How to Test Gold: Spotting Counterfeit Gold Bars and Coins
How to test gold most reliably: combine simple measurements with instrument tests. Most counterfeits already fail on weight and dimensions. Sophisticated fakes with a tungsten core, on the other hand, can only be detected with methods that look inside the metal.
What kinds of counterfeits are there?
Simple fakes consist of base metal with a thin layer of gold. They are usually too light or have the wrong dimensions. More sophisticated are bars or coins with a tungsten core. Tungsten has almost the same density as gold, so weight and dimensions often match.
There are also genuine gold coins passed off as rare years, and imitation packaging or certificates of well-known manufacturers. For bars, checking the serial number is part of the test.
First test: weight and dimensions
Every bullion coin and every branded bar has fixed manufacturer specifications. A 1-ounce Krugerrand weighs 33.93 g, is 32.77 mm wide and 2.84 mm thick. A 1-ounce Vienna Philharmonic has a diameter of 37 mm, a Maple Leaf 30 mm. With a precision scale accurate to 0.01 g and a calliper, you can check these values in a few minutes.
If the weight is off while the dimensions are correct, or the dimensions do not match while the weight is correct, that is a clear warning sign. A gold-plated silver disc of the same size would weigh only just over half as much, because silver has a density of 10.49 g/cm³ and gold 19.32 g/cm³.
Why magnet, acid and density are not enough
Gold is not magnetic. A magnet test therefore exposes fakes made of iron or steel. But tungsten is not magnetic either, so the test does not help against high-quality counterfeits.
Testing acid and X-ray fluorescence analysis reliably determine the gold content – but only at the surface. If a tungsten core is thickly coated with real gold, it passes both tests. Measuring density in a water bath cannot reliably detect tungsten either, because the difference from gold, 19.25 versus 19.32 g/cm³, is very small.
Testing methods that measure the inside
Ultrasound devices measure how fast sound waves travel through the metal. Sound travels considerably faster in tungsten than in gold, so a foreign core stands out. Other devices use electromagnetic methods and measure conductivity down to a certain depth.
Professional dealers use such devices when buying. For private individuals, buying one is usually not worthwhile. So have pieces from an unclear source tested by a specialist dealer before you buy them.
Buying safely instead of elaborate testing
The most effective protection is choosing the source. Buy from established dealers who source their goods directly from mints or refineries. Bars from manufacturers on the LBMA Good Delivery List have serial numbers and are often supplied in sealed packaging.
Be careful with offers well below the market price, private sales via classified ads and sellers who create time pressure. A price below the gold value makes no economic sense for genuine gold.
Visual features: strike, edge and colour
Genuine bullion coins have a sharp, detailed strike. Blurred contours, air bubbles, uneven lettering or misaligned obverse and reverse are warning signs. Ideally, compare the coin with the manufacturer’s images or with a piece whose authenticity is established.
Colour also gives clues. Pure gold at 999.9 parts per thousand has a rich yellow tone. The Krugerrand looks more reddish because of its copper content. A colour that does not match the stated fineness justifies a closer check. For bars, it is worth looking at the serial number and certificate. Some manufacturers let you verify the number online.
