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Comment by daneel_w | Hacker News Reader

The product description goes into detail of how to produce a fake gold bar and how real their product appears, and even emphasizes that it passes common tests for authenticity - chemical, weight, resonance and even x-ray. "Our gold-plated tungsten bar and tungsten alloy golden bar are only for souvenir and decoration purpose". But, of course...

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Ultrasound testing is probably a weakness.

Edit: Sound passes through tungsten and gold at significantly different rates. Also, a "mixed media" type material would have extra "echos" that a homogenous thing would not.

Maybe a Differential Thermal Analysis/Thermomechanical Analysia? I suspect gold and tungsten have different behaviours when heated, and that should tell both apart.

https://en.wikipedia.org/wiki/Differential_thermal_analysis https://en.wikipedia.org/wiki/Thermomechanical_analysis

They have different magnetic susceptibilities. Gold is diamagnetic (repelled by magnetism); tungsten is paramagnetic (attracted). A strong magnetic field (neodymium magnets) and sensitive scales can tell them apart. I built a small rig a few years ago with parts from Aliexpress that worked for coins and for bars it's just scaling it up.

Looks like tungsten has more than twice the electric resistivity of gold. Setting up a conductivity test shouldn't be too hard.

Because of electrical current preferring the path of least resistance (the gold instead of the tungsten), and because of the Skin effect (https://en.wikipedia.org/wiki/Skin_effect), I suspect such a test would be inaccurate. Especially given how thick the plating is in these particular bars.

A high current test might work, albeit with some undesirable side effects :)

No skin effect for the direct current you could normally use to measure resistance. Accurately measuring the resistance of something as large as a metal bar can be tricky, but the gold would help as it does not oxidize on the surface.

The skin effect happens exclusively on alternating currents, and you will need a fairly high frequency for it to become a problem on the size gold bars usually have. So, no, it's completely irrelevant here.

Who doesn’t run chemical and x-ray fluorescence tests on their knickknacks?

To identify a gold-plated object, those would have to be done in a destructive manner, i.e. after scratching the object.

In many cases that would not be acceptable, so non-destructive tests may be used, e.g. based on density or X-ray absorption, but those are inconclusive, because tungsten also passes them.

When scratching the object is allowed, then there is little need for a complex test, as the change of color would be enough to show a fake.

Product description tells us that the gold plating is 1/16" thick (~1.6 mm), and that such thick plating of gold is necessary to fool x-ray testing. I don't know how invasive scratch tests are but I imagine the carving to be shallower than 1.6 mm. Their product is clearly and thoroughly designed for counterfeiting.

It is clearly designed for counterfeiting. If your concern and interests are truly limited to trade shows, I’m sure an ingot of steel painted gold would suffice.

If only they invested as much energy into spellchecking. I expect these come stamped "99.99 per cent gold".

Same as "massage toy" on AliExpress

"solvent trap"

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