what tools did the mint workers have to polish dies with?
fc
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what tools did the mint workers have to polish dies with?
i am sort of confused here. sandpaper? dentist like tools that had
a rough surface on them or were used to get the sandpaper into
tough areas?
i am rather clueless here. i always just assumed it was a gritty material
like sand paper.
i am sort of confused here. sandpaper? dentist like tools that had
a rough surface on them or were used to get the sandpaper into
tough areas?
i am rather clueless here. i always just assumed it was a gritty material
like sand paper.
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Having some metal working experience though, I'll bet it was an abrasive paste.
<< <i>I don't know the answer.
Having some metal working experience though, I'll bet it was an abrasive paste. >>
i cannot imagine an abrasive paste causing some of the die polish
lines we have seen here unless of course the paste was of such
varying quality of grittiness that it caused all sorts of good and havoc.
imagine using sand one time and tooth paste the next.
good guess though!
<< <i>When ie which time period, I got to think the 1850's the tools were vastly different than the 1890's etc etc. >>
an overview of how they changed would be nice for each period.
but i am thinking 1870-1900ish. the morgan era to be more exact.
you raise an excellent point realone.
<< <i>
<< <i>I don't know the answer.
Having some metal working experience though, I'll bet it was an abrasive paste. >>
i cannot imagine an abrasive paste causing some of the die polish
lines we have seen here unless of course the paste was of such
varying quality of grittiness that it caused all sorts of good and havoc.
imagine using sand one time and tooth paste the next.
good guess though! >>
Modern polishing compounds come in a wide range of grit size. You buy the fineness you want.
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-Paul
Some of them look like they were done with 60 grit emery cloth/paper.
Sort of related article
This would suggest it was done by a tool such as a brush, rather than a polishing from a person.
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I would imagine that I times metal on metal was used to scrape the die (picks for relief areas and chisels for fields). Belt driven sanders and polishers seem quite likely as well for after the heavy debris was removed from the die. And finally good old cloth with some very fine solvent.
<< <i>I don't know the answer.
Having some metal working experience though, I'll bet it was an abrasive paste. >>
Bayard1908 is correct.
The dies were polished by hand lapping them on a cast iron plate with lapping compound.
Lapping compound is an abrasive paste made with a fine abrasive mixed with grease or heavy oil.
I own a machine shop just so you know.
While much of lapping is done with a lapping machine now ( I own a spitfire lap), there are still applications where lapping is done by hand, even now.
Ray
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
For basining dies (adjusting the radius of curvature) and overall removal of minor surface defects (such as clash marks), the mint use a rotating curved zinc disk whose surface was charged with fine abrasive. For localized work they used abrasive on a cotton or silk tipped rod – much like a Q-tip. There were also curved wooden blocks with zinc facing and other tools. There is very little documentation on die maintenance and repair at the US mints – most of the coiner’s records have been lost.
Hope this helps.
RWB
unquote.
thank you everyone for answering. i have a much better idea of what
went on when it comes to polishing the dies.
So it seems pretty clear what the answer is for late nineteenth and early twentieth century. But what about earlier times? For instance, the time before the steam press. Also, what about in today's mint?
Just wondering...Mike
The struck coin would be concave. I have used a PL Morgan for a mirror and focused an image of a sun approximately 25 inches away. That would indicate a radius of curvature of about 50 inches.
The second US Mint used emery (not emery cloth) to polish the dies. I don't know when they used anything different at the second US Mint, but it would have been around the early 1850's and come from the Medal Dept. (George Eckfeldt in charge) when the first sets of "proof" or "master coins" were available to the public after 1853.
<< <i><<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 struck coin would be concave. I have used a PL Morgan for a mirror and focused an image of a sun approximately 25 inches away. That would indicate a radius of curvature of about 50 inches. >>
Right. The disk was concave, which produced a convex die, which produced a concave coin.
TD
<< <i>The first US Mint used salt as an abrasive to polish dies surfaces. >>
Salt was used to polish steel dies?
Why would they not use the same polishing abrasives that silversmiths used to polish their steel tools?
edit - the first US Mint purchased salt, it could have numerous uses such as a flux and/or pickling solution to prevent firescale when annealing, and some could have even been used for the work horses. Salt would have been a poor abrasive compared to what was available at the time.
<< <i>
<< <i>The first US Mint used salt as an abrasive to polish dies surfaces. >>
Salt was used to polish steel dies?
Why would they not use the same polishing abrasives that silversmiths used to polish their steel tools? >>
salt has been known as an abrasive cleaner for a long time.
imagine that today it is recommended as a "green" way to clean.
but i am just as surprised as you. i would have never guessed.
i suppose they simply used what was easily available?
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<< <i>The first US Mint purchased bushels of salt, and it wasn't used for seasoning. >>
"Wasting away again in margaritaville........."
TD
Greek and Roman jewellery By Reynold Alleyne Higgins
the salt process. salt and some organic material, to act as a reducing
agent, are heated in a crucible with the silver-gold alloy. the salt attacks the silver, which is adsorbed by the crucible as silver chloride.
by a combination of this method and cupullation- that is, by heating the ore with lead, salt and barley husks - egyptian metallurgists removed base metals and silver at the same time.
When I told this to John Dannreuther a few years ago, because he has a strong background in chemistry, he immediately understood the significance of salt as a polishing compound. He had originally considered that sand or some other abrasive was used to create the reflective surfaces.
Salt may have been used as a cleaning agent and as an abrasive at the first US Mint. Since there are no technical journals available regarding coinage production, we will never know exactly if there was any other use of salt in such large amounts.
i am getting mixed answers during my search.
If not and given the lack of evidence of salt as a die-polishing material, then I doubt that salt for this purpose was ubiquitous during the early minting days.
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i am getting mixed answers during my search.>>
Interesting! That is exactly half a hundredweight which itself can be 100 or 112 pounds. Generally it is 100 pounds in the US and 112 pounds in Britain. A stone is a popular British unit of weight equal to 14 pounds. 14 does not divide into 100 evenly. The next multiple of 14 is 112 or 8 stones. My present weight is 17 stones 10 pounds and that is how some scales are calibrated over there..
A Philadelphia newspaper (National Gazette) account from June 25, 1793, reported this:
"A correspondent informs us that Mr. Henry Voight, an ingenious clock and watchmaker in this city, and one of the officers of the Mint of the United States, has discovered the method of making steel from iron, which exceeds the generality of any imported cast steel, when manufactured into knives, razors, %c. It is said that Mr. Voight intends communicating this discovery gratis to all the blacksmiths and others interested in iron and steel manufactures...it will then be in the power of every blacksmith to make his own steel".
used for a different purpose then just polishing dies. If we made a list
of all the different things that went on at the first mint and googled
for them + salt.. one might find something interesting that would
require that much salt.
for all we know he used it to de-ice his sidewalks in winter
but i defer to the experts in this case until some hypothesis seems
more then just reasonable to consider as an alternative.
The copper and steel plates would need to be polished to a mirror finish, as any hairlines would show up during printing. Pumice was used as a very coarse abrasive, powdered limestone was finer, and charcoal (lampblack, simply the soot from lamps) would polish to a mirror surface. I would fully expect the same abrasives to be used at the Mint, they were relatively inexpensive back then as they are now.
Try using salt as an abrasive for steel if anyone thinks it was used for polishing, and you will change your mind. Salt would have many uses at the Mint other than polishing, as FC said one of the uses could have been assaying. I had a licenced business/hobby as a silversmith, and trained under a professional silversmith using methods from 200 years ago.
It's from a slightly later period and isn't about abrasives, but it is about salt.
All gold contains silver sufficient to require it to be separated from the gold before the latter can be alloyed with copper for coinage. This operation is termed refining, or "parting." In this process it is necessary to add sufficient silver to make the mass contain, silver, two ounces to one of gold, the principle of the operation being that silver is soluble in nitric acid, while gold is not. After the silver has been dissolved or taken up by the nitric acid, it is recovered and again used in subsequent operations.
When Mr. Peale became melter and refiner, in 1836, the process then in use was that of precipitation by copper, which produced offensive fumes, so much so, indeed, that it was at times impossible for the workmen to remain in the refining-rooms without risk of life. The reduction of silver from nitric acid by precipitation with chloride of sodium, (common salt,) and its recovery by zinc and sulphuric acid, was one of the most important improvements ever introduced into the Mint. Its successful introduction by Mr. Peale attests his genius, enterprise, and high attainments.
Franklin Peale was employed by the Mint from 1833 to 1854 as assistant assayer, melter and refiner and chief coiner.
In 1873, his daughter, Anna Peale, submitted a claim for compensation to the Congress "on account of the benefits derived by the United States from the discoveries, inventions, and improvements in the processes and machinery used in the Mint of the United States."
source: Senate Report No. 454, 42nd Congress, 3rd Session.
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Rick Tomaska interviewed mint workers from the mint circa 1960's and suggested emory cloth as I recall, and said the proof dies were re-pickled with Qtips and acid to create contrast. Makes sense if you look at coins like the 69 proof half. They are frequently blotchy and extremely white even though the die is abraded. Coins like the no initials Walking Lib halfs and the no FG Kennedys are abraded die coins. The LDS 66 Kennedy is abraded until the upper portion of the nose is missing and the eye socket is part of the obverse field.
and it sets us apart from practitioners and consultants. Gregor
The die polisher could direct the amount of pressure applied and pin point areas requiring agressive polishing.
edit: sp and last sentence that I forgot to add.
"Keep your malarkey filter in good operating order" -Walter Breen
Perhaps it was used just to clean planchets prior to minting?