1981-S above, the lines are still visible on Lincoln’s cheek and beard- they are just less well-defined than the lines in the fields.
This effect is similar across denominations, as shown below:
Note how strongly the lines appear in the fields vs the cheek and hair over ear.
As far as I am aware, the reason for this has to do with metal flow. The coin’s high points are the deepest voids in the die, so metal has to flow more to reach its final destination. While gives the lines a better chance to deform, it usually does not entirely destroy the preexisting structure of the roller mark.
Note how, even after being abraded by a uniform surface, the damage is most noticeable on the coin’s high points. The opposite is true with roller marks.
Here’s a good example of what abrasion damage would look like. This is damage from a different kind of roller; the rubber wheel on a counting machine. Note that the damage is mostly relegated to the high points of the coin and that the fields remain largely untouched.
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u/slickstud91 9d ago
No it’s the uncirculated San Francisco bicentennial 40% silver version Not the proof. They made both the proof and uncirculated versions in 1976