Help me understand why one is 64 and one is 66

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Doug, are you suggesting that it would look like this (Figure A)? That the die is pushed down onto a rotating larger wheel?



If Figure A is what you are suggesting, that is completely contradictory to the process described in From Mine to Mint, where the lap wheel spins upright, and the edge (thickness) of the wheel is where the abrasive is applied and the polishing occurs (Figure B). Can you please explain a bit more. I'm still a bit confused.

 

I was just thinking that this thread really turned into something great.
That 1880 S had a silver lining.

 

There are so many excellent examples of 80-S and 81-S coins available in the market in high grade and DPL that you won't regret sending this one back and finding another.

 

Although the use of diamond dust in polishing is very common today, I am not sure when they switched from files or emery dust to diamond. The book on buffalo nickle proofs in 1936 indicated that previous trials that year produced a more satin finish and so due to public pressure then ( 1936) they switched polishing material and technique to produce mirror die finish. I had assumed that the use of the zinc laps with diamond dust started then as it had become a mainstay in the jewelery industry. I still suspect that neither of these 2 Morgans were die polished with laps and diamond dust, but I guess I need to find a Mint budget record to see what polishing materials were expensed as used. Anyone have one for 1900?

 

In my opinion, PCGS and CAC got it right. It has the look to be in a 66 holder.

 

Geek,

I think you did the right thing. Trust your instincts. I was just looking at some coins (Morgan's) this morning. They were in a PCGS holder, CAC stickered and MS65/66. I didn't like them. I agree that these two companies have much more experience than I do, but just because they're in a holder with a green bean doesn't mean I have to agree with them.

 

I would guess these re-polished die marks are similar to what we call striation marks in the granite world. These are basically caused by tooling a piece of stone in the same singular position. This causes parallel lines from the tool that need to be removed each step of the polishing process. If you skip a step too early, the fineness of the next step is not adequate to remove the previous lines and those lines will show up in the final product unless you go back to a course enough grit to remove the lines. So even though the final product may have plenty of polish, the unremoved scratches will remain.

If this is so, I would imagine the re-polished die marks on coins would actually be raised from the surface of the coin as this would be the reflection of a recessed scratch on the die?

 

Doug did it specifically say also business strike dies or was it proof dies the author was referencing. I can undersand proof dies, but the concept of lapping every dies that was repolished with diamond dust is harder. I do recall several books mentioning that repolishing was done with the die mounted. The easily visible lines seen in the coins in original post are much too large for diamond dust, they would have to be partial carat to produce such size. IMO of course.