Recently the national bank of Ethiopia discovered that much of the gold in its possession was fake
. It was simply gold-plated steel. It found this out after it sent a shipment of gold to South Africa, which promptly sent it back.
Theo Gray, writing for popsci.com
, points out that it's incredible that a national bank fell for a fraud like this, since simply by picking up the gold bars someone should have noticed that they were too light to be real -- gold being much heavier than steel.
Gray then considers a potentially very useful question: how could you create a fake gold bar that would be convincing enough to pass the pick-up test? The solution he comes up with is to use tungsten, which is about as heavy as gold, but much cheaper:
start with a tungsten slug about 1/8-inch smaller in each dimension than the gold bar you want, then cast a 1/16-inch layer of real pure gold all around it. This bar would feel right in the hand, it would have a dead ring when knocked as gold should, it would test right chemically, it would weigh *exactly* the right amount, and though I don't know this for sure, I think it would also pass an x-ray fluorescence scan, the 1/16" layer of pure gold being enough to stop the x-rays from reaching any tungsten. You'd pretty much have to drill it to find out it's fake.
Gray notes that it would cost about $50,000 to produce a fake gold bar in this way. But the bar, if accepted as real, would be worth around $400,000 -- which would be a pretty good return on your investment.