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Would someone please explain how dies are polished?
MikeInFL
Posts: 10,188 ✭✭✭✭
I'm curious as to the method used for die polishing. Do any of you mint process experts know how, precisely, this is done? By hand? By tool? Both? What tool is used? Is it a one-step or two-step process? How has this process changed over time?
Any pertinent details would be appreciated & thanks in advance...Mike
Any pertinent details would be appreciated & thanks in advance...Mike
Collector of Large Cents, US Type, and modern pocket change.
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...the coins with the polish lines do appear to be done with a wire wheel of sorts. jmo
roger may know this.
I'm wondering if each press operator had his own ways of cleaning up a die while it was still in the press.
We need an old time press operator on the forum.
Again, just a guess.
President, Racine Numismatic Society 2013-2014; Variety Resource Dimes; See 6/8/12 CDN for my article on Winged Liberty Dimes; Ebay
<< <i>There was a show on TV about the mint a few years ago. They showed a gal, at the mint, using a die grinder with a polishing wheel and polishing compound doing the mirror finish on a proof eagle coin. She stayed away from the satin areas and only did worked on the mirror. >>
The frosted surfaces of a proof die are incuse, so as long as a worker is careful to maintain a level application of the polishing media, only the flat surfaces of the die that represent the fields on a struck coin will be affected. The Mint workers most likely use a pneumatic orbital polisher with a cloth fiber buffing pad that works a liquid microfine silica based polishing compound over the mirrored surfaces. Much in the same way that a painted surface of an automobile is given its final treatment before application of a sealant.
For the geeky numismatists here like me, this is an interesting paper I located on the subject of the troublesome anomaly of bluing in the process of striking proof silver coins. Note the mention of the usage of diamond paste in the die polishing process.
"Everything is on its way to somewhere. Everything." - George Malley, Phenomenon
http://www.americanlegacycoins.com
More importantly, why do you ask?
Leo
The more qualities observed in a coin, the more desirable that coin becomes!
My Jefferson Nickel Collection
They use fine compounds for proof dies. For buss strikes sometimes it looks like they get brutal.
Notice the polish lines on these cents, the one that still has designers initials and the other one where they almost took the initials off. I don't know if it's a tool or brush or emery paper but it's pretty rough.
1. How were dies polished to produce mirror proof coins?
2. How were dies repaired?
2a. How were dies resurfaced to hide repair or as part of repair?
2b. How were local repairs made to dies (without resurfacing)?
Remember that dies were "polished" at different times in the life of the die using different methods for different effects.
A brand new Morgan die was held against a slightly concave zinc disc that rotated. This "basined" the die, giving it a slightly convex shape that helped the center of the coin strike up better. The basining disc used at New Orleans was not concave enough, which is why O-mint dollars look flatter overall and are often poorly struck above the ear.
The basining also gave the new die its Proof-like fields that were imparted to the coins during the strike. Eventually die erosion removed that P-L finish. Apparently San Francisco rebasined its dies in the 1879-1882 period, which is why so many S-mint dollars of this period have great luster.
When a die was in use, it could get dirty with some of the details or lettering filled in and therefore missing on the coins struck from the die. This was unacceptable, and so a press operator could, at his discretion, "polish" the die with an emery stick or a wire brush or whatever he thought worked to remove the dirt. This could cause random die polishing lines.
Occasionally dies clashed together, and received transfer images from the opposing die. Often this was ignored, but if it was severe a press operator could take the die out of the press and over to a work bench where various grinders and polishing wheels were available. This "repolishing" could result in such things as the 1922 "No D" cent or the 1937-D "3-legged" nickel, though the results were usually less severe.
Hope this helps.
TD
Courtesy of CaptHenway
Do a search using "lapping" & "polishing" from 2001 to present. The results will exhaust you.
R.I.P. Bear
<< <i> There’ll be a research article in the future. >>
<< <i>More importantly, why do you ask? >>
Because I've heard a lot of theories, but little definitive, on this topic. That, and it was the topic of discussion on another forum I frequent.
<< <i>I think you are really asking several questions:
1. How were dies polished to produce mirror proof coins?
2. How were dies repaired?
2a. How were dies resurfaced to hide repair or as part of repair?
2b. How were local repairs made to dies (without resurfacing)? >>
Really, I was interested in business struck coins such as the '55 DDO that Rick posted in another thread.
Or a coin like this Walker:
It takes much more space than these boards have to describe how it was done from about 1850-1950. Also, some techniques have changed a lot and others are the same now.
Other than knowing a die shop employee or engraver (for current processes) or digging through hundreds of thousand of unorganized archive documents, no.... Most hobby publications have some elements of accuracy and others that are just guesses.
Usually, I'd post some sort of summary in hopes it would be useful, but this subject is confusing and requires more explanation than can be done here. (There are also aspects that need to be explored more before publishing anything.)
I’m certain the modern private mint folks can help with current methodology.
This has not been published at this point, but the person who purchased the original document (from QDB) several years ago does plan on releasing this in printed form in due time (no exact date has been set).
I have a copy of what Eckfeldt wrote, and Dave Bowers wrote about this discovery (for which he paid $1804 dollars) in an issue of Rare Coin Review about 8-9 years ago (not sure of the exact issue).
Eckfeldt also mentions when the Gobrecht dollars were restruck in 1851, etc. It's a neat insight. Sorry, but I'm not at liberty to discuss the contents.
<< <i>
<< <i>More importantly, why do you ask? >>
Because I've heard a lot of theories, but little definitive, on this topic. That, and it was the topic of discussion on another forum I frequent. >>
I just think any kind of DP is an inferior surface to original surfaces of a coin. While excessive DP can give a coin a most desireable PL appearance, it's not original. Not that I don't care for PL coins, I do think there are other ways coins get PL surfaces. An EDS strike in one of them.
Leo
The more qualities observed in a coin, the more desirable that coin becomes!
My Jefferson Nickel Collection