Geochemical analysis of US silver?
shirohniichan
Posts: 4,992 ✭✭✭
I just saw this article this morning:
numismaticnews.net/article/high-tech-coin-research-reveals-metal-source
Is anyone here aware of mass spectral or other geochemical analysis used on US coins to determine the source of their silver content? I'm interested in finding out how many coins minted in San Francisco came from California silver vs. that of Nevada vs. the melting of foreign coin.
Obscurum per obscurius
2
Comments
Interesting article, thanks for posting. Can the analysis be specific enough to distinguish Comstock load silver in a Morgan dollar vs. High Sierra silver in a S mint half dollar?
it's crackers to slip a rozzer the dropsy in snide
Good question,
I'd love it if an analysis could tell us if a coin were minted from silver found in the Inyo Mountains (most likely Cerro Gordo) vs the Comstock. More likely it should be able to distinguish Comstock silver from Mexican or South American silver. The again, silver francs and 5 franc pieces were a "drug on the market" in 1850's California and may have been melted for recoining once they were withdrawn from circulation. Imagine finding an 1858 S half dollar minted with silver from Joachimsthal (modern Jáchymov).
Obscurum per obscurius
It's generally done by trace isotope ratio. I know it to have been more commonly done with gold bars as a means of determining counterfeits.
I think that the refining process would eliminate trace elements and then adding the copper back into the mix could throw a huge monkey into the mix.
bob
Modern refining (circa 1850 forward) obviates useful results. However, dore silver, amalgam, mine bars, and native ore can be used to pinpoint the mining area and sometimes a specific mine.
Roger, thanks. Your answer makes a lot of sense.
it's crackers to slip a rozzer the dropsy in snide
Very interesting, thanks for posting. Seems like they analyzed the isotopes in the lead that was an impurity. (Lead is hard to separate from silver, I doubt that it would be added intentionally.) I agree that intentionally added copper would confuse things. It would be really fun to trace where specific metal bits came from.
Depends on whether they took a silver deposit and refined it down to pure and then re-alloyed it with pure copper to get virgin alloy, an expensive process, or just melted a huge lot of already alloyed metal. tested it while the pot was still molten, and then added a small amount of pure silver or pure copper to adjust the net content to the desired level. If they did that, the trace elements of the deposit remain in the alloy.
Because precious metals do get recycled, a single half dollar made in 1853 could have had trace elements originally made into 100 different coins over several centuries on three or more continents. Or it could have been made from new ore. That's just the way they did it. They did not care about the source of the metal, just the finished product.
Archeologists use trace elements to aid in identifying mining and trade routes, coinage circulation and related subjects. Crystallization is also used to confirm age and certain aspects of environmental conditions.
Actually this technology will become far more advanced in time and the ability to pinpoint sources and alloy will improve. This will prove especially important with ancient coins and even more with ancient tools going back to the early bronze age.
Of course we'll never get to the point we can count the number of '16-D dimes in a 100 Oz bar.
Certainly this would apply to the eastern mints (P,D,C & O). However, the western mints, where the mining was happening would likely have been a raw ore source rather than other coinage. Carson City, Denver and San Francisco were all in mining areas and the source for the cons was likely nearby native ores. Those had to be refined. Perhaps not so in the other mints as they were not near any real silver/gold source.
So, likely is a mixture of both, 'eh?
bob
Western mints received metals from a very wide geographic area. San Francisco covered all of the west coast states plus Alaska, western Canada, and Baja California. Denver received silver and gold from central Canada, Montana and southward into central Mexico. New Orleans silver came from Mexico, Central America and parts of South America - much of it smuggled out of the countries and into the US.
Deposits were weighed and assayed separately, then combined for refining. Metal that was not refined, such as at Denver, was shipped to Philadelphia and New York for bulk refining.
I can't speak specifically about US silver, but I can relate some inside info on other precious metals.
When I worked for GM on catalyst development, they were paranoid that someone could potentially steal some of their platinum, palladium, and rhodium that was destined to become part of a catalytic converter. I was told that trace elements (either natural, or purposefully added) would yield a "fingerprint" when analyzed. Of course, this was a closely guarded secret. They did NOT buy ingots or bullion like we are used to seeing in the bullion market. I know of only one lawsuit that utilized the "fingerprint" data.
I think this paranoia faded after no significant problems were encountered. They ultimately opted to go with a more standard fineness of 0.99999 pure (5 nines) which made trace elements much harder to analyze with accuracy.
We did see differences in impurities between Russian, South African, and US mines.
Reminds me of a funny encounter with a GM accountant. He wanted us to keep rhodium metal inventory to the penny and report each week. We had several forms of work in process material - from rhodium sponge (5 nines high surface area metal) to rhodium salts in solution, to reclaim materials from the process. In the early '90s rhodium spiked to over $5k on the spot market. I showed him a milligram of rhodium sponge - about 15 cents. He couldn't even see it....... We didn't have the proper equipment to run the analysis anyway....
I loved messin' with the GM CPA's and lawyers - totally non-technical.
“In matters of style, swim with the current; in matters of principle, stand like a rock." - Thomas Jefferson
My digital cameo album 1950-64 Cameos - take a look!
There has been a recent surge in doing isotopic analyses of coins to understand sourcing of the metal and what is means for the economies and histories of the past. The first paper to do this recently was published by Francis Albarade of école normale supérieure de Lyon in Geochemical Perspectives, a new journal with open access ran by the European Association of Geochemistry. I wish I would have seen that talk with these new results - we had 4,000 contributions at that meeting in Paris and alas, I was not aware of this one. I wish I could get my lab into the foray, we would have to find out what questions we could answer and if we can source the silver. Problem is, these types of analyses are time consuming and costly. If someone can fund me for about $50-100K, we could do the gold rush - I suspect though that you could find records of silver sources for the San Fran mint without having to spend that type of money (see Roger's post above). The main focus so far is analyzing ancients. Many more wide open questions to be examined with ancients, as the NN article shows.
Now isotopic fingerprinting of 18th century US gold might be very interesting.......
Best, SH
Actually Pb, Os, PGEs, all in ppm quantities will pass through the refining process. More than enough to analyze for isotopes and abundances for isotope fingerprinting. All you would need is a couple mg's (or even less) of the coin to do the work. But you are right about the adding of copper, that would like overprint the Pb completely, but maybe not the Os and PGEs. In either case, you would likely get a hybrid signal that is not much use. HST, doing the Cu isotopes would likely provide some source info for the Cu.
Best, SH
I would think that tracing, or confirming, the source of gold for locally produced coins, (i.e. Cal gold, Mormon gold) might be relatively easy. Performing the same for high runs of Mint specific gold may not be possible since the source gold may well have come from multiple areas. Cheers, RickO
It would probably be a lot easier if gold and silver had more isotopes. It would be more direct to look at the isotopic composition of the gold and silver themselves. But gold, for example, has only one stable isotope, Au-197, and so gold has no isotopic fingerprint, it is literally all the same. So you would have to analyze the impurities. Silver does have two isotopes, so it has a little signature, but I'm sure it would be nicer if there were more.
A lot of old coins were recycled at the mints, and some of those new coins then got recycled at other mints. Think about the Smithson Bequest, which arrived from Great Britain in the form of sovereigns (possibly from one source of gold, possibly from a thousand sources of gold) to fund what became the Smithsonian Institution.
Even though they were all re-circulable in the British Empire, the U.S. converted them into U.S. gold coins which were spent to build the first building, hire staff, etc. The coins accumulated in various banks. If, just a few years later, some of those coins were sent back to England to purchase goods or cover a trade deficit, the Royal Mint would have melted these AU U.S. coins down along with whatever French, Russian, Peruvian or Japanese gold that the Bank of England had accumulated in the meantime and converted them all into Sovereigns because obviously British gold was superior to everybody else's gold.
RE: spacehayduke.
To add to the poster's comments....Assay records exist for the mints covering many years, although they are spotty. While not to modern standards, trends can be observed. Also, if you check you copy of From Mint to Mint, Chapter 1, you'll find general information from Jacob Reese Eckfeldt, William Ewing DuBois, and Joseph Saxton, on the characteristics of gold from various sources. The mint assay records are more detailed.