Metallurgical Analysis of Collectable Coins: What is Involved?
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Reading another post here I began to wonder about the process of metallurgical testing for collectable coins.

 

I can't find too much online about the actual process. Does anyone know what is involved?

 

How different is the metallurgical testing of collectable coins (done by a company like NGC) from the testing of coins at a mint? I'm assuming that mint assayers don't have to worry too much about damaging a coin; unlike NGC.

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In my younger years I was a steel buyer for a spring mfg. corp. and a lot of our sales were govt. contracts which required verification of the composition of the metal used. To have the material analyzed, required removal of some of the material and sending it to the testing lab. It would seem to me that the same process would be used to analyze a coin which would damage the coin.

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I believe that NGC offers a metallurgical analysis service, most useful for patterns and such. My understanding is that they use spectroscopy, which is not harmful for the coin.

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I received a MS coin back from NGC after this test and there were no marks on the coin when It was returned.

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I was thinking they might be able to identify the surface metal by it's atomic structure with an electron microscope. But have no clue how they're able to identify the core material. X-ray spectroscopy?

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X-ray spectroscopy?

 

Yes....

You can even purchase hand-held units today for about 12 G's....

 

Paul

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There are several different ways of doing metallurgical analysis, some are destructive to the piece and some aren't. The non-destructive bombards the sample with either x-Rays or neutrons. In the case of the X-ray analysis the atoms in the sample absorb the X-ray energy exciting some of the electrons to a higher energy state. When the electron return to the lower state they emit photons characteristic to that particular element. The frequency of the photons tell you what the element is, and the relative strength of the emission tells you the amount of the element present.

 

Neutron analysis works similarly except instead of just photons you are looking for other particles as well, neutrons, electrons , possibly even gamma rays, protons and positrons. In each case the re-emission of the elements after they absorb the bombarding neutrons. Again the characteristic energies on what is re-emitted tels you the element and the strength of the emission tells you the amount .

 

X-ray analysis is cheaper and faster but has the drawback that it only tells you about the surface composition down to maybe a couple of microns. Neutron analysis penetrates deeper but takes longer, costs more, and depending on what elements you have present could result in a slightly radioactive sample for awhile.

 

Typically for coins X-ray analysis is used. It used to take special labs and half million dollar electron microscopes to do the anaylsis, but today they now have hand held devices that cost several thousand dollars (That can often be rented for a couple hundred dollars a month) that can take the readings in a matter of seconds. They report the elements present and their percentages. These can test coins right through the holders they are in so you can test a coin while it is still in a slab.

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There are several different ways of doing metallurgical analysis, some are destructive to the piece and some aren't. The non-destructive bombards the sample with either x-Rays or neutrons. In the case of the X-ray analysis the atoms in the sample absorb the X-ray energy exciting some of the electrons to a higher energy state. When the electron return to the lower state they emit photons characteristic to that particular element. The frequency of the photons tell you what the element is, and the relative strength of the emission tells you the amount of the element present.

 

Neutron analysis works similarly except instead of just photons you are looking for other particles as well, neutrons, electrons , possibly even gamma rays, protons and positrons. In each case the re-emission of the elements after they absorb the bombarding neutrons. Again the characteristic energies on what is re-emitted tels you the element and the strength of the emission tells you the amount .

 

X-ray analysis is cheaper and faster but has the drawback that it only tells you about the surface composition down to maybe a couple of microns. Neutron analysis penetrates deeper but takes longer, costs more, and depending on what elements you have present could result in a slightly radioactive sample for awhile.

 

Typically for coins X-ray analysis is used. It used to take special labs and half million dollar electron microscopes to do the anaylsis, but today they now have hand held devices that cost several thousand dollars (That can often be rented for a couple hundred dollars a month) that can take the readings in a matter of seconds. They report the elements present and their percentages. These can test coins right through the holders they are in so you can test a coin while it is still in a slab.

 

Excellent information. Hand held XRF spectrometry devices are widely used to assay metal content.

 

See here http://www.bruker.com/products/x-ray-diffraction-and-elemental-analysis/handheld-xrf.html.

 

There was an earlier thread, on this forum, which I will try to find, that demonstrated that coin composition analysis by XRF spectrometry while very accurate, was affected by TPG holder plastic resulting in some very confusing metalic analysis results. The holder plastic refracted the return signal resulting in false readings of metals present in the sample.

 

I think Messydesk may have info on this subject.

 

Carl

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I work in Aerospace and we have a X-MET 5100 in my lab. It is fun to use and check coins with. I like to check the ancients to see what they are made of. Recently started getting into gold nuggets so went ahead and zapped them also to make sure they were good. Doesnt hurt the coin or leave marks. Just good ol radiation.

147477.jpg.c8761c5b670bf1710145e8107431b0ae.jpg

147478.jpg.1d7cf137f41ed67a46d7bef4847c443c.jpg

Edited by BrokCoinCollector

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Wow, that thing is awesome.

Maybe in 10 years we'll have a x-ray spectroscope app on our iPhones.

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I hope not. Can you imagine the average person out there with devices that can blast anything or anyone with x-rays?

 

"Look at my new necklece! It's real gold!" and all her friends one after another put their Iphones up to her chest and blast her with their spectroscope apps. "And my new earrings!" This time all the Iphones go up to her head. And so on.

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I hope not. Can you imagine the average person out there with devices that can blast anything or anyone with x-rays?

 

"Look at my new necklece! It's real gold!" and all her friends one after another put their Iphones up to her chest and blast her with their spectroscope apps. "And my new earrings!" This time all the Iphones go up to her head. And so on.

 

Sorry, after further thought, deleted for lack of good taste.

Edited by okbustchaser

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At the FUN show this year, there was someone with an X-ray spectrometer doing demonstrations for people using real and fake coins, both raw an in slabs. I think the price on the unit was $17K. Would seem like a must-have for shops that buy scrap. A couple of us rounded up a bunch of the counterfeit micro-O Morgan dollars for testing. Most came up as Sterling silver, but a few were 90%.

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On 20/05/2014 at 9:51 PM, BrokCoinCollector said:

I work in Aerospace and we have a X-MET 5100 in my lab. It is fun to use and check coins with. I like to check the ancients to see what they are made of. Recently started getting into gold nuggets so went ahead and zapped them also to make sure they were good. Doesnt hurt the coin or leave marks. Just good ol radiation.

147477.jpg.c8761c5b670bf1710145e8107431b0ae.jpg

147478.jpg.1d7cf137f41ed67a46d7bef4847c443c.jpg

Hello Sir,

We also have a X-MET5100 but it has a problem and we need "service password" for it. Could you please let us know the service password if you have it?

Marry Christmas and have a very happy new year

Kajo

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On 5/20/2014 at 11:37 AM, thebeav said:

 

Yes....

You can even purchase hand-held units today for about 12 G's....

 

Paul

I'm almost certain this is what is used by NGC. They have stated that the process is harmless and can actually be done through the slab, if necessary. I've seen these devices as cheap as 10k!

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I just received my coin back from NGC  after a so called metallurgical analysis. The paperwork received gives the "XRF Elemental Analysis" separately for the obverse and reverse of the coin. It has a disclaimer at the bottom that results are based on "surface analysis only and do not reflect the composition of the core, which may be of different alloy." The two "Report of Analysis" documents, along with the web-based description of the Metsllurgic Analysis services imply that the entirety of the surface is scanned in the analysis, which is the only thing that would be useful and remotely worth the $75.00 service fee. However, in an email from NGC regarding my submission, NGC admits that only a "spot" on each side is scanned, which renders the conclusion meaningless in terms of overall surface composition, both because the measurement of the spot scan is undefined and because different spots could be entirely different. The service therefore useless and quite frankly false advertising. In my case, I was told that the reverse of my 1945 S Lincoln penny was 82% copper, 13% silver, and 4.5% zinc and the obverse was the no normal 95% copper and 5% zinc. These results can't be accurate, as the High Definition photos I paid NGC to take clearly show to the naked eye that the surface of the reverse is more than 13% silver and the obverse surface contains something amount of silver. NGC response to this was that only a "spot" on each side of the coin was tested. NGC refused to grade this coin by stating that it's NGCs position that the reverse had been electroplated with silver after leaving the mint. Even ignoring the silver bleeding through the obverse side, which appears to be the opposite (copper electroplated over silver), still how can NGC state that anything has been electroplated if it doesn't analyze the core? I did receive a partial refund, which I appreciate, but I am disappointed in NGC's shoddy analytical methodology of "spot" testing and its unfounded conclusions regarding electroplating without any core analysis. I am in possession of over 40 Lincoln pennies which have privately tested positive for silver content and was hoping to use NGCs metallurgical services to verify the exact composition, even if only for the surfaces. Now knowing that NGCs results would not be meaningful at all, I have to find a real lab to give me an accurate, meaningful, and therefore useful analysis of the surfaces or entirety of my pennies. NGC needs to either put the "spot analysis" disclaimer on its web description or commit to giving an entire surface scan so that these percentages are useful to people. NGCs metallurgic analysis service is a waste of time and money as currently configured.

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4751961-001r.JPG

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A typical test produces results for the area examined. Also, the percentages are approximate composition within the measured spot, not the entire surface. The obverse measurement was likely of a portion of unplated metal and showed a more-or-less typical composition. The reverse measurement of 82% copper, 13% silver, and 4.5% zinc indicated the average composition within the measurement spot, and also confirmed that the silver plating is very thin. (XRF penetrates slightly depending on beam energy.  Accurate calibration is also imperative.)

No XRF measurement will produce a bulk metallic analysis; neutron activation will do more but not definitively come back with "normal cent alloy; silver plated."

The results are, in my opinion, very useful. However, it requires a certain amount of experience to interpret the raw XRF results, particularly in context with other measurements and observations. That is, physical measurements and observations are parts of a complete examination and attribution of the coin or other object.

Consider this: If the XRF beam were a full 3/4-inch in diameter and covered the entire face of the coin, the result would be an average of the entire surface. Thus, the average for the obverse might have been 10% silver, and the average for the reverse possibly about 75% silver. Neither of those tell us the metallic composition of the coin - only the average surface. Both full-area measurement would have been useless except to show the approximate portion of the surface covered by silver.

XRF is not point-n-shoot technology either in measurement or interpretation of output.

Edited by RWB

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