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Comment by tyingq | Hacker News Reader

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.

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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.

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