How were dies polished/finished in the early days of the US Mint?
MrEureka
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I’m particularly interested in the coins that look PL or SP or PR. 1792-1839. What do we actually know? The more specific and detailed you can be, the better.
Although interesting topics, let’s not go astray into the debate on if early proofs (or specimens or master coins) even exist. For the purpose of this thread, all that matters is what the coins look like and how they came to look that way.
Andy Lustig
Doggedly collecting coins of the Central American Republic.
Visit the Society of US Pattern Collectors at USPatterns.com.
Doggedly collecting coins of the Central American Republic.
Visit the Society of US Pattern Collectors at USPatterns.com.
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Do you have Rogers book "From Nine to Mint?"
Yes. I didn’t remember him covering that ground, but I will look again.
Doggedly collecting coins of the Central American Republic.
Visit the Society of US Pattern Collectors at USPatterns.com.
Oops! I just looked and cannot find what I thought was there either. Within the last year or two in a discussion about polishing dies someone posted an image and explained the process. It may be in one of Roger's book set about the Renaissance of American Coinage.
I suspect that what we "know" about this (at least in terms of the U.S. Mint) is mostly conjectural. I've seen illustrations of the minting process drawn from European sources, but not from the US.
Hopefully I'm wrong.
What is now proved was once only imagined. - William Blake
The image had a rotating vertical disc in a wood frame. Seems to me that a horizontal polishing wheel would be more normal.
For the 1793-1823 period under Chief Engraver Robert Scot, I have gone through all of the Mint records at the federal archives, there is no specific description of polishing dies. One of the few documents that describes engraving is Scot's late 1794 engraving report to Congress, which describes the die engraving process in general terms including forging, turning, filing, annealing, hardening, tempering, and finishing. The dollar or half dollar working dies "may be finished in two days" which would include polishing.
More detail is in a Treasury Department letter June 7, 1799, about 16 supervisor seals that Scot engraved, the size of a quarter and basically the same process as coinage dies: "Turning 16 Ds [dies] 36 [36 dollars, by Eckfeldt], Filing, grinding, polishing & hardening 16" [16 dollars for 16 dies by Scot and Eckfeldt].
Prior to the US Mint, Scot engraved hundreds of copperplates for book illustrations, paper money, etc. The copperplates needed to be polished to a mirror surface, otherwise any scratches or marks would show up in the printing. Scot itemized "polishing and planishing" at 1.5 cents per square inch, about 10 percent of the total cost. Planishing is light hammering of copperplate.
Engravers and silversmiths of the time used powdered limestone "tripoli" for a satin finish, and fine jewelers rouge (iron oxide) for a mirror finish, and also "lampblack" or lamp soot, for a very fine finish. I have used these in silversmithing including polishing steel hammers.
I would expect that Scot used the same polishing compounds for coin dies as he used in copperplate. the "grinding" of the working die to remove the displaced metal lumps from letter punching would take longer than the final polishing. To go from a satin finish to a mirror finish would only take a few minutes on a small steel die.
I don't know if Scot polished all working dies to a mirror finish, but we know that he did at times because there are proof-like coins from that period. Not enough coins survive to determine if all dies started as proof-like, I speculate that most were not fully polished but more of satin finish.
@Nysoto what an incredible post! I am thoroughly amazed that you know this information and are able relate it in a clear and understable manner. For a novice collector looking to absorb information like this that exists in the minds of the many experienced collectors who are members of this forum, your answer to the question is invaluable and much appreciated!
-Paul
Thanks for the nice comments Paul! Researching the life of Chief Engraver Robert Scot has been a hobby of mine for the past ten years.
Great post and responses. Thanks
Nysoto's comments are excellent.
FM2M begins around 1836 with the technological improvements of Franklin Peale and others. Also, I would have pushed the start date back if reliable information had been available. Most of what I found pre-1836 was either hearsay for US Mints, or technology used in Britain, France, Russia and the German states.
However, information from Peale and others are clear than foreign mints used dies that were normally flat and that abrading/polishing was done much as with silverware and printing plates: small soft-wood sticks dipped in abrasives of varying coarseness (often mixed with a small amount of whale oil).
For over a year I've been waiting to catch up with my reading before buying your book. I finally pulled the trigger today. When it comes in I'm down to five books with three in progress.
Idea for new thread...
Where would lapping fit into the process? Grinding, polishing, both, neither?
Doggedly collecting coins of the Central American Republic.
Visit the Society of US Pattern Collectors at USPatterns.com.
I think lapping and grinding would be analogous, but I've been wrong before.
What is now proved was once only imagined. - William Blake
"Lapping" was taken from optical manufacture. An abrasive-charged "lap" was used to grind the surface of a glass objective or mirror to a specific shape and radius of curvature (for spherical figures). A "die lap" was made of tin mounted on a stiff backing and abrasive pressed into the soft metal. The lap had a specific radius which complemented that of the die. A lapping tool could be mounted on a lathe axis and a die pressed against it. However, I have not found any clear discussion for US Mints prior to 1835.
THEN WHERE did I see the image and explanation? I was not dreaming. I'll search the other forums.
...OR --- maybe it came from putting jewelers rouge on the tongues of watch dogs at the early mint?
I checked some time-period references for polishing materials used in engraving. The following excerpt is from my copy of Dobson's Encyclopaedia Volume 6 published in Philadelphia July, 1792 - the engraving article is British origin. "Tripoli" is mentioned several times for polishing, and "lamp-black" is mentioned. "Emery" is also included, this may have been a more coarse abrasive that could have been used for "grinding" - which I believe is the same as lapping. Oil is used at times, certainly whale oil.
I saw the same thing, and I think it may have been here. It's been driving me nuts.
What is now proved was once only imagined. - William Blake
This type of thread allows us to appreciate the advancement of technology in field... very interesting. Cheers, RickO
I’m not sure if it crosses over to die prep but in machining I have always understood grinding to be a first coarse step and lapping to be a more fine cleanup or polishing to eliminate Heavy lines and create a more even mating surface.
For example engine valve seats can be ground with a coarse stone and lapped by hand with a compound using just the valve to eliminate imperfections
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I think the term "lapping" is being used as equivalent to "basining" (perhaps a term used later at the mint)?
In the references to grinding above, to be specific I think grinding means " removing the raised metal around punched letters and figures, and shaping the field to the correct curvature." Do the experts agree?
RE: " I think grinding means " removing the raised metal around punched letters and figures, and shaping the field to the correct curvature."
Part of the difficulty is that we are trying too hard to squeeze specific meaning from an era when "mechanics" were artisans much like silversmiths and other craftsmen. There were no "engineers" as we understand the term, nor were there the specialists we consider normal.
A die for US Mints was slightly curved by lathe cutting, then smoothing with an abrasive disc. Lap and basin are much the same thing by the latter 19th century -- but earlier use might have been different. (Lots of things changed at the Mint after Peale returned from Europe. The report we have is not only missing illustrations, but I suspect he had much more to say that was not written down or is now lost.)
RE:
Rotten stone, also known as tripoli, is fine powdered porous rock used as a polishing abrasive for metalsmithing and in woodworking. It is usually weathered limestone mixed with diatomaceous, amorphous, or crystalline silica (SiO2). It has similar applications to pumice, but it is generally sold as a finer powder and used for a more glossy polish after an initial treatment with coarser pumice powder. Tripoli particles are rounded rather than sharp, making it a milder abrasive.
@RogerB said:
Roger's comments are similar to die grinding/lapping/polishing described in Ephraim Chambers Cyclopædia published from 1728-1738 in London ("Matrix" is a "Dye"):
Additional methods of polishing from Cyclopædia:
I briefly described these in a presentation at the ANS September 2023 Coinage of the Americas Conference