Topic: Bitcoin cannot be filled with Tungsten (Read 8631 times)

Using low frequency AC and a 4 terminal resistance would work well, but there is an even better way to do this.

Use transformer with an airgap. (Operating around 50/60 Hz. Negligible skin effect at 50Hz.) A sheet of conducting metal inserted in the gap acts as shorted "turn" in the secondary of the transformer. The energy lost is detectable in the primary and is proprtional to the thickness of the metal and inversly so to its resistivity. So I believe that you could calibrate such an instrument in millimetres of gold and, well if it was actually mainly tungsten, then the reading would show as having a thickness of about one-fifth that observed in fact.

Certain assumptions need to be made about resistive and magnetic losses in the the core, the size of the airgap, the flux that does not go through the coin etc, but such an instrument could be made. It has to be designed correctly in short. And if it had an airgap 1cm by 1cm by 1cm this would allow its use on coins (there is a whole factory making fake tungsten gold coins in china, and has been for ten years so we have not seen the end of this!!) as well as 10oz bars. This seems to me much better than we previously discussed since it allows a measurement to be made without spiky contacts on your expensive polished gold bar, and it allows you to make a measurement even if you have not got a genuine bar to test against. You need a set of calipers and this instrument: thats all. In fact you can probably do it by eye anyway!! If your gold bar is 5mm thick and the instrument shows its thickness as 1mm, its tungsten!!

The most difficult part of the prototype is finding a suitable transformer type core that I can either hacksaw an airgap in. It needs to be laminated for low eddy-current loss at 50Hz.

Make a couple assumptions here, but from Wikipedia an average size of a Good Delivery gold bar is 250mmx70mmx35mm. The resistivity of gold is 22.14nOhm*m.
(22.14nOhm*m)*(.25m)/((0.07m)*(0.035m)) = 2259nOhm = 2.26uOhm

If you had a bar of the same dimensions that was tungsten covered with a 5mm layer of gold, the bar would have an end to end resistance of 3.44uOhm.

Something like this micrometer should be able to measure the difference reasonably well.

IANAE but you don't "saturate" a bar. You apply a known voltage V and measure the current I, the resistance is R=V/I, you compare this against the resistance of a good gold bar (measured or calculated). You can do it with low current if you can measure things accurately enough.

I guess you are right...but good grief, how much current are we talking to saturate a bar?

That's only for AC of sufficiently high frequency, DC measurement should be fine.

uhhhh, skin effect?

Drop the coins on a table and listen to the ringing sound. Tungsten should sound different. Also, I am 90% certain you can't press tungsten the way that gold coins are minted. It's very brittle and hard. So the fine details on these coins are probably going to look different than on real minted coins.

I would also like to hear from anyone who has seen these coins in person. I have my doubts.

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.

@ guy who wanted to use ultrasound to test metal (or anyone w/o access to $100k+ equipment:
you might be interested in this:
http://www.youtube.com/watch?v=_T8fdshyEek

and this (by the people who uploaded the youtube video):
http://about.ag/UltrasonicThicknessGauge.htm

Sound wave velocity in tungsten is almost the double that of the gold, I don't know which kind of equipment is needed to measure them, but the difference is so relevant that I suppose it should be quite easy to spot.

Also, if suddendly a relevant percentage of gold held by bullions would be found false I suppose that would spike the gold price by quite a lot, since the real gold in circulation would be less that what was thought.

The screen shows Velocity L and Velocity S.  If I had to guess, I'd say Velocity L and Velocity S

Also, my understanding of waves in general suggests that one or more of those isn't a setting, but a measured parameter.

so i have access to an US that i'd like to use to scan my gold coins for integrity.  i was wondering if any of you guys know the velocity settings.  i captured this image off the Goldmoney video but see 2 different velocity settings that are quite far apart.  what do they mean and which one is the appropriate one?

Haha wow, the lengths people will go to make a dishonest buck. Sad.

This reminds me of the guy who bought a UPS on trademe and wondered why it wasnt working. When he opened it up, there was a brick inside instead of a battery

http://www.popgive.com/2008/07/dont-buy-ups-without-warranty.html

Someone actually attempted to sell me a fake silver morgan. Luckily I check all coins before I purchase. The coin was incredibly realistic. It was scary, especially since silver was only around $15.00 an oz. I wondered how is this remotely cost effective?? Then I did a bit of research and you could actually buy the fake coins for roughly $1.50 a coin, so yah it was actually incredibly profitable for the original scammer.

Best ad of the bunch: 

http://www.alibaba.com/product-gs/233194135/silver_coin.html

...and both of you are right to be worried:
http://www.alibaba.com/trade/search?fsb=y&IndexArea=product_en&CatId=&SearchText=silver+coins

this si why I only get my gold from gold vending machines

http://www.zurichgoldtrader.com/gold-vending-machine-opens-in-abu-dhabi-hotel/

Buy an ultrasound machine like the ones that dealers have, that's the only way to be sure. Otherwise, you can never be sure.

Now I'm wondering about fake silver.