The most reliable way to verify a gold bar starts before any test: a genuine bar arrives sealed in its assay card, with a serial number printed on the card that matches the serial number stamped into the bar itself. If those two numbers do not match, stop there. This guide walks through the full verification sequence — packaging and serial checks, weight and measurements against published specifications, simple at-home screening tests, and the professional instruments dealers use — so you know exactly how a gold bar is authenticated.
Specifications referenced are those published by the refiners and mints that issue the bars. Home tests are screening tools, not proof; professional instrument testing is the standard for a final determination.
Step 1: Check the Assay Card and Serial Number
Most modern minted gold bars are sealed at the refinery in a tamper-evident assay card (also called a CertiCARD or certicard). The card states the bar’s weight, fineness, and serial number, and carries the refiner’s mark and an assayer’s signature or stamp. Compare the serial number on the card to the number stamped on the bar — they must match exactly. Check that the seal is intact and the card shows no signs of being opened and resealed. If you have not read it yet, our guide to what an assay card is and what it certifies explains each element on the card. Some refiners also let you verify a serial number or scan a code on the packaging through their own verification services — use them when offered.
Step 2: Weigh It and Measure It
Counterfeiters struggle to match weight, diameter, and thickness at the same time, because gold is far denser than the metals used to fake it. Weigh the bar on a scale accurate to 0.01 g and measure it with calipers, then compare all three numbers against the refiner’s published specification for that exact bar. A bar in its sealed card weighs more than the bar alone — weigh unsealed bars directly, and for sealed bars compare the card’s stated weight using the maker’s published tolerances. A bar that is the right weight but visibly thicker than spec, or the right size but light, has failed verification regardless of how good it looks.
Step 3: Simple Screening Tests at Home
The magnet test. Gold and silver are not magnetic. A strong magnet (neodymium) should not attract the bar at all. Attraction is an instant fail — but passing proves little, because common counterfeit cores like tungsten are also non-magnetic. Treat this as a fast reject test only.
The visual test. Under good light, compare the bar against photos of a genuine example: lettering should be crisp and evenly struck, edges clean, surfaces free of the pitting, bubbling, or discoloration that betray plated fakes. Look for a seam around the edge — many fake bars are two halves joined around a core.
The dimension-and-weight combination. This is the strongest home check: tungsten’s density (19.25 g/cm³) is close to gold’s (19.3 g/cm³), which is why sophisticated fakes use it — but plated base-metal fakes, the common kind, fail the weight-versus-size test immediately because no cheap metal matches gold’s density.
Step 4: Professional Verification
When value matters, instrument testing settles the question. An XRF analyzer reads the metal composition at the bar’s surface in seconds. Ultrasound and eddy-current testers (such as the Sigma Metalytics verifier) probe below the surface, which catches a gold shell over a tungsten core that XRF alone can miss. A specific gravity test — weighing the bar in air and in water — measures true density with inexpensive equipment. Reputable dealers verify bars with these tools before buying them back, and many will test a bar for a walk-in customer. If a bar’s provenance is uncertain and the amount is significant, paying for professional testing is cheap insurance.
The Verification That Happens Before All of This
Every step above gets easier when the bar’s chain of custody is short and documented: bars bought from established dealers, kept sealed in their original assay packaging, and sold with their purchase records rarely raise questions at resale. The riskiest gold is the opposite — an unsealed bar from an unknown seller at a price well under spot. A discount deeper than the normal market is itself a verification failure: genuine gold does not need to be sold cheap. Keep bars sealed, keep receipts, and buy from sellers whose bars you will be able to sell back without an argument.
Shop Bars Sold Sealed in Assay
1 gram Silver Bar — Geiger (In Assay)
20 gram Silver Bar — Geiger (In Assay)
PAMP Peanuts Great Pumpkin 1/2 Gram Gold Bar (sealed card)
FAQ
Can a magnet prove a gold bar is real?
No. Gold is non-magnetic, but so are tungsten and lead, the metals most often used in fakes. A magnet can only reject a bar, never authenticate one. Weight, dimensions, and instrument tests do the real work.
Should I remove a bar from its assay card to test it?
Avoid it if you can. Bars kept sealed in their original assay cards are easier to resell and easier to verify by serial number. Weight and dimension checks can be done on most sealed bars using the refiner’s published specifications and tolerances, and professional testers can evaluate a bar without opening the card in many cases.
What is the most accurate way to verify a gold bar?
A combination: serial and assay-card match, weight and dimensions within specification, plus an instrument test that reads below the surface (ultrasound or eddy-current) or a specific-gravity density measurement. That combination defeats both plated fakes and tungsten-core fakes.
Does a serial number guarantee authenticity?
No — serial numbers can be copied. A matching serial is one layer of verification, not the whole of it. It matters most combined with an intact seal, correct weight and dimensions, and a trustworthy source.
Educational content only — not financial advice. This guide describes general verification methods; it is not an authentication of any specific bar. For a determination on a specific item, have it tested with professional equipment.