Author Topic: Metallurgical analysis of Roman coinage (Read 2926 times)

Nickolas P · « **on:** November 20, 2016, 05:20:47 pm »

Hello everybody, new member here, with information which may be of interest to others.

I sent 7 Roman coins to IMR TEST LABS (Curtiss-Wright) in order to learn what metals were used in the alloys.

2 denarii from Trajan, COS IIII, a silver tetradrachm from Trajan, COS V, mint of Tyre. These coins were bought from Forum Ancient Coins.
1 potin tetradrachm from Aurelian-Vabalathus, Year 5 Vabalathus.
1 potin tetradrachm from Aurelian. Year 4.
1 potin tetradrachm from Probus. Year 6.
1 potin tetradrachm from Maximian. Year 5.

The report is 147 KB, in PDF format, which is considerably over the 9000 KB per post limit, and PDF is a not-allowed format. Is there any way to post this report? It's interesting.

Thanks for any response.

N.Paglia.

traveler · « **Reply #1 on:** November 20, 2016, 09:40:15 pm »

Hi,

What was the method of analysis used?

Nickolas P · « **Reply #2 on:** November 20, 2016, 09:45:23 pm »

The method of analysis was XRF, (X-Ray Fluorescence), presented via Energy Dispersive Spectrometry, as per ASTM E1916-11. The results are given in percentage by weight, of each element found to be present in the coin.

traveler · « **Reply #3 on:** November 20, 2016, 09:55:47 pm »

Hi,

Unfortunately XRF analysis is generally understood to be unreliable for ancient coins, including the denarii of Trajan you sent to the lab. You can read more from the extracts of this book.

https://books.google.com.sg/books?id=aBVoBgAAQBAJ&pg=PA84&lpg=PA84&dq=butcher+and+ponting+xrf&source=bl&ots=TIIYuI3-NY&sig=6urCy4Uz2VRgsYeF-aUwJmaFGH0&hl=en&sa=X&ved=0ahUKEwjquvjU6rjQAhWBtI8KHRtsBScQ6AEILDAD#v=onepage&q=butcher%20and%20ponting%20xrf&f=false

Nickolas P · « **Reply #4 on:** November 20, 2016, 11:10:26 pm »

Point taken, and I'd add that rather than drilling a small hole into the coin (destructive testing) why not just go OES, and vaporize the entire coin? Either method is destructive, but OES will provide the absolute answer, across and through the entire specimen. XRF has come a long way in the last 10 years, it's not 1950's XRF, or even 2005 XRF.

I'm now thinking to OES the Alexandrian tetradrachmae, but not the silver from Trajan, as it is museum-quality, beautiful coins in an excellent state of preservation, bought at Forum Ancient Coins. See how the results from XRF and OES examination, differ, using the very same coins, still at the lab.

Thank you for your response, because I intend to keep testing more coins, and such an effort requires collaboration. I can't think of a better venue in which to continue this project, and Joe Sermarini has graciously agreed to host it, but simply hasn't the time to "work it." We have access to a Scanning Electron Microscope, and Neutron's, aside from XRF, OES, and Laser Ablation.

Vale.

N.Paglia.

traveler · « **Reply #5 on:** November 20, 2016, 11:32:25 pm »

Hello,

I'm not sure what OES stands for, but I assume you mean melting the whole coin and testing the results for metal composition?

Butcher and Ponting did cover why the reason why they didn't do so. Firstly the surface silver of the coin was often deliberately enhanced through silver depletion. Burial over centuries will also achieve the same effect to some degree. Therefore melting the entire coin and measuring the results will give a higher figure than the original alloy.

Secondly, and more practically, it will have been untenable to melt large numbers of ancient coins in good condition for testing.

Nickolas P · « **Reply #6 on:** November 21, 2016, 12:14:16 am »

Hi Traveller,

OES is Optical Emission Spectrometry, and one doesn't melt the coin, the coin is actually vaporized, all of it, or whatever section(s) are selected. It's very exact, whatever and however the Elements from the Periodic Table of Elements turn out to be, and got there, they're there. It's up to the Roman coin enthusiasts to figure out how and why. I'd gladly pay for another test, of the same coins, but not exactly the ones that I have. Prieur 1496, or any of the others, if you have one, we'll test it, see how it compares to mine, same XRF analysis, same lab, and same humans.

Like I said, it's a collaborative effort. Check you e-mail, I sent you the XRF results from IMR.

Vale.

N.Paglia.

SC · « **Reply #7 on:** November 23, 2016, 05:25:09 pm »

I would like to read your report as well. Though it is over the usual posting limit, maybe there is a way to send it to be uploaded as a pdf on the site - on the wiki or main page???

XRF is not unreliable, just limited in what it can do. If done properly each technique can provide some information. The devil is in the details. XRF is generally a surface analysis technique. It does not plumb very deep. If done on a unprepared coin then you are in reality analyzing the patina. If done on a coin with some preparation, like surface scraping, then you analyze the outer part of the metal. While the potin tetradrachms were apparently never silvered, the metal near the surface will still not be entirely the same as the core or heart metal.

On the other hand methods like AAS that can get to the heart metal do not take surface changes into account. And this can be important when silvering or surface enhancement/depletion was purposely done.

And as noted total destruction techniques, whether OES or the older "wet analysis", analyze the whole coin - but only the whole coin of today which is different from that of 2000 years ago.

So as long as you know and take into account the limits of each test, and they are carried out using proper equipment and methodologies, all tests add valuable new data.

Shawn

Robert_Brenchley · « **Reply #8 on:** November 24, 2016, 05:33:05 pm »

Is there a way of scanning the whole cross-section of a cut coin, in detail?

Nickolas P · « **Reply #9 on:** November 24, 2016, 07:34:48 pm »

Yes, there is a way to scan a detailed cross section, which is exactly what we're going to do with the four Alexandrian tetradrachmae. We are going to saw them in half, experiment on one half, and save the other. A Scanning Electron Microscope (SEM) will be used, and the actual microstructure of these coins will be revealed, from surface to surface, through the core, and at all points encountered along the way. As well the principles and practice of OEM (Optical Emission Spectrometry) and ICP (Inductively Coupled Plasma) will, or can be, applied.

It will be interesting to see how these upcoming results, interact with the results from the original XRF surface inquiry.

Thank you for your input, think of some good questions. Based upon the XRF results, I have a lot of questions, so if you can think of anything, SPEAK UP, this can only be a collaborative effort. The size and format of the XRF results (148KB in PDF) are not "supported" by Forum Ancient, but I'll e-mail them to you if you'd like, and if you can figure out how to make this data available to all Forum members, please do so.

Robert_Brenchley · « **Reply #10 on:** November 25, 2016, 04:57:28 pm »

Yes, I'd be interested, thanks. I'm decidedly no expert though!

jmuona · « **Reply #11 on:** November 25, 2016, 05:27:57 pm »

The main reference to this interesting subject is:

Butcher, K., & Ponting, M. (2014). The Metallurgy of Roman Silver Coinage: from the Reforms of Nero to the Reform of Trajan. Cambridge: Cambridge University Press. Retrieved from http://www.cambridge.org/9781107027121

Anyone interested in the field should really read it.

The interesting thing is the metal composition of the planchet when the coin was minted, like Shawn pointed out. The metal composition today depends on the corrosion that has taken place after that. The present composition of the whole coin can be examined without destroying the coin. The point is that this piece of information is not that useful, as we do not know what has taken place and consequently do not know what the coin was like when produced.

Jyrki Muona

Nickolas P · « **Reply #12 on:** November 25, 2016, 06:02:53 pm »

Robert Brenchley, how do I send the XRF report to you?

J.Muona, thank you for the input. I have just ordered two copies of the book, one for myself, and one for the lab-crew at IMR. We will probably never know the exact original chemical composition of these coins, but we can know their composition as they've come down to us, and perhaps learn more about the manufacturing process.

Paglia.

timka · « **Reply #13 on:** November 26, 2016, 03:10:58 pm »

Hi Nicolas,

I have a broken silver siliqua of Constatius, which I can contribute to your research, if you are interesed. It is so crystalized and fragile as dried leaf, so it did not survive the shipping. It is good for research only as it is now. So, if you are interested, let me know where to send it.

The picture is below.

Cheers,

Z.

Robert_Brenchley · « **Reply #14 on:** November 26, 2016, 04:47:55 pm »

I've sent a message.

Joe Sermarini · « **Reply #15 on:** November 26, 2016, 05:22:23 pm »

I can upload PDF's to the server and provide a link. Send it to me by email.

Nickolas P · « **Reply #16 on:** November 26, 2016, 07:43:07 pm »

I've sent copies of the report to all whom requested one.

Timka, a crystallized, shattered siliqua would be an excellent candidate for microstructure analysis, send the coin to:

IMR TEST LABS
attn: Brian Herndon
4510 Robards Lane
Louisville, KY, 40218

Your coin will not be further destroyed unless you say so, and will be sent back to you, with the formal findings. That was a well preserved coin. Thank you for submitting it.

Thank you Joe, for hosting this project on your website.

N.Paglia.

Joe Sermarini · « **Reply #17 on:** November 27, 2016, 10:21:33 am »

The lab results are here:

https://www.forumancientcoins.com/numiswiki/documents/201602910_Nickolas_Paglia.pdf

Nickolas P · « **Reply #18 on:** November 27, 2016, 04:11:17 pm »

Thank you Joe.

Joe Sermarini · « **Reply #19 on:** November 27, 2016, 07:08:47 pm »

Thanks for sharing Nick.

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Author Topic: Metallurgical analysis of Roman coinage (Read 2926 times)