How do you check a gold bar is real, the way a dealer does?

Big Bullion · Published 27 September 2026 · Updated 27 September 2026 · 4 min read

Reviewed by the Big Bullion team, 27 September 2026

We weigh and measure every bar against the refiner's own published numbers, run a magnet test, and check it with ultrasound and X-ray fluorescence before it changes hands. A sealed bar's assay card and the refiner's place on the LBMA Good Delivery list add confidence, but neither replaces testing the metal itself.

What we check on every bar

Every bar and coin that crosses our counter goes through the same checks, in front of the person selling or buying it. None of them mark the metal, so a genuine bar leaves in exactly the shape it arrived.

Weight and size against the maker's own numbers

A refiner publishes an exact weight and a set of dimensions for every bar it makes, because a Good Delivery bar has to match a stated specification, not only a stated purity. A genuine 1 oz gold bar sits just above 31.1 g, because refiners over-pour slightly to guarantee the stamped minimum. Put a bar on a calibrated scale and measure it against those published numbers, and most counterfeits fail before anything else is tested.

The magnet test: a five-second first pass

Gold and silver are not magnetic, so a strong magnet is a fast first check. A bar that clings to a magnet, even weakly, is not what it claims to be. It only catches the simplest fakes, though, because a more convincing one uses a core of tungsten or another dense metal that is not magnetic either, so a bar that passes the magnet test still goes through everything else.

What ultrasound and X-ray add

Tungsten weighs almost exactly what gold weighs, which is why the better fakes use a tungsten core to beat both the scale and the magnet. Sound travels through tungsten about 38% faster than it travels through gold, so an ultrasonic probe reads back the wrong thickness whenever tungsten is hiding under a genuine-looking shell.

An X-ray fluorescence scanner reads what the surface itself is made of, to about 0.01% accuracy, in under 20 seconds. It only sees the outer 20 microns or so of the metal, which is why we never rely on it alone, but it is very good at catching a bar that is plated rather than solid.

The assay card and the serial number

A minted bar usually comes sealed in a card carrying an assay certificate and its own serial number. That card is a convenience, not a test in its own right, because paper and printing are easier to copy than the metal underneath. We test the bar whether the card is there or not, and a serial number that does not match, or a card from a maker we cannot place, is one more thing worth asking about.

Checking the refiner: the LBMA Good Delivery list

The LBMA Good Delivery List names every refiner currently accredited to the standard the wholesale gold market trades on, and anyone can look a name up on it. Read 27 September 2026.

PAMP, Argor-Heraeus and Metalor, the refiners behind most of the bars sold here, all appear on that list. Being on it says the refiner meets the standard for purity, weight and physical appearance the market trades on. It says nothing about the one bar in your hand, which is what the tests above are for.

What happens if a bar does not check out

If a bar fails any of these checks, we do not buy it and we do not sell it, and we tell the person in front of us exactly which check it failed. What happens to that piece afterwards is a matter for the person who brought it in, and not something we can speak to.

We sell physical gold and silver. Nothing on this page is financial advice.