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The gold ingot test

Authenticating gold with magnets
Author: M. Müller, Germany
Online since: 11/02/2013, Number of visits: 86900

Authentication of gold

For centuries, the Archimedes principle has been used to test whether gold is genuine or not: If the weight doesn’t match the volume, the gold is tainted with a different metal. However, some time ago, counterfeit kilogram bullions with a tungsten core surfaced. Tungsten has almost the same density as gold and is therefore not detectable with the conventional method, while professional ultrasonic test devices are quite expensive.

Alternative test method

The assembly shown here uses a method of measurement based on the following principle: Gold is diamagnetic, tungsten paramagnetic. If the gold bar has a tungsten volume of approx. 30%, diamagnetism and paramagnetism cancel each other out. Therefore, if a magnet does not repel or even attracts the gold ingot, then, according to this test, the core contains other metals in addition to the gold.

Measuring procedure

The effect is measurable with micro scales that display two decimal places. The cardboard construction in the shown assembly serves as a spacer to protect the scales from the strong magnet. The ingot, which is not shown in this picture, must be placed into the narrow gap between the cardboard and plastic container. First, we measure without the magnet or, if possible, reset the scales to zero. Then the magnet is placed on the plastic surface without touching the test piece. The test shows that the gold ingot seems to have gotten heavier because of the diametric repulsion.

Weight difference

Para- and diamagnetism are very weak forces. Therefore, the weight difference caused by magnetic repulsion during this bullion test is hardly noticeable. For my 250 g ingot, I measured a difference of about  0,11 g to 0,13 g. The assembly shown here uses a block magnet Q-60-30-15-N and would also work for ingots weighing 100 g as well as heavier gold bars. Using the "DEATH MAGNET", it would also be possible to test single ounces (31 g), though there are currently no known cases of tungsten counterfeiting in small ingots or even coins.

Note from the supermagnete team:
Please refer to our safety tips when handling these relatively strong magnets, especially the chapters on Contusions und Magnetic field.