Weight, dimensions, assay marks, and refiner reputation — here's how to check a gold bar is genuine before you buy, and what to do if something doesn't add up.
Short answer: check weight and dimensions against the refiner's published spec, confirm the assay card's serial number matches the bar, look for the refiner's melter/assayer mark, and buy from an established dealer — a counterfeit using a cheaper metal core almost always comes in underweight or off-dimension for its stated size, which is the single most reliable check a buyer can do without special equipment.
Every LBMA-accredited refiner publishes exact weight and dimension specs for each bar size they produce. A genuine 1 oz gold bar weighs 31.1035 grams — not "about an ounce." Measure the bar on a precise scale and compare the dimensions (length, width, thickness) against the refiner's own published spec sheet. Gold is dense; a counterfeit using a tungsten or other cheaper metal core to fake the weight will almost always be slightly off on dimensions, since tungsten and gold don't have identical density.
Most modern bars from major refiners (PAMP Suisse, Valcambi, Argor-Heraeus, and others) ship sealed in an assay card with a unique serial number stamped on both the card and the bar itself. Confirm the two numbers match, and that the card's tamper-evident seal is intact. Some refiners offer online verification tools where you can enter the serial number to confirm it matches a bar they actually produced.
LBMA Good Delivery bars carry a specific hallmark identifying the refiner — for example, Valcambi's bars carry a "CHI" melter's mark with "ESSAYEUR FONDEUR" (assayer-smelter) stamped in a rectangle. These marks are refiner-specific and documented; a bar missing the expected mark for its claimed refiner, or carrying a mark that doesn't match known references, is a red flag worth investigating before purchase.
Buying from a currently LBMA-accredited refiner (PAMP Suisse, Valcambi, Metalor, and the others covered on this site) gives you an active brand with ongoing quality standards and an easier path to verification. Buying a bar from a discontinued refiner like Johnson Matthey or Engelhard isn't inherently riskier — these were legitimate, respected refiners — but since no new legitimate supply exists, authenticity matters more and dealer reputation or third-party certification carries more weight.
A jeweler or dealer with an XRF (X-ray fluorescence) scanner can verify a bar's composition non-destructively in seconds. For anything you're not fully confident in — a private sale, an inherited bar with no documentation, an unfamiliar brand — this is worth the modest cost before you commit real money.
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