Testing gold with a multimeter
October 20, 2011 9:02 AM   Subscribe

Testing gold using a multimeter


How do these work?
Do they measure resistance?
I have an inclination that perhaps I could use an ordinary multimeter to do this.

Are they as good as an xray? Can it determine Tungstun:
http://news.coinupdate.com/largest-private-refinery-discovers-gold-plated-tungsten-bar-0171/ ?
posted by jago25_98 to Work & Money (4 answers total) 1 user marked this as a favorite
These devices are using some kind of gel as part of the test, so it's not purely electric. I imagine the gel dissolves some of the metals used in the alloyed gold & the resistance is then a function of its purity.

I don't think they'll help you if you have a tungsten bar with a thick coating of gold round the outside.
posted by pharm at 9:39 AM on October 20, 2011

Looking at this page of similar items, it looks like these are small XRF (x-ray fluorescence spectrometers) devices, which is quite a bit different from a multimeter (though I'm not suggesting that you couldn't come up with a novel technique to use the multimeter). Given that they can determine a wide number of alloys, I'd bet that tungsten would be among the things it could analyze.
posted by pappy at 1:14 PM on October 20, 2011 [1 favorite]

If you think if it as a go/no-go test, the magnets are more useful than the ohmmeters.

Silver and copper are both better conductors than gold. Low resistivity won't tell you much of anything.

Gold is non-magnetic. Tungsten and some copper alloys are very weakly magnetic so one of the strong rare earth magnets available on that site could reveal a gold plated item.

But a gold plated bar of non-alloyed copper would fool any of these tests.
posted by three blind mice at 3:12 PM on October 20, 2011

They appear to (claim to) work by measuring the electrical resistance. The common gold alloys use silver, copper, nickel, etc. Alas, gold isn't the best conductor of the lot, so you could create a gold alloy that had an almost arbitrary resistivity. The color might be a give-away in many (most?) cases, though (adding silver makes gold appear white).

These devices can't tell anything about the material beyond the surface. They are far, far too inexpensive to be x-ray fluorescence machines. Think: kilo-buck class.

Also: tungsten is, for all practical purposes, not magnetic. It's technically paramagnetic but technically so is aluminum (and only about three times less susceptible than tungsten). It would take a whopping massive magnetic field to notice anything at all.
posted by introp at 10:26 PM on October 20, 2011

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