FORVM`s Classical Numismatics Discussion Board
Numismatic and History Discussion Forums => Greek Coins Discussion Forum => Topic started by: Virgil H on January 26, 2023, 10:53:39 pm
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I have had this coin a long time and I have no reason to doubt it. I was looking at it, taking photos for my gallery and decided to look it up on Pella. Mine is AR 28mm-29mm, so a larger size on the range, but mine is only 14.4 grams. Weight is on low side. The range in Pella is 15.08 grams to just over 17 grams. I just wanted to check here to see what you think. This is Price P186. Babylon mint. Maybe the test cut has an impact here, but that cut isn't huge. I have also seen wide weight variations in other coins, so just wanted some other opinions.
Thanks,
Virgil
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Could it be a fourrée?
On the reverse you have this black hole in the middle and some damages near the edge at about five and six o'clock looking as if some parts of a plating had detached there.
Regards
Altamura
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Hmm, I never thought of that. I have no experience with fourees, so I don't know. It isn't super obvious to me if it is. That spot on the back is definitely something I have wondered about. Also, this coin is also, to me, a bit unnatural looking, but I have no other silver coins that size and with the relief this one has. The photo doesn't really convey that. It is a pretty coin. I just am not sure how to tell if it is plated, if it is, that has held up well over the centuries, assuming it is actually ancient. Honestly, this is one coin I have always thought might look to good to be true. But, like I said, I have no experience with coins this size with this level of detail. I realize I haven't said very much here. This is a coin I have looked at a lot and wondered about. And I have nothing I can compare it to in my collection. LOL.
Thanks,
Virgil
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If this is a fourree (that would explain weight and some details on reverse), I would suspect the obverse test cut was one of the "fake test cuts" placed there by the forgers before it was plated. (Of course, it is possible for a test cut to fail to break the plating.) I know the phenomenon of "fake test cuts" is well documented for Athens tetradrachms:
(https://www.acsearch.info/media/images/archive/30/10036/10334854.m.jpg) From CNG [acs Link] (https://www.acsearch.info/search.html?id=10334854)
But I've never seen it on an Alexander/Philip III tetradrachm. That would be a really cool discovery, in my opinion.
The question for me: did the forgers cut the cores manually, then plate them, or was the cut actually part of the original die (which would be technically quite impressive!). I'm having trouble finding them with keyword searches, but i had the impression that I'd seen a couple of the owls that looked similar enough to be from the same dies, but I could be imagining that part....
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Curtis,
Those are some interesting comments, I had never thought of test cuts being part of a forgery. I think this coin might be one that someone needs to see in person. I am going to look at it under the microscope and see if I can see anything else. Thanks.
Virgil
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So, I have had a chance to look at this one under the microscope. One thing I will say upfront, based on what I have seen of weight ranges, this one isn't that far off. That said:
The observe test cut has no signs of their being a base metal underneath. If this is a fouree, this cut was done before plating.
On the reverse, I looked at the "hole" in the center of the back and the spots on the edges. Based on what I know, they certainly look like flaking plating. I will say this is pretty thick silver plate, but those areas on the reverse are pretty damning.
I never saw this coming. I will say that the only other "fake" I have bought (not counting the tourist fake I bought in Ghazni, Afghanistan, in the middle of a war) was from this same dealer where I ended up with a contemporary imitation of an Ephesus coin. So, that tells me this dealer is not overly attentive.
I have no idea, but I am glad I posted it here. The more I look, the more I think it is a fouree.
Thanks to those who have commented on this coin.
Cheers,
Virgil
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Depending how it fit into your collection, the price, etc., I can see that being a disappointment.
If it was an ordinary fourrée I'd feel that same way. Personally, though, I would think that false test cut makes this quite a special and interesting coin. (But I find fourrées quite interesting. I'd be going down a rabbit hole trying to figure out how special.)
I wonder how many of these fake cuts are even known on Hellenistic fourrées? I don't recall seeing any after 454-404 BCE owls.... If you set out to buy one, you'd have to look for a long time or get lucky (though I've seen a couple owls recently; lost on both; I think there was a premium for the false cut).
Apparently the ancients knew about this phenomenon, since someone punched the back later. (Raises another interesting question: how long did most fourrées circulate before being caught? How many were never caught? They're often surprisingly worn.) It still worked on your dealer!
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Looking online, I saw one example said to be 'very crystalized', which weighed around fifteen and a half grams. I suppose a tetradrachm on the 17 gram standard could be reduced to the weight of your coin by 'crystallization'. Maybe a jeweler with an XRF gun could shoot the areas of 'broken plating' on your coin and see what it shows.
I might rather have an ancient fouree than a badly crystalized genuine coin (depending on how rare the coin).
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Thank you all for your comments, especially Curtis and Kevin's last comments. I am not overly upset, it just puts the coin in a different light for me. The intentional test cut is super intriguing. So, I am not upset. I wasn't upset with the Ephesus coin, either. An ancient forgery is an entirely different thing for me than a modern forgery. I think I have always suspected this tetradrachm was a bit off. I am not familiar with the jeweler's XRF gun and will look into that. This coin was not overly expensive, so no real worries on that and this could make this coin more valuable, perhaps.
An interesting item for my collection so I am fine with it if this is a fouree. I am going to go to the big jeweler in town (that I have bought jewelry from) and see if they will look at it for me.
Thanks again, mysteries are fun.
Virgil
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XRF guns are all prohibitively expensive for me, otherwise I would have bought one long ago. I think even most jewelers and people who buy and sell gold and silver do not have an XRF gun, but I know some do.
An XRF reading might be of corrosion products, if they are present, versus a straight reading of silver or copper/bronze, but this could still give a good indication of the coin's metal/alloy.
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It would be interesting to know whether an XRF gun could make anything of a fourree. They generally don't penetrate very deeply at all, so you would have to try to aim it at the break in the plating. I've never seen one in action but I've spoken to people who have used them on coins and, like everybody, read what's readily available online.
I don't know if he still does it, but I believe Rasiel Suarez was offering XRF as a commercial service (but it's not super cheap, since the guns are outrageously expensive, and I think each use is costly because they wear out).
I actually have three coins that have been subjected to XRF testing (all before I was owner), and I really enjoy knowing the results.
One is a Byzantine Solidus that Ras had tested with his own XRF gun (it was actually the cover coin from ERIC II -- here in my Forum Gallery [LINK] (https://www.forumancientcoins.com/gallery/displayimage.php?pid=174582)). From what I understand, the surface alloy of ancient gold coins is pretty consistent with the core, but the XRF gun is only measuring the few nanometers at the surface (98.5% AV).
The other two were from the group that Harlan Berk sold after Jyrki Muona had allowed them to be analyzed for Kevin Butcher & Matt Ponting's big study of the Metallurgy of Roman Silver Coinage, from the Reform of Nero to the Reforms of Trajan (Google Books has a substantial preview [LINK] (https://www.google.com/books/edition/The_Metallurgy_of_Roman_Silver_Coinage/f_EKCgAAQBAJ) and several of their articles, incl. some with Muona, are available free online). One of them -- an Otho denarius -- is also in my FAC Gallery: [LINK] (https://www.forumancientcoins.com/gallery/displayimage.php?pid=174650).
A big contribution of Butcher & Ponting's research was to show how different the results of surface XRF are from the interior of the coin -- at least for silver coins. (Hence the coins were drilled and "quartered" to check their insides.) (jmuona had posted at least one of those two in his gallery here.)
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I meant to suggest checking the areas of the coin in question where there might be platting breaks. It might only be reading corrosion products, but these are different between copper/bronze and silver...maybe not good for ascertaining the exact alloy percentages, but maybe good enough to identify a fourree.
Edit:
Previous claims of accurate XRF readings through coin slabs appear to have been disproved.
https://britnumsoc.files.wordpress.com/2022/07/269-xrf-slabs-oddie-blog-001.pdf
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In the olden days, before digital scales, it was possible to do a specific gravity test on a coin using a balance-type scale.
It is certainly cheaper than an XRF gun or paying someone to do an XRF test for you.
The results might not be as accurate, but they'd likely tell you if there was reason to be concerned about your coin.
As I recall, here are the steps:
1. Weigh the coin.
2. Weight the coin suspended in water using a piece of thread to suspend the coin. Use distilled water if possible, but regular tap water works too.
3. Subtract the weight of the coin suspended in water (step 2) from the original weight of the coin (step 1).
4. Divide the number in step 1 by the number gotten in step 3.
The specific gravity of pure silver is 10.49.
Any number substantially lower would indicate a significant amount of base metal ( such as copper); any number substantially higher might indicate presence of a denser metal such as lead or gold.
I'm sure there are videos online how to do this -- maybe even using a digital scale.
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Thank you all, Especially Callimachus, Kevin, and Curtis,
This has become quite the item of interest for me, even though it isn't a very expensive or valuable coin, but I truly like to know what I have and this has been a learning experience. That is worth exploring this if for no other reason. My first step is contacting the top jewelry store in my area to see if they have an XRF gun. Chances are they do, they are one of the major non-huge city jewelry stores in the country, partly due to their proximity to Augusta National and they have developed an international clientele over the years, including golfers who go there every year, not to mention Masters patrons. I have shopped there and they are pretty amazing. Plus, it is almost Valentines Day, so what better place to go. LOL
Virgil
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It might be a challenge to get an accurate understanding of the XRF results. This might be because of what is on the surface of the coin, but also might be because the person analyzing the results is not familiar with what you are looking for. Myself, I have no experience testing with XRF, so I don't want to oversell what I have been writing here. I probably know enough to be dangerous. If the XRF of the 'broken plating' areas on the coin reads 'copper or bronze', it might indicate a fourree (or a large inclusion or unmixed particle of copper or bronze). If it reads corrosion products of copper or bronze it might indicate a fourree, or possibly just copper or bronze that has precipitated out of a solid silver core over the centuries and now lies on the surface. If the XRF reads silver chloride, perhaps it would mean that evidence for a fourree has not yet been found.
It seems like something worth doing in any event, as it will hopefully be a learning experience. Please let us know the results if you succeed in getting the coin tested.
Edit - addition:
https://www.getty.edu/publications/artistryinbronze/conservation-and-analysis/46-kantarelou/
I thought you would enjoy the above linked report. The XRF device used is portable, but looks to be more substantial than an XRF gun. I note that the focused area of testing can be quite small, so the areas of 'broken plating' on our coin in question look to be large enough for testing. The authors report the ability to calculate the original metal composition from the XRF results of corrosion products. Perhaps this would be beyond the ability of most jewelers.
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In the olden days, before digital scales, it was possible to do a specific gravity test on a coin using a balance-type scale.
I was also thinking about a SG test, but I'm not sure of testing for silver and copper/bronze. I have not yet ever tried to do a SG test myself.
Below, I am citing and quoting the work of two people who I believe are well-regarded on this subject:
Oddy and Hughes ‘The Specific Gravity Method for the Analysis of Gold Coins’ in ‘Methods Of Chemical And Metallurgical Investigation Of Ancient Coinage’
Pages 75-76, “In cases where the specific gravities of the pure metals are fairly similar (e.g. silver and copper), the calibration graph is nearly horizontal and the error in reading off a composition from the measured specific gravity is very great…But where the differences in specific gravity between the pure metals are much greater (e.g. gold and silver, or gold and copper) the calibration curve is steeper and a greater accuracy is possible in the final analytical result. This means, as far as the coinage-metals of antiquity are concerned, that the method is only applicable to gold coinage, and even this statement must be slightly qualified, as will be described below."
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Thanks again for the great responses. The jewelry store responded and said they have such a device and would be happy to look at and test the coin for me. So, I will be going there probably early next week to have that done and probably buy my wife a present for Valentine's Day. As a jewelry store, that place is amazing. I will let you know if I find out anything useful. This coin has entered into my "most intriguing coin" category for now. I will probably bring a couple other coins with me, one with a real test cut, so they can see the difference. If I were a jewelry store tech, I would actually be happy to take a look at an ancient coin like this.
Virgil
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In cases where the specific gravities of the pure metals are fairly similar (e.g. silver and copper), . . .
Really ? ? ?
Specific gravity of copper: 8.95.
Specific gravity of silver: 10.49.
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It is difficult to measure specific gravity of coins. I have a balance and set up to do it but I have not tried it, because, apparently, to be accurate you have use a liquid other than water. I do not remember the details but it was not as simple as using water.
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I understand the concept of specific gravity, but not to the point of doing it with a coin. I also don't have a balance scale. I don't think I will try it with this one, but who knows, maybe I will. I am hoping that the XRF gun will do the trick for this coin. We shall see. My problem (that is maybe a good thing) is when I get on something like this, I really want to know. Part of the fun of collecting.
Virgil
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In cases where the specific gravities of the pure metals are fairly similar (e.g. silver and copper), . . .
Really ? ? ?
Specific gravity of copper: 8.95.
Specific gravity of silver: 10.49.
Apparently yes, those two are too close, according to the aforementioned authors. The Specific gravity of gold is 19.3.
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If this is a fourree (that would explain weight and some details on reverse)...
In round numbers the density difference between copper and silver could account for the difference between 14.4 gm and an 'expected weight in silver' of 17 gm.
A rule of thumb for a 16 gram silver tetradrachm is about 1.5cc (volume) of silver (~10.5 grams/cc). Copper is ~8.9 grams/cc so the weight of 1.5 cc is about 14 gm. It's conceivable, albeit not certain, that most of the coin is copper.
PtolemAE
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Update on this topic. I finally made it to the jewelry store and they examined the coin with their metal analyzer, XRF machine. He looked at the place on the reverse that looked like possible plating having come off. He said the coin is 92% silver, so not a fouree. I haven't looked up silver content of these coins yet, but that seems pretty reasonable for an official coin. I am happy it is not a fouree, but I also would have been OK if it was. That Paphlagonia bull coin I posted about elsewhere is now being made into a necklace for my Taurus wife. I know that isn't a popular thing, but I have two examples of this coin type and I think the necklace will look nice. Thanks again for all the discussion on this coin.
Virgil
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XRF only reads the surface of a coin. It does not tell anything about the core.
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Rarely does the photo color matter for discussion here, but your photo has an overall reddish hue. If it is a fouree, you should be able to see some bit of bronze in the edge cracks or punches. If you don't see any at all, then I would assume it is normal mint issue silver.
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Thanks Mac and Joe for the comments. I asked them to look at the little "black" spot on the reverse that looks like a place the plating came off. I can't say for sure he did that because I didn't watch him. Also, not sure if it makes a difference, I called it an XRF, but they referred to it as a metal analyzer. I guess I assumed they were the same thing. Maybe not. Jewelry stores need to know if things are pure throughout. The owner assisted me along with an associate. He is a coin collector (US gold) himself and very, very elderly. It was interesting to see the dynamic in the store between him and his employees and customers. A true professional and his store is probably the best jewelry store in the Southeast. It was started in 1975 and is right across from the main gate of Augusta National Golf Club, home of the Masters. The place is an institution in Augusta. There are pro golfers who go there every year when in town. The service is just unbelievable no matter what your budget is.
On the color, in hand, it looks more like slightly tarnished silver that I don't think I would call reddish. I am going to look under the microscope again at that spot on the reverse. The edges look all silver. I have very little experience with silver tetradrachms, so I don't have a lot to compare it too. As previously discussed in this thread, the test cut is silver all the way down, hence some speculation it was done prior to plating. When I go back to pick up the necklace, I think I will ask them to specifically look at the "chip" on the reverse and hope I don't insult the guy who did the analysis. For now, I am treating it as an official issue.
Thank you all so much for helping with this.
Virgil
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That still leaves the original concern, the 14.4g weight....
My problem (that is maybe a good thing) is when I get on something like this, I really want to know. Part of the fun of collecting.
No doubt others here are agonizing over the mystery as well! :)
As djmacdo noted, XRF is usually understood to measure only the surface content of the metal. As you say, pointing it directly on the area of suspected broken plating would hopefully work. (Perhaps looking at under magnification? I don't know if it would be reasonable to try to gently clean the areas inside the cracks/punches.)
There was an important series of articles and a major 2014 book showing how dramatically different the surface and core can be, even on solid AR coins, and that XRF fails to measure what's inside a coin.
Butcher & Ponting (Cambridge: 2014), The Metallurgy of Roman Silver Coinage. There's an 87-pg preview on Google Books: https://www.google.com/books/edition/The_Metallurgy_of_Roman_Silver_Coinage/aBVoBgAAQBAJ [LINK (https://www.google.com/books/edition/The_Metallurgy_of_Roman_Silver_Coinage/aBVoBgAAQBAJ)]
Previous studies had used surface XRF (e.g., Walker's 3-Volume The Metrology of the Roman Silver Coinage [1976-1978]) but gave inaccurate results, since the core was different from the surface (sometimes by a lot), and XRF couldn't measure it "from the outside." That is, without drilling into the coin. Which is exactly what Butcher & Ponting did.
(A major contributor to those studies is/was a member here, jmuona, who donated dozens of coins for testing -- many still illustrated in his Forum Gallery. They were returned and sold by Berk a couple years ago. I bought two, both in my galleries: Otho [LINK (https://www.forumancientcoins.com/gallery/displayimage.php?pid=174650)] & Titus [LINK (https://www.forumancientcoins.com/gallery/displayimage.php?pid=181839)].)
If the XRF technology has changed, or jewelers use something else to measure what's in the core, I'm interested in learning. (My uncle is a jeweler, and has even bought the odd ancient coins collection. I routinely bother him with such questions, but he hasn't had any news for me.)
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The plot thickens, as they say. Thanks for the links and info. When I go back I am going to ask some more specific questions to possibly clear some of these questions up. My only point of reference for this with the jeweler is that they could get ripped off with surface only readings, but I am also sure they have other ways of telling if things are real or not. This is not the kind of jeweler that advertises buying gold and silver like some do. I am sure they do it, but that is not close to their core business and that would possibly be "below them" in their position as the highest end jeweler in a many state area, including Atlanta. I am somewhat intimidated in there. They are way out of my league. I don't mean to insult those who do buy this stuff., it just isn't part of their business model. So, who knows? LOL. That said, they are the kind of people who would have tested my coin even if I wasn't making a purchase. The people who saw my coins were interested in seeing them and learning about them.
Thanks all,
Virgil