Hi all... can the Sigma Basic (or Pro) Model Tester analyze Lincoln and IH Cents? The documentation mentions the ability to check copper, but it doesn't list US Cents anywhere. I also saw that custom parameters can be uploaded to the PMV, so has anyone added a profile to a PMV to test Cents (if it doesn't already come with that profile)? Thanks!
Sigma makes the Precious Metal Verifier (PMV) that's been discussed in a number of other threads on this site. There is a basic and a pro model and they analyze the properties of coins and bars to see if they are legitimate and not counterfeit. The device is programmed with the specific properties on different coins and can help determine if they are authentic. These have become very popular (there is a waiting list for several months to get one). It's not the end-all-be-all test, but it's a really good one. With a single 10oz bar selling for about $300, it would only take a few bad bars to make back the purchase price... not to mention the number of fake Morgans that seem to be getting harder and harder to detect.
I'm not sure what the point would be, given that genuine cent bronze is so very inexpensive. I don't think there's a big problem with otherwise-convincing fake cents being struck on the wrong metal.
As a collector of cents, I’m seeing more and more fakes showing up, especially for key dates and even semi-key dates. Gone are the days when a magnet would help or that they were obviously cast. The newest fakes are actually being make with a die, at perfect weight. so, while the base metals may be cheap, getting the alloy perfect still seems to be a problem for the counterfeiters. That’s where a PMV might be able to help and why I was curious.
If you can do minor science, this unit works for me when I need it, but it isn't beep and read https://www.amazon.com/Signstek-Digital-Ultrasonic-Thickness-1-2-225mm/dp/B071YN23T1/ google this "detect metal composition of coins with ultrasonics"
Copper is not a precious metal. If you put a nice pure copper medal on a Sigma PMV and have it scan for .999 silver, it will hit right between the goal posts.
Huh. In their shoes, I'd be melting actual cents to get the alloy. In any event, if the alloy is wrong, it might or might not make a difference in the PMV reading. I'd recommend finding someone who has a unit, taking some known fakes and known good coins, and seeing what the unit has to say about them. I wouldn't get my hopes up, but then, I'm a big Sigma skeptic to begin with. An XRF gun would be more informative, but you'd need to catch a LOT of fakes to make it pay for its five-figure price.
There was a great movie (I can't remember the name) where an art forger was melting antique toy soldiers from the 17 through 19th centuries and mixing paint pigments in with those melted metals. It fooled all of the X-Ray and chromatographs that people because all readings showed up with the properties on old metal. I'm not a metallurgist, but I believe melting actual cents would separate the metals. Otherwise, counterfeiters will be doing the same with other coins. They would be melting a cull Morgan (for less than $20) and re-strike it into an 1895 Morgan with 100x. Wouldn't they? Then the Sigma tests would all be thwarted. Nonetheless, I know there are lots of Sigma skeptics, so I appreciate the input. I'll try it on a Sigma unit and see what happens. I wish I could afford a $15k XFR gun!
The sigma machine measures the resistivity of the metal and compares it to a standard for the alloy. Indian (beginning midway through 1864) and Lincoln cents are 95% copper 5% tin and zinc. Since the ratio of tin and zinc can vary, the actual alloy can vary. You need to know if a variable tin/zinc ratio changes the resistivity to the point where Sigma can't develop a standard baseline. Or maybe, there are no detectable differences A couple other things to consider What kind of planchet will be used for a counterfeit? 100% copper is easily available. Is there detectable resistivity difference between 95% Cu and 100% Cu. Assuming Sigma can develop a baseline standard, will they be able to tell the difference? I wouldn't worry about alloys with more Sn and Zn, since you'll start seeing color change Laminations are known to occur in Cooper cents, and that will affect the resistivity "Woody" cents (improperly mixed alloys) may generate false readings I'm not a metallurgist, and don't know if any of these are significant, but any/all of them could be a reason why Sigma doesn't offer a setting for copper cents. I recall reading in their literature that their equipment may give false readings on early US coinage due to allowing methods used at the time (don't hold me to that as I'm going from memory)
Not as I understand it. The microstructure of alloys depends heavily on how they're cooled and worked, but when you melt the metal, it all becomes a uniform solution. Ah, but they do that, and have been for a long time. From what I've read, counterfeiters overseas were melting common pre-1933 US gold and striking it into counterfeits with perfect composition, but in more desirable series, dates, or grades. Who wouldn't trade three circulated eagles for ten freshly-struck $3 coins, or even thirty $1 golds? I've seen some of the online fake wholesalers list Morgans both in silver-plated copper/brass and 90% silver. A Sigma tester, or even an XRF gun, would be no help against the latter.
You could try it, but the resulting alloy will be high in copper and short on zinc. Zinc has a much lower melting point than copper, in fact it boils at a lower temperature than copper melts. So as the cents melt some percentage of the zinc will boil off. trying to get an exact percentage composition with bronze or brass is not easy. You have to use a surplus of zinc because part of it will boil off in the melting and pouring of the metal. Timing can also be critical because the longer you hold the melt molten the more zinc is lost.
But brass, once it's made, melts at a lower point than pure copper. Yes, zinc is volatile and you'll lose some; even below its boiling point, its vapor pressure is high enough that some of it will come off. (Like water, it doesn't have to boil to evaporate.) But it's slower to do that when it's already alloyed, and it should be possible to add zinc (or zinc-rich bronze) to make up the difference. Or, you could get a bunch of real cents, pound them flat in a collar, and re-strike them. Or, more likely, contract with a foundry to give you sheets of alloy with the proper spec.
Thanks for the help and education. So interesting. I had no ida zinc has a lower melting point than copper, but it makes perfect sense that not all metals melt the same. I also had no idea that the fakers were already taking existing lower-value coins and melting and striking them into higher-value ones. I'm a low-level hobbyist collector, and every now and then, I do buy raw coins, which sounds like that's a bigger and bigger gamble as time goes on and fake get better. Ugh. I did read on another thread on this forum that fakes that get past the TPGs can even have a high value.
That's true, but it melting point is still above the boiling point for zinc. Or just buy some blank planchets from an error dealer. they are common enough to get in bulk.
