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Pillar of the Community
 United States
4883 Posts |
Quote:
What about minor components. Was the XRF device sensitive enough to detect any gold? I had hoped to see some trace gold to verify its pre-1850 origin, but according to colonialjohn, the particular apparatus used will not pick up metals that comprise less than 0.5% of the overall composition. Colligo ergo sum
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Pillar of the Community
United States
4883 Posts |
You may have noticed that the first 1833 here (for which I posted the pics right after I got it) was pretty loaded up with green gunk, probably from improper storage within a reactive medium. That's since been washed away with acetone, so I thought I'd post updated images. The distinctive "barred" or "bridged" threes are especially prominent on this specimen.   Colligo ergo sum
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Pillar of the Community
United States
5362 Posts |
Regarding the use of XRF to test for gold, you need to exercise caution when looking at the results. You can easily infer too much by reading into the tests things they really do not say.
Silver contained in counterfeits made at the same time as genuine coins should contain the same or similar trace contaminants as genuine coins provided the silver was drawn from the same location.
To explain further, lets say these 1832 and 1833 coins that test low in silver are counterfeit with a silver content of 80% instead of about 90% - the trace contaminants should appear in ratios of 8/9 ths or about 89% as much trace contaminant as a coin made of genuine silver from the same area. So the source of silver used by the counterfeiter is what is being tested. Coins made in the mint with an alloy that was short in silver would be IDENTICAL in all respects to genuine full alloy coins from the mint.
If the counterfeiter used silver from melted coinage and he was located near the mint - it is very likely that the silver signature is very similar.
If the counterfeiter was actually located in New York City the signature could be quite different depending on his silver source.
Another critical thing to keep in mind is that if there is significantly less silver in the counterfeit say 50%, you need to remember that you are looking for one half of the level of trace contaminants in the silver signature and as many as 4 times more contamination from the copper source.
So XRF signatures will depend where the counterfeit was made as well as when it was made. If the counterfeits are found primarily in Mexico it is more possible that native Mexican silver was used because the coins were likely made there. However, a similar counterfeit made in the UK (Birmingham) likely used silver available in that location. History tells us that silver mined in the UK came from lead deposits but it also tells us that England captured many Spanish ships with cargoes of silver coming from Mexico, Peru and Bolivia in the time period of about 1800. Therefore the silver signature of a UK counterfeit could display any of 4 or more contamination patterns.
The take away from this and the only factor at this date that can be stated strongly is that pure silver (0.999 fine) and pure copper (0.99 fine) were not available in large monetary quantities before 1850 (UK for lead silver only) and 1870 (US for Nevada silver). After 1890 silver worldwide reached purity of 0.999 or better. I expect all silver coins that were actually produced before 1850 to be contaminated. Coins made after 1850 may contain high levels of contamination if older refining methods were used.
KEY POINT - Coins made from essentially pure metals are products of the late Nineteenth and Twentieth Centuries. This is the point that you need to recall when assessing laboratory test results.
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Pillar of the Community
United States
1757 Posts |
Unfortunately the apparatus at my company now are around 20+ years old so we normally have an instrument detection limit of 0.5% and are wary of the accuracy below 1%. For our work this instrument is good enough so to speak. When at EDAX/Spectro I was working with accuracy down to 0.01% and IDLs of 0.001% such as on the EDAX Orbis for testing I provided Gurney in his book BIG DIFFERENCE. Again, low trace signatures are fine to make general assessments as with gold levels and time of manufacture - but be careful when we are talking provenance to a certain mint. Lead isotopic analysis (LIA) is the main tool now used to provenance coins to particular mints as this was started around 1967, even today in 2017 recycled metals are a problem for coins dated 1500-onward to particular mints with very high certainty. What they generally do now is do a LIA study on the surrounding in-ground ore deposits first in a region or around a particular mint in question and then compared the LIA ratios to that of the coin in question and see how they MATCH UP. Works great for ancient coinage if we just wish to verify a suspected known mint to a particular coinage since recycling of metals may have not occured as with later post-1500 operations - so it gets complex after 1500 or so due to the recycling metal factor ... they are also using copper isotopic analysis recently also as a tool for provenance with promising results. For those who know this coinage determining if the copper ore around Simsbury, Ct. was used for the infamous Higley Coppers would be a good project. Dr. Freidus (known authority on Higleys) never could and another argument they simply did not have the technology to purify the ore for this rare issued coinage but it was still exported due to its high copper purity and the Simsbury copper ore at the time was world-renowned for its copper purity so exportation was worth the EFFORT.
In my new book I discuss this in detail and give many research papers to substantiate this information not for the Higley dilemma but the power of LIA.
One of the projects I am looking know is to try to compare and see if Chinese paktong was used in earlier contemporary counterfeits prior to 1830 which seems to be the cut off we discuss in the Gurney book until recent evidence has shown that Matthew Boulton was purchasing and making paktong objects like buttons in and around 1771! From a previous post here via Keith Pinn book on paktong. I have yet to verify a paktong Kleeberg for the earlier date CC2Rs say in and around 1771-1825 which all seem to be European GS so to speak and not Chinese paktong (i.e., lower copper, higher zinc, 1-2% iron) based on Pinn's empirical formulas for these two metals in his fabulous book. This will also IMPACT possibly Larry Schmidt and his Davignon Bust Halves XRF analyses for all his varieties dated prior to 1830 on his website of CC Bust Halves. He like me assumed back-dating on all Bust Halves CCs with a date earlier than 1830 to being produced 1803-onward. We really can't say that anymore withis new evidence about Boulton and verification of ships bringing in paktong metal into England in and around the 1770's. Its a whole new ballgame on this so-called 1830 cut-off date Oliver Hoover and everyone at the ANS was so adamant about ...
Upward and onward ... everybody.
LOL.
JPL
Edited by colonialjohn
02/01/2017 8:09 pm
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Pillar of the Community
United States
1156 Posts |
It is safe to assume that the type of XRF devices used in jewelry stores, pawn shops and perhaps the TPGs are not sufficiently sensitive to detect gold in pre-1850s regal Mexican silver coins?
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Pillar of the Community
United States
1757 Posts |
Probably not. For this to be certain I would like the instrument detection limit down to 0.01% with an accuracy to 0.1%. Those XRF guns (newer models) may have this accuracy to 0.1% and IDLs of 0.01% or better. Case by case basis. Remember also there are other indicators like the required presence or more importantly the LEVELS of lead, good level of copper and silver, the presence of questionable elements like iron ,nickel,zinc, etc.. Most debasement of Portrait China Type II's of course will be PREDOMINATELY with copper only and zinc and tin really enter predominately with the Class I's. Personally, I have yet to verify the purity of silver on electrodeposited type Cap and Rays being theoretically near 98-99%. Bob is working with a state of the art laboratory I am sure he will substantiate this fact. In terms of this specimen here notice how we must use numismatic knowledge and scientific analysis to prove our facts. Based on the analysis his piece was confirmed as a debased copper Cap and Ray. The instrument was probably not sensitive enough and time demands did not allow say a surface SEARCH of 6-8 surface spot analysis on the coin. Besides with this specimen I do not think we are entertaining the idea of a modern forgery or a silver electrodeposited Cap and Ray. Will be clearer after Bob releases his second book. You will also get a real good taste of many different alloys that go into a CC after my book is released in a few months. Be patient.
Edited by colonialjohn
02/02/2017 4:08 pm
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Pillar of the Community
United States
5362 Posts |
jgenn You ask: Quote:
It is safe to assume that the type of XRF devices used in jewelry stores, pawn shops and perhaps the TPGs are not sufficiently sensitive to detect gold in pre-1850s regal Mexican silver coins? Unfortunately the answer is yes in most all cases. However, do not despair. The Handheld XRF is of great value in all but a handful of cases. The need to isolate the trace of gold is critical only for the class of Portrait 8 Reales that were made for the China trade in the US and other countries after about 1870. These coins contain 90% silver. They are not typical counterfeits that contain little or no silver. These coins produced decades after the originals were made require a laboratory facility that is up to date. I use a Laboratory with a new generation XRF that can detect accurately to 1 ppm all elements between Carbon and Uranium on the periodic table of elements. This type of testing is costly and should be done only when it is absolutely needed. Typically I need to come up with $500 to have access to the machine for 1 hour. To get the 1 ppm level you would get 3 tests at most for $500. At the 20 ppm level you get 6. At 100 ppm you can get 20-30. This is done by doing shorter interval testing which makes the results less precise. Consider that 1 ppm testing is accurate to 0.000001 or a percentage of 0.0001%. That is one ten-thousandth of one percent. Just 10 years ago that standard was unobtainable. The instrument John has is accurate to about 0.01% which is fantastic in the majority of cases. This is about as accurate as the 100 ppm tests the lab can process at 20-20 per hour. This level is still more accurate than you need in 99.9% of cases. In most cases, a handheld XRF accurate to 0.1% will be good enough. It is perfect if the question is "How much silver is in this coin?" and you can get them for $5 each. Most counterfeits were produced in off metals and for all of these 0.1% is more than you need. This covers contemporary counterfeits and numismatic forgeries. The test is so cheap that the TPGs have finally begun to use them in some but not all cases. In my new book, I will be using both types of lab tests but far fewer of the detailed expensive tests than the handheld XRF type. The difference between $5 and $250 is too significant for my level of income.
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Pillar of the Community
United States
4883 Posts |
Since my original post, this thread has proven to be a bit of a revelatory odyssey for me. Below I've listed the main points I'm taking away from this discussion.
First, not all counterfeits from this time frame bearing a Zs mint mark are of the sort catalogued by Riddell, that is, struck with identifiably phony dies on heavily debased planchets. Some, whether their origin was within the mint or outside of it, were struck with official dies and only marginally deficient in their silver content.
Second, for the latter very deceptive forgeries, either determining a specific gravity or doing an analysis by xray fluorescence should pick them out. That said, many certainly circulated undetected for a long time, and probably wouldn't necessarily be recognized as spurious by many numismatic dealers, even those specializing in the type.
Third, XRF testing ought to continue to show that these didn't contain the sorts of metals that the cruder forgeries might be expected to. They're simply mildly debased (my initial speculation that some Pb might be present can be safely dismissed, I think).
Finally, in a gerneral sense this has served as a reminder that evaluating coins in isolation can lead to wrong conclusions. I originally was looking at the "3" in the 1832 specimen as a possible overstrike until the 1833's gave context to that, revealing instead that there was a distinctive, irregular formaion of that numeral.
Colligo ergo sum
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Pillar of the Community
United States
5362 Posts |
Lucky Cuss That is a great summation and if we helped you learn that great. Now we need to convince the rest of the old school dealers that simple science can work to the benefit in the long run.
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Pillar of the Community
United States
3229 Posts |
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Pillar of the Community
United States
4883 Posts |
A few days ago, a nationally known numismatist with whom I do business showed me another 1833 Zs he'd just acquired as past of a larger group of 8R's (these being really not within his field of expertise). The specimen exhibited the characteristic "barred" 3's pictured above. Weight was right at 27 grams, and I judged it to be VF. Its appearance was a bit "funky" but my impression was that this might be due to its being yet another example struck with genuine dies but debased in composition to some degree.
Even with his evaluating it as having been cleaned, he was pricing it at $100, which I thought too dear for what now seems to me to be an awfully common First Republic issue.
Colligo ergo sum
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Valued Member
United States
426 Posts |
I have a couple debased Zacatecas 8R's myself a 1833 and 1835 and from many others that I have seen it seems the green verdigris is more common on debased issues. I have always attributed it to a higher percentage of copper present.
The early to mid 1830's were very turbulent times in Zacatecas culminating with a full blown rebellion that had to be put down by the central government so I don't doubt that there was rampant corruption at the mint.
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Pillar of the Community
United States
5362 Posts |
I have also noticed the number of 1833, 1834 and 1835 Zs coins that are debased. They are also connected with very worn and/or damaged dies in many cases. I wonder if it is a second case of undefaced worn dies being sold as scrap metal. In 1835 many of the debased examples have a reversed rim design with one die in the mill being mounted backwards. If this correlation proves to be accurate then the "error" of reversing the dies may just be a way for the forgers to identify their own work so that they could refuse to take them.
I think it is a topic that remains open with no fixed answer. The debased coins were fraudulent whether they were made in the mint or outside it. They are similar to the 1833-1839 Go debased coins and the 1829 Ga copper center coins. Definitely bad (debased) but struck with apparently genuine dies.
Only the 1832, 34 and 1836 Do coins are attributed solely to outside forgers by most experts. It is a topic I plan to explore more in my new book on Cap and Ray 8R counterfeits.
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Pillar of the Community
Czech Republic
803 Posts |
Swamperbob said: "First of all the 3 punch used at the mint had the bar I see here. It connects the point at the end of the loop with the point at the center of the 3. There are no overdates shown here."
That's it right there. I don't see any overdates, as well.
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Pillar of the Community
United States
5362 Posts |
The 3 punch with the bar is clearly a match for the one used at the mint. That establishes that the working dies were originally made in the mint shop or were at least made with a genuine 3 punch. It does not establish where the coin was actually struck.
One theory advanced was that when the mint changed hands in 1836 from the State of Zacatecas to the central government of Mexico - that the die tools (punches used to make the dies) were sold off. The 3 illustrated in "Resplandores" for the 1836 8R is the new 3 variety associated with the new die style.
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Posted 02/01/2017 10:40 am
