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FORVM`s Classical Numismatics Discussion Board  |  Numismatic and History Discussions  |  Ancient Coin Forum (Moderator: goldenancients)  |  Topic: Determining Metal Content 0 Members and 1 Guest are viewing this topic. « previous next »
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Molinari
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« on: August 22, 2018, 06:00:31 pm »

How large of a sample is needed to determine the metal content of a coin, as in the specific breakdown (% copper, % lead, % gold, etc.)? Is it a difficult and expensive process?

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PeterD
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« Reply #1 on: August 23, 2018, 04:40:40 am »

The preferred method is to drill a small hole into the rim of the coin in order to reach the unadulterated alloy in the centre of the coin. I would suggest reading the first few chapters of Butcher and Ponting's  book "The Metallurgy of Roman Silver Coinage", where the whole process of testing is described.
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jmuona
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« Reply #2 on: August 23, 2018, 04:55:08 am »

Depends on the coin type, but if you wish to get the trace metals and even the isotops, it definitely costs a lot. Many ancient coins have lost the original composition from the surface layers and you need to drill a hole from the side and use the turnings from deeper inside to get an idea of the original situation.
There is always variation within coin types and between mints and dates so single coins might not tell that much. With both gold and silver coins I strongly recommend consulting the recent book by Butcher and Ponting: The metallurgy of Roman silver coinage. The techiques needed for accurate analysis require access to very expensive equipment.
If you only need results of high silver content (or gold) coins, then surface studies suffice and would be much cheaper. However, even then you need help from a lab.
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Joe Sermarini
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« Reply #3 on: August 23, 2018, 05:19:09 am »

I have handled some of the coins tested for Butcher-Pointing (coins from the Jyrki Muona collection). I think the drilled hole is so small that it does not detract from the coin at all. In fact, I would prefer a coin with the hole and test results to a coin without the hole and test results. My only exception might be a great rarity in mint state. I wish it was cheaper and hope more studies are done.
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Molinari
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« Reply #4 on: August 23, 2018, 06:46:47 am »

Thanks for the responses.  One of our members, Ed Snible, suggested on a different board that the large bronze coins from Rhodes might have been struck using metal from the colossus after it had fallen.  This could perhaps be a testable hypothesis since the large bronzes were minted over a fairly long period.  Presumably, the metal analysis might indicate that all the coins derive from the same source, assuming the metal wasn’t modified after being torn from the statue.

You’d need a large sample, however.  Maybe someday when the process is less intrusive it could be explored.
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« Reply #5 on: August 23, 2018, 07:19:43 am »

And only if the bronze of the statue was homogeneous. If the bronze came from different sources, the composition may also differ.
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Molinari
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« Reply #6 on: August 23, 2018, 07:42:42 am »

True.  Legend has it that the metal comes from the spoils of war after a particular battle.
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« Reply #7 on: August 26, 2018, 12:41:25 pm »

For XRF tests on ancient coins drilling holes is overkill in most cases. The composition of surface corrosion is mainly due to the effects of light elements from the periodic table (oxygen, sulfur, carbon, etc.). X-rays pass through these elements easily so, again in most cases, they're not figured in the results. The margin of error on XRF analyzers is in my opinion too wide to allow one to deduce geographical origin data with any sort of reliability. Especially considering that ancient coins were often made from older coins.

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JBF
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« Reply #8 on: August 26, 2018, 04:04:12 pm »

I have heard of some kind of laser(?) scanner that coin stores sometimes have to detect whether gold and silver objects are what they "should be" or not.  Can anyone tell me about that, yes, I do not know what I am talking about, which is why I am asking.

I don't think that it would be useful for what Molinari hopes for.  On the other hand, if you find a dealer in the neighborhood, he might just let you play around with it for free.  Especially if you cite his name as a contributor to furthering knowledge in any publication you might make.
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n.igma
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« Reply #9 on: August 26, 2018, 10:47:21 pm »

I have heard of some kind of laser(?) scanner that coin stores sometimes have to detect whether gold and silver objects are what they "should be" or not.  Can anyone tell me about that, yes, I do not know what I am talking about, which is why I am asking.

I think you may be confusing this with a hand held XRF (X-Ray Fluorescence) analyzer that is held by some jewelers and  pawn shops to analyze metal content.

https://www.bruker.com/products/x-ray-diffraction-and-elemental-analysis/handheld-xrf/applications/xrf-precious-metals.html
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« Reply #10 on: November 08, 2018, 02:24:24 pm »

XRF IMO is one of the best way to determine authenticity and even the geographical mint area in some cases. I give an example. I bought 3 coins as below:

1. Parthian Arsaces I mint of Hecatompylos circa 200 BC
2. Sassanian Shapur III Herat mint circa 380 AD
3. Sassanian Ardashir I no mint

I tested all these with XRF and found all three had very close readings of trace elements for gold and lead (Au ~ 0.7%  Pb ~ 0.1%) Now we know geographically Herat and Hecatompylos  are both close to modern afghanistan area so my conclusion was the Ardashir coin was also minted in same area as the trace elements shows the mine they used would be the same .
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« Reply #11 on: November 11, 2018, 01:19:11 am »

I think it would be necessary to know the composition of the originals for the analysis to be useful.
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JBF
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« Reply #12 on: November 11, 2018, 04:58:27 pm »

years ago there was an appeal on a listserv for samples to use for analyzing composition of incuse coins of Magna Graecia,
I am wondering if anyone knew or had the results from such tests.  I believe it was being conducted out of Australia.
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n.igma
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« Reply #13 on: November 12, 2018, 03:32:54 am »

A multi-technique investigation of the incuse coinage of Magna Graecia. Journal of Archaeological Science 20 (2018) 748-755
by  F. Salvemini, K. Sheedy, S.R. Olsen, M. Avdeev, J. Davis and V. Luzin

Abstract: This paper focuses on the application of different neutron techniques to characterize the manufacturing process of 'incuse' coins minted by Greek colonies in Southern Italy during the 6th and 5th centuries BC. In order to provide an insight into incuse coinage minting, numismatic and historical studies were combined with metallurgical research based on non-destructive neutron diffraction, neutron texture analysis and neutron tomography. The most significant scientific data collected during our campaign of investigation will be showcased.

Download available here : https://www.academia.edu/37383774/A_multi-technique_investigation_of_the_incuse_coinage_of_Magna_Graecia._Journal_of_Archaeological_Science_20_2018_748-755

It is focused on manufacturing technology rather than metal chemistry.

An interesting related paper Neutron tomographic analysis: Material characterization of silver and electrum coins from the 6th and 5th centuries BCE
https://www.academia.edu/25818129/Neutron_tomographic_analysis_Material_characterization_of_silver_and_electrum_coins_from_the_6th_and_5th_centuries_BCE._Materials_Characterization_2016
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JBF
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« Reply #14 on: November 12, 2018, 01:44:08 pm »

Thank you for finding it.  I was hoping it could tell something about the origin of the silver for the M.G. incuse coinage.  I guess I misunderstood its topic.
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