The way coin dealers were doing it was to drill a small hole. But, people then want a discount on the bar. The best non-destructive way seems to be using an ultrasonic thickness gauge (but, they cost $100-$200 or so) because It is possible to use tungsten (which has a higher mass than gold) in gold bars, but it is quite difficult to do. It would likely be nearly impossible with 1 ounce gold bars/coins.Copper is diamagnetic (lead is, too), but neither exhibit the behavior nearly as much as silver. Copper is less diamagnetic than lead. Copper is less dense than silver, so weighing an coin/bar and comparing the dimensions to a real one would easily discover a copper-based fake (unlike lead, which can weigh the same as silver when alloyed with other metals).
Shows you how to use the "magnet test" to determine which 100oz Engelhard silver bar bar is real, and which is fake (made from lead).
Silver is diamagnetic, meaning that a magnet will not stick to it, but you will feel strong resistance when moving a strong magnet on the surface of the silver. Although lead is also diamagnetic, it is much less so, as this video shows.
Note that this test will likely not detect real silver bars that were hollowed and filled with lead (the ring test might, however).
The magnet test can positively determine that a bar is fake, but cannot positively determine that a bar is real. For a very accurate test, you can use an ultrasonic thickness gauge (check our our other videos to see one in action; we were the first to use this technique).
