Gold-filled vs solid gold: how to tell the difference

Discussion in 'European & Other Pocket Watches' started by jboger, May 12, 2020.

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  1. jboger

    jboger Registered User

    Jan 7, 2019
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    My question is quite specific. In the absence of any wear, and in the absence of any quality marks, is it possible to distinguish a gold-filled case from a solid gold case by some non-destructive analytical means?

    John B
     
  2. Ethan Lipsig

    Ethan Lipsig Registered User
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    I have a great deal of experience with solid 14k and higher solid gold pocket watch cases. Unlike gold-filled cases, the back covers on solid gold pocket watches all flex a bit when I press their centers with my finger. I once had a lovely 14k V&C that flexed alarmingly, which is why i sold it. Even heavy solid gold cases flex when pressed. Little ladies sold gold watches also flex when pressed but, because of their small size, the flexing is hard to detect. In contrast, I have never come across a gold-filled case that flexes when pressed. The base metal in their cores is much more rigid than gold.

    I believe there are more scientific methods for determining whether a case is solid gold, e.g., some sort of expensive electronic tester, but I will leave it to others to describe them.
     
  3. glenhead

    glenhead Registered User
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    There is no definitive non-destructive test possible without laboratory-style equipment, no. Gold-filled means a mechanically-bonded layer of thicker-than-gold-plated gold (roughly five to ten times thicker) on a substrate. In many situations a water-displacement test can be used (I'll let you look that up yourself), but there are substrates where the difference is too close for a definitive call. In a lab you can use x-ray and sonogram tests.

    Glen
     
  4. Dr. Jon

    Dr. Jon Moderator
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    I suggest a non destructive test. Archimedes invented it in pre Roman times.

    Remove the watch movement from the case along with the crystal and any other non case parts. Weigh the case. Now put the case in a beaker of water and measure its displacement. Gold in various alloys has a density if between 14 and 19. Brass and steel are about 7.5.

    This method is not highly accurate because air bubbles and measuring beakers are not that precise or accurate but it is probably good enough to tell the difference between gold filled and solid gold.

    If you can rig a precision scale to hang the watch directly from an arm you can do better. With this set up, weigh the case in air and then weigh the case in water. The difference in weight in grams is the volume in cubic centimeters.

    I know of a few ways to defeat this scheme none of which is much concern. Method one actually used by some very ignorant counterfeiters is to replace the precious metal with platinum (They actually replaced silver with platinum to counterfeit US silver dollars and some one in Russia made platinum Samovars to counterfeit silver ones) . I'd love to get cheated that way!

    Tungsten and Tantalum are also dense enough to match density of a gold case. I doubt any one did such a switch because both metals are very difficult to work but gold over disks over tungsten or tantalum could be dense enough to fool this method.

    Lead won't work. Its density is about 11.
     
  5. Greg Frauenhoff

    Greg Frauenhoff Registered User
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    Ethan's approach is the one I generally use, but it is worth noting that in the old days some shysters made non-gold watch cases that were intentionally flexible. I don't know what alloy was used. Or maybe they just made the lids thinner(?). Some of these fake gold cases are very very good.
     
  6. Greg Frauenhoff

    Greg Frauenhoff Registered User
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    Dr. Jon's approach is a good one but not without difficulties (as he noted). I've used it with success in identifying solid gold bows (many of which are 10k). For cases, in addition to bubbles, another practical problem are the non-gold bits such as springs.
     
  7. jboger

    jboger Registered User

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    Thanks to everyone who responded. I am familiar with the technique. One first measures the volume of an irregular shaped object (like a watch case) by measuring the volume of displaced water in a graduated cylinder. Knowing the volume and the mass, one then gets the density of the material and compares that value with the density of other materials. And hopefully the range of other values is outside the uncertainties in the measured density of the case. Got it. I was hoping there were some simple spectroscopic technique or other method. But perhaps not. Thanks again.
     
  8. Dr. Jon

    Dr. Jon Moderator
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    Spectroscopic acid touchstone and conductivity and even cupulation only test at or near the surface. I suspect that assay offices measure density to supplement their surface tests.
     
  9. John Matthews

    John Matthews Registered User
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    The Birmingham Assay Office ...

    From 1998 major investment was made in exploring X Ray Fluorescence as an alternative assaying method. This became established as an accepted process and further investment in the hi-tech equipment necessary moved all assaying to XRF by 2005. The traditional cupellation and titration methods for gold and silver respectively still remain the referee method in case of uncertainty.
    X-rays of energy 50keV have a 1/e penetration depth into Au of 71 microns

    John

     
  10. MartyR

    MartyR Registered User
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    There is a common device called an "XRF Analyser" - I think that XRF stands for X-ray fluoresecence - which is a hand-held device costing around $5,000 or a lot more! The device is spectographic and non-destructive, and in addition to identifying metalcontent can be used to identify gemstones. Many larger pawnbrokers and jewelry stores have one of these, and if you have a particular piece you need to identify, just ask for a (free) valuation :)
     
  11. Bryan Eyring

    Bryan Eyring Registered User

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    Answer:

    Yes - knowledge.
     
  12. Jeff Hess

    Jeff Hess Moderator
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    Ethan is correct. I am confident that I an (yes bragging) tell 99.9 percent of the time if a case is "karat gold" or gold filled upon a 5 to ten second inspection.

    (I might add to Ethans's excellent post, that I have seem some early giant cases (most notably a 5 ounce rocket for gold case) that did not and would not "flex".)

    It really is pretty easy.

    I have even "for fun" gambled on the "look" of cases on internet sites that were noted as "gold filled" that I gambled would be gold. (and out of the dozens I have gambled on with just an internet pic) only one was not gold)
     

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