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Old 12-17-2011, 07:06 PM   #1
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Tools of the trade: Verifying PM authenticity

I thought it would be good to start a thread where members can contribute info pertaining to tools that are useful for verifying PM authenticity.

In particular it would helpful to list info in a format such as:
a) Name of tool.
b) Approximate price.
c) Specific manufacturer/model# that have experience with, if applicable.
d) Additional helpful comments about the specific tool.

Thanks in advance for contributions to this thread!
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Old 12-18-2011, 02:12 AM   #2
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Hands and eyes - priceless.

I would say the most useful tool would be digital scale. They range in size but you can small ones on eBay for like $10-$15. Also as previously discussed rare earth magnets work great for silver, and they are inexpensive. I got some at Radio Shack for a couple of dollars. For the specific gravity test you can use string, a glass of water, and the previously mentioned digital scale. Nothing fancy here.
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Old 12-18-2011, 05:16 AM   #3
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Things I have used:

- Digital scale! make sure it's precise to a fraction of a gram, preferably 0.01g or better
- Coin volume vs weight. a simple diameter/thickness calculation is good enough when you're trying to establish 18ct or 9ct 'medallion' type coins from 22ct bullion - helpful when you are working with unusual coins. You can also use displacement in liquid but don't use water. Use something with a low surface tension like spirit. This won't help with well executed bullion fakes though.
- Rolling a few coins between hands helps distinguish gold and silver from other metals, by ear. When you've handled a lot of precious metals, it's possible to tell when the coin isn't one of those. Silver in particular has a highly distinctive timbre. This may even work for tungsten, although I can't confirm! I recommend you get very familiar with this method - handle coins frequently.
- Acid, although don't go near this unless you know exactly what you are doing. HCL and HNO3 can both cause burns to the lungs from fumes at room temp. They are gasses, held in liquid and constantly evaporate. You'll feel like you have cold/flu later, but it is in fact edema caused by the acid. Not fun.
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Old 12-18-2011, 09:09 AM   #4
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#1 Best Selling Digital Caliper on Amazon:



Portable digital scale that measures to .01 grams (rated only to 100 grams, so not good for 10ozt bars/coins, but perfect for 1ozt or smaller):



2" long Rare Earth Magnet (keep away from your credit cards!):


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Old 12-18-2011, 12:52 PM   #5
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I have an El Cheapo digital scale that I picked up from the coin shop for $15.

The only other "test" I currently "do" is to put the Gold & Silver Eagles into the US Mint plastic tubes for stacking. That takes are of the Outer Diameter measurement and pretty much the Thickness measurement (20 coins fit in there pretty well).

APMEX sells slightly used Mint tubes for $5.00 each I believe. I get mine by asking either of the coin shops I patronize if they will give me one...

I like h4rdware's suggestion to handle your coins often. The coin dealer told me once that he can "just tell" because he has handled them SO MUCH.

*** If anyone can tell us how to get one of those (legendary?) Chinese tungsten slugs about the size and shape of a 1 oz Eagle or any other common 1 oz gold coin, that would very useful (for seeing how it "rings" when dropped, if it "feels" different, etc.). ***
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Old 12-18-2011, 02:20 PM   #6
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I want to preface this reply with "I'm sincerely not trying to be a douchebag with this post".

That said, the nature of what it is that I do for a living requires my firm to own an XRF. This instrument can definitively determine not only if your metal is gold or silver, it can define purity to parts per million. This is a very expensive instrument, and is regulated by the NRC as a result of the nuclear material contained in the sensor tube. Every single commercial scrap yard and processing facility owns one, and they use it every single day. This instrument is invaluable to them in the identification of many different alloys. They will tell you the most tested metal is stainless steel.

Back during boom times, our girl at TMR, Penney, told me they could peel off as much as forty percent because the wreckers who scrapped big volumes of material never bothered to hang around to have their loads checked out, and as a result, lost out on an upgrade in the material after being clipped. Surprisingly, older stainless steel contained significantly more nickel than modern stainless, as a result of technology and updated alloying technologies. Penney told me that sometimes, a load would come in presumed to be 304 but turned out to be 316.

It is possible to take suspect rounds or bars to a scrap dealer and have them shot for a very nominal fee. If you had something like a dozen tubes of silver rounds, and the tubes were homogeneous among themselves, in other words, if each tube contained twenty identical rounds, you could just do a "dip test" on each tube. Perhaps one or two samples could qualify the tube.

Anyhow, XRF remains the surest method short of FAAS, of Flame Atomic Absorbtion Spectrometry. An interesting paper on this method can be found here:

http://proj3.sinica.edu.tw/~chem/ser...1256028899.pdf

We use this analytical method to test samples of building materials and coatings systems for heavy metals [RCRA metals]

The cheapest method to test silver/gold is still the water column.
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Last edited by ancona; 12-18-2011 at 02:37 PM.
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Old 12-18-2011, 02:30 PM   #7
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ancona - heh, I bet DCFusor is digging around in boxes for potential XRF scanner parts right now!
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Old 12-18-2011, 02:36 PM   #8
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I have no doubt he can build one either. Have you been to his site? It's like a whole other language.
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Old 12-18-2011, 03:36 PM   #9
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(blushing)
I probably could build one if I wanted one bad enough, have to do a little work on seeing how they're doing it now. For me, I'd just expose my pm's to some neutrons from the fusion, then look at the resulting gammas on a gamma spectrometer I have (that way I don't have to build anything at all). Not as good as full XRF probably, but probably good enough with the other tests.

I'll have to look into it. Fluorescence implies (usually) that you start with real high energy X rays, and see what comes back. Real high energy X rays aren't that fun to be around...and hard to shield against.

For example, it's real easy to take real high energy light (UV) and get something to fluoresce red at a lower energy (day glo), but going the other way is really rare.

I should note that my partner recently got screwed on an XRF system off alibaba, the guy took the money but then disappeared.
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Old 12-18-2011, 04:43 PM   #10
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I definitely think DCF could build one. That's a shining example of a person who builds bigger scarier devices than I do, which is really saying something...



(a tiny ionized cloud produced at the focal point of a homebrew multi-megawatt laser)
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Old 12-18-2011, 06:30 PM   #11
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OK, I'll bite, what type laser is that you're using? I have a Nd:YAG one here that makes 60j output for 1500j in (big honking capacitors -very scary). It'll punch a hole in a quarter, but it scares me too much to run it often (and it's a PITA, water cooled and all). Looks like you're blasting some foil there?

Anyway, here's a link on XRF stuff.
http://en.wikipedia.org/wiki/X-ray_fluorescence

I perceive that there's a big difference between the affordable (under $10k) ones in scrap yards and the performance often quoted for XRF which has to be the for the very best ones that need things like cryo cooling for the detector and a really nasty-hot X ray source.

As in, the car land speed record is over mach 1. And here's a car I can sell you for $40k that's real fast (my old 2010 camaro SS that hit 200). Not quite the same...All you're saying with XRF is "I have a car". There's quite a range of available performance out there.

I have a gamma spectroscopy setup here:
http://www.coultersmithing.com/forum...php?f=11&t=337

We really got lucky to score that gallon jug NaI:Tl head for about $550, they normally go for a few $k (sometimes a few is a 2 digit number), and this one might not have enough resolution to really do XRF without some extra effort, or more brains in the interpretation of the results. I'll have to look at the problem more.

Anybody got some adulterated gold/silver they want to let me use as samples? I've got pure stuff already (5 9's, lab stuff). Having just chucked a SO, I don't even have any low grade jewelry around at the moment...she got all that.

Looks like the pros add an X ray prism and some mechanicals to get to better resolution, which can be cheap (f you can score a big single xtal of LiF or something), but it's getting complex to eliminate scatter off junk and other issues. Smaller NaI heads are cheaper, and might be good enough at the lower XRF scatter energies, dunno till I look into it more.

The reason these are regulated is they need a pretty hot X ray source, and those are regulated pretty hard out there - even very hard to find surplus and buy without being a radiologist. Evidently scientists don't count, only doctors. You have to go though considerable red tape to get "approved" for that kind of thing.

Most of what I do - I try fairly hard to make not-scary. But not all, and it depends on what you think is scary, too. Some people are freaked out by the fusor, since it does make some radiation but I don't allow any big doses to happen. All the high voltages on that are very carefully screened from possible human contact...
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Old 12-18-2011, 07:26 PM   #12
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I bought one of these:

http://i-c-g.pl/index.html (much cheaper than the more familiar brand)

and also, try this video for testing silver bars with a magnet:


cheers
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Old 12-18-2011, 07:46 PM   #13
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This works by the magnet moving generating current in the bar - and silver is a very good conductor, so it shorts out those currents. That creates a magnetic field that reacts back on the magnet, inside the silver. This is good as he says for silver vs lead (which most could tell with a fingernail hardness test most of the time). But try it with pure copper too - there's not a lot of difference, and you can add a lot of copper to silver before it looks much different, or as he mentions, make it hollow with lead in it (only the surface to small depth matters here). So it's a good test kind of - but there are caveats. It might take some skill to tell between silver and sterling...

It's fun for sure, anyway. I keep a copper and aluminum set of pipes and some magnets around to show kids, they love the demo.
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Old 12-19-2011, 04:16 AM   #14
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<making considerable effort to resist offtopic, while biting DCF's bites>

DCF - that's a small q-switched ruby laser attacking a razor blade. It easily makes holes without the q-switch, but the electric blue flash is replaced by dancing orange sparks. I did have a 30J monster for some years but my wife made me get rid of it - the power supply was larger than our storage freezer and the detailing made it look like a prop from Star Trek.


Sorry PMBug - I'll repair the OT damage later, I have a couple of proper articles in my head which I'm hoping to write up very soon!
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Old 12-20-2011, 07:46 PM   #15
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Maybe not quite as offtopic - if you can get that electric blue flash, you're getting the arc spectrum of what you ablated there (from the big E field) - and that could be used in an optical spectrum analyzer to measure PM purity...same as a flame spectrum, almost - different lines dominate in an arc spectrum. Hmmm....lots of ways to skin a cat.
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Old 04-20-2013, 07:39 AM   #16
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This looks interesting (I have not tried it personally):


It's an app for Andriod smart phones to test the sound/resonance of coins using your phone's microphone.
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Old 04-20-2013, 07:42 AM   #17
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I think I've posted a goldmoney video before somewhere about ultrasound testing with GE equipment:

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Old 04-20-2013, 08:31 AM   #18
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Yes, we had a separate discussion where that was discussed in some detail: http://www.pmbug.com/forum/f13/ultra...s-gauges-1623/

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