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 Replies: 10 / Views: 1,379 |
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Pillar of the Community
United States
685 Posts |
I want to submit a Mexico 1789 8R for XRF testing to determine the levels of silver, copper, gold, and platinum in the coin. The objective is to gain insight as to when the coin was made, and by extension, its authenticity.
I queried a couple companies in the area (Southern California) about their capacities. My question:
"...I want three XRF shots, front, back and edge of the coin, and need to know the silver, gold, platinum, and copper content of the coin. To what PPM will the results show?"
The response from the XRF testing vendor:
"...Regarding the sensitivity (the what ppm question), in the case of lead in silver I would expect somewhere in the 0.01% range (100 ppm). I can see lead in copper down in the 50-70 ppm range. With Gold and Platinum, I may have to give a rough estimate based on a visual interpretation of the spectrum because there are cutoffs built into the software to avoid false positives. (Gold and Platinum are in the quantitation, but the manufacturer of the units assumes that if you see them, they will be in a karat alloy). I would expect to be able to see the lines in the several hundred ppm range."
OK I am confused. Is the response from the XRF testing vendor above sufficient to ID the timeframe of manufacture of this coin? If not what questions should I be asking? What are the minimal criteria for analysis? Maybe, what machine should be used for the analysis?
Any help would be appreciated.
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Valued Member
United States
266 Posts |
My interpretation, is the Au and Pt levels in question is below the range of his calibration curves, that's why he will only be able to offer an estimate based on the spectrum. If his data is adequate for your needs depends on the data you will be comparing it to, It depends on how precise the known values are and the differences between the different mines.
What type of XRF is he running?, Energy dispersive, wavelength dispersive? is it a small table top unit of a full powered research grade?
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Pillar of the Community
United States
1247 Posts |
You should contact Abigail Sciuto 27130 Telegraph Road Quantico, VA 22134  |
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Pillar of the Community
United States
5362 Posts |
ColonelJohn would be able to tell you - he did all the studies for our book and developed the data on Au and PT levels in older Mexican silver.
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Pillar of the Community
United Kingdom
2490 Posts |
colonialjohn even 
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Pillar of the Community
Hong Kong
1270 Posts |
Westwood Arms, would you show us the pictures of your coin before sending it for XRF analysis?  |
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Valued Member
United States
462 Posts |
Does TPG graders use XRF to determine the authenticity ? Also are these details of composition for old coins (say European crowns)listed some where for us to look up ? |
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Valued Member
United States
266 Posts |
I doubt it, analyzing a coin is very difficult, the counts you will get is dependent on surface area, normally an XRF sample is ground smooth with a specific grit of sand paper, giving a fairly consistent surface area. This is not something you will want them to do to your coin. the only practical thing to do will be use a mask to only analyze a flat area such as one of the fields, but the smaller the area analyzed the larger the error. Also the surface area will still vary with the amount of wear, scratches and dings. You need the unknown samples surface area to match the calibration standards area to be able to really have any reliable readings.
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Pillar of the Community
France
1591 Posts |
Rdwarrior : you are guessing here, this is not fact ;) Actually, TPG are getting some hardware to do XRF analysis, what's unknown is : which coin they are analyzing, what's the hardware used, what's the procedure used to check the coin. But at least NGC is advertising this on their site. As for wether it's accurate or not, you can find very long threads with CollonialJohn and Swamperbob discussing about those recent tools in order to authenticate the alloy used to make coins (and compare it to techniques used back then to make them). Indeed, the test should be done with care, on a properly calibrated device, in multiple areas (edge + two clear places is nice). Jeweler's device used to just check gold / silver content are not accurate enough (or at least, not calibrated for a properly made analysis for a coin - checking about 8/10 different metals in the alloy) Here is an XRF result from CollonialJohn on one of my coin, which seems to be a sheffield plate - this was checked on an oxidized area of the coin (as well as 3 other places) : Ag 55.11 Sn 0.80 Fe 0.10 Co 0.03 N 0.04 Cu 45.04 Zn 0.35 Pt 0.14 Au 0.22 Hg 0.38 As 0.14 Pb 0.69 Bi 0.24 |
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Pillar of the Community
United Kingdom
2490 Posts |
It's a tribute* to Mrs Redfern, my chemistry teacher 50 years ago, that I didn't have to look any of those up. 
*And a huge surprise to me too. |
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Valued Member
United States
462 Posts |
Mathieuma, does your coin rings like silver and magnets slides off of it quickly ?
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Replies: 10 / Views: 1,379 |
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Posted 12/16/2013 6:34 pm
