So I'd like to ask the OP what it was that made him suspicious enough to risk cutting open a perfectly good bar? How did he know because I am not sure I would have been sure enough?

Next I would like to say that I am pretty sure that it would be quite a simple matter to measure the difference between filled and solid gold bars based on resistivity which would be a simple measurement to make in practice.

There are two key principles here - use a 4 terminal measuring device I would suggest that wooden or plastic block with contacts on the side and ends, could be used where the wooden block has an indentaion to match the exact size of gold bar. The principle of a 4 terminal resistance is that 2 terminals are used to inject a test current and 2 terminals used to read the voltage generated by this current. This cuts out completely voltage generated by poor contacts or leads.

Its not necessary to use a particularly large current - modern amplifiers are capable of accurately measuring very small offset voltages, and you are measuring a true differential voltage here that makes it a lot easier.

The last 'trick' which would add a little to the cost of what I have so far described a very simple cheap instrument, would be if it did in fact turn out to be too difficult to measure the offset voltage accurately due to offset noise in the amplifier. In this case you instead use an alternating current to perform the measurement and a synchronous decode to accurately measure the offset voltage. Such a decoder will reject all other frequencies including DC so that you only have the signal you want. I dont think this would be required, but it could be.

I can see that provided that you were happy to have an instrument that effectively only measured one size of gold bar, it would be very easy to devlop such an instrument. How could it be made more general purpose (to cater for many different sizes?). Not sure. To compare the same sized gold bar, its essential to have the contacts in the same place.

Indeed perhaps the hardest part (really) is that if I did this you'd have to loan me a few genuine bars to calibrate it! (As well as the fake!)

If there IS anyone who wants such an instrument I do actually have relevant experience to develop such a thing and am looking for work right now. Please PM me. It wont be cheap for a 1-off instrument, but it WILL work (I'd do a better feasibility study first. and it could save you a small fortune!! ) It would also be pretty interesting in that I have never heard of such an instrument but am pretty sure I could make one.

Chief Bone Necklace trades 1000BTC for his daughters sacrifice lmao
/let me stop

Now if look you closely at this post, just can see it's pretty obvious that the poster has absolutely no idea what they are talking about. Of course this isn't proof of total ignorance. A simple explanation is that it was a quick trolling without particular attention to detail. I'm not one of these people who are convinced of blanket trolling, although given the recent trolling posts and the whole trolling game taking place I consider it a strong possibility.

Are we going to see watercooled ASICs?

There should be negative choices as some of us make a living with bitcoin.

Shut up and take my money !

Here is a way to test without ultrasound equipment.

First dip gold in water to find the amount of displacement.  The displacement will give you a very accurate volume of the bar.  Now using a scale measure the weight of the bar.  Using the volume and the atomic weight of gold you can also calculate weight.  If the calculated weight and measured weight are the same it's a real bar.  If it is lighter then it might have tungsten in it.  Something like that.