Ultrasound Testing fullproof?

Discussion in 'Bullion Investing' started by bullibags, Nov 12, 2015.

  1. bullibags

    bullibags New Member

    Hey Guys so an ultrasound thickness tester can tell you if your gold bar is solid and not filled with something else for example tunsten. Now gold has a speed of sound of 3240 m/s. but what about 14k or 18k does anyone know is it very negligable? if so wouldn't that mean that part of the bar could be 24k and the center 18k and give you a similar read, hence you losing money?
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  3. desertgem

    desertgem MODERATOR Senior Errer Collecktor Moderator

  4. Brett_in_Sacto

    Brett_in_Sacto Well-Known Member

    There are some (very expensive) XRF devices that can immediately tell what is in the metals.

    Example: http://www.ebay.com/itm/SPECTRO-XSO...ometer-MICRO-3MM-SPOT-SIZE-GOLD-/311417445361

    I brought a bunch of mish-mash melted down silver to a guy that had one. He was able to sample big chunks (1-2 inches thick) and tell me the exact amount of silver in each. We also found that they were 62% silver, 1.8% platinum and 2.3% gold - so I scored when I sold him the scrap. (I gotta believe this was some sort of industrial or dental metal?)

    I paid $80 for almost 3 pounds of the stuff in a glass jar at a GSA auction. People thought I was nuts for buying melted slag and lead. It was labeled silver, and none of the pieces stuck to a magnet - so I gambled. I ended up selling the jar for $600 when all was said and done.

    The XRF gun was able to identify each piece and show the variance in the metal content. Some shows more, some showed less - so it was obviously a failed smelt at some point.

    VERY accurate. I want one, but it would cost me more than I'd ever be able to recover by using it.
  5. ToughCOINS

    ToughCOINS Dealer Member Moderator

    @ Bullibags . . . Be careful with your assumptions . . . yes, an ultrasonic tester will differentiate between gold and tungsten of the same geometry. That is because the tester is measuring the fundamental natural frequency of vibration of the tested piece of metal (a function of both mass and stiffness). The test is beneficial for non-destructive testing for tungsten because the densities of tungsten and gold are virtually identical, but their stiffnesses are not.

    This test method cannot necessarily be relied upon to identify other combinations of metals intended to mimic the density of gold however, as metals both heavier and lighter than gold could conceivably be sandwiched together to produce the desired result. With time and inclination, I'm pretty certain a very deceptive gold-plated sandwich metal could be developed. To detect that, a different test may become necessary.
  6. desertgem

    desertgem MODERATOR Senior Errer Collecktor Moderator

    XRF spectrometers are limited in the depth of sample they can accurately analyze. Depending on density, the depth many be in micrometers, up to 50+millimeters in soft minerals such as coal. That is why the wavelength device was used to analyze the 1000 oz gold bars such as in storage instead of XRF.
  7. Brett_in_Sacto

    Brett_in_Sacto Well-Known Member

    Very good to know. I was considering buying one "someday" as I move farther away from my real job and into hobby/semi-retirement. Learn learn learn!
  8. tortoise62

    tortoise62 New Member

    I stumbled across an ultrasound tester which seems to be affordable. The problems is with gold American Eagles - they aren't 24K gold. They are 91.67% Ag 3% Ag and 5.33% Cu. While this mixture was created for durability, it reduces anti-counterfeiting via ultrasound. The U.S. Mint is doing nothing to thwart Chinese counterfeiters. https://fisherpreciousmetals.com/us-mint-on-anti-counterfeiting/

    Canada has Bullion DNA -
    Although damage to the coin can prevent authentication, at least it's something. It's good for gold dated 2014 and newer; silver 2015 and newer.

    Sounds like China will make a ton of cash pumping out gold plated tungsten fakes. Watch how this silver bar tricked XRF testing:
  9. derek819

    derek819 New Member

    Ultrasound testers are very expensive, I have one of these precious metal testers and its absolutely reliable while way cheaper
  10. fretboard

    fretboard Defender of Old Coinage!

    Ultrasonic testers are garbage but the XRF hand held spectrometers that costs thousands of dollars are extremely accurate. Here's a pic of the ones I'm talking about. Please, let's not confuse the issue by calling an ultrasonic tester an XRF spectrometer, as they're not even in the same class. ;) Handheld_XRF_Mineral_&_Metal_Analyzer.jpg
  11. TheFinn

    TheFinn Well-Known Member

    XFR testers are good, but as mentioned, only on the surface and depending on type, to a little depth. If something has a thick plating, they fail.
    Specific gravity is still very useful except when W is involved, and that goes for both.
    Oldhoopster likes this.
  12. fretboard

    fretboard Defender of Old Coinage!

    Very interesting since at least two of the coin shops in my area use the hand held XFR spectrometers regularly. They both have really expensive ones though, one shop paid over $14,000 and the other shop paid more than that. I'm thinking for purposes of operating a coin shop they're fairly safe to use as I don't think anyone would walk in with a gold bar or rock with much depth but it leaves me with some questions to ask at my local coin shops. thumbupp.gif
  13. TheFinn

    TheFinn Well-Known Member

    Just because everyone (who is anyone... obviously ) uses it, it doesn't mean it is infallable. It is good, but beatable. Fortunately, they must not be in an area with high-functioning criminals with means.
    Oldhoopster likes this.
  14. Clawcoins

    Clawcoins Well-Known Member

    This is interesting with the XRF device because in another thread

  15. Oldhoopster

    Oldhoopster It seemed like a good idea at the time.

    Doesn't matter if you use a $14000 handheld model or one in an analytical lab that costs more than 10x that, the X-rays only penetrate a short distance below the surface. Neither your coin shop nor the MIT Chem lab will be able to use XRF to differentiate between solid gold and thick gold plating. As Mr Scott used to say on the Starship Enterprise, "it's against the laws of physics"
  16. fretboard

    fretboard Defender of Old Coinage!

    No, there's plenty of criminals here in Sacramento but my guess would be if the coin shop owners get anything thicker than say a St. Gaudens double eagle then maybe they just say they're not interested in buying or testing. I don't know but I'll be sure to ask next time I'm in the area. I'd be interested to hear what they have to say about it and if they've ever been burnt. ;)
  17. justafarmer

    justafarmer Senior Member

    To tell the truth I am not sure what caused the readings to be what they were. I think it was probably a combination of factors. Depth of penetration, plus alloying of the underside of the copper plating with the zinc core caused by the pressures and heat generated by the coin strike. At this time I am not interested in investing in one of the devices. Was interested in seeing one in action though. Once the technology gets cheaper - I might reconsider. Heck - I still have some employees who can't grasp the iconcept of using a magnet for determining non-ferrous from ferrous scrap. Something as high tech and expensive to operate as XRF doesn't really fit our business model at this time.
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