Metallurgist Grigory Raykhtsaum shows Smithsonian three different ways to test whether something is solid gold: a color test,a thermal conductivity test, and a particle test. It’s all computerized now so all he has to enact is scan the object to get a read on the color, or zap it with an electrical current to degree the conductivity,and scrape a bit off to have it analyzed in a powerful microscope.
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Source: gawker.com