Actually, not that hard. The speed of sound in tungsten is easily twice that of gold, hitting it with a hammer and analyzing the response on the other hand will easily tell you that it's tungsten or gold. In theory, a smartphone app could do it.

You can also test shear forces on the bar, a test you can perform easily at the bank itself (or any of the other material forces tests really). Those do usually require a bit of machinery.

Lastly, you can measure electric resistance. A gold bar will have a different resistance than a tungsten bar, especially if you compare a frequency sweep AC resistance vs DC resistance (if there is a difference, which should be about 20nOhm/m vs 50nOhm/m for Gold/Tungsten, you know the material has a core that is different from the outside).

> Lastly, you can measure electric resistance. A gold bar will have a different resistance than a tungsten bar, especially if you compare a frequency sweep AC resistance vs DC resistance (if there is a difference, which should be about 20nOhm/m vs 50nOhm/m for Gold/Tungsten, you know the material has a core that is different from the outside).

Electric current mostly travels on the surface of a material. Gold-plated tungsten might not have sufficiently different resistance from pure gold, if the plating is thick enough.

This is only the case in AC (skin effect). DC penetrates the entire conductor.

The higher the frequency the less you penetrate the material (self-induction in the material forces the electrons outwards).

This enables you to effectively do a sweep of material composition by increasing frequency and measuring the resistance. In theory you could even tell if the core was not conductive at all (due to the resistance not changing despite lower frequency).

So even if the plating was thick, you would be able to tell because the resistance curve begins to change at lower frequencies due to Tungsten having a higher resistance.

If your device is really accurate you could even measure the rough area of the core since skin effect is proportional to the square of the resistivity.

That's why it makes senss to only buy gold cast in a thin shape (like a coin). It's much harder to cast in any meaningfully large tungsten core and it significantly raises the likelihood of that fake core being discovered as one can verify the authenticity of the gold piece by scraping away a millimeter or two of gold using basic hand tools.

Considering how expensive gold is per ounce, it's not like any of us will be buying it by the bar.

Maybe not those massive bars, but if we’re talking about being in a country where you can’t trust the government at all with the currency, wouldn’t you want to store most of your savings in gold or something similar? So just thousands of coins I guess? Arr me matey

> where you can’t trust the government at all with the currency

Executive Order 6102.

If you're in a country where you can't trust the government, you lost. The government can take away your gold, your government can take away your bitcoins.

If "the government has become the enemy" is a problem, then you've got bigger problems at hand.

Any SEM with an EDS system will tell you non-destructively if you have tungsten wrapped in gold. X-Ray diffractometry would also do the same. Rutherford Backscattering spectrometry too. All three of these techniques are non-destructive and the first two are quite common to find at universities.

I guess you and I have different intuitions about the meaning of the word "easy".

That's quite a leap from "you can verify at some other gold dealer" though.

It is also a very large leap from “let’s just drill it at random locations” that an actual gold dealer will try first if they suspect something like this. The drill bit not going through the bar like butter at the location will probably be the first tip-off.

meanwhile verifying bitcoin is trivial. hackernews is the one demographic i was hoping would understand that. has something changed?