In 1919 many black South African diamond miners were inspected by X-ray each and every day as they left. The mine owners were looking for diamonds that the miners would swallow or hide in self-inflicted wounds.
As I wrote back in 2013 for Pacific Standard magazine:
New technologies can do a tremendous amount of good. They can help us travel faster and farther, access information more quickly, and diagnose life-threatening diseases. But those same technological tools that accomplish wonderful things for the benefit of humanity can just as easily become the weapons of war, the spreaders of disease, and the tools of oppression. In 1919, X-ray technology found itself in the latter camp when it was used to inspect miners in the diamond-rich area of Kimberley, South Africa. Specifically, X-rays were used to see inside the black workers in the search for diamonds some were suspected of taking from white-controlled mines. Each day the miners would have to strip naked to be inspected. Some miners would swallow diamonds, or even hide them in self-inflicted incisions in their legs. But one diamond mine had the idea of using X-rays to find diamonds that couldn't be found through a simple strip search.
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Image: April 1919 issue of Electrical Experimenter magazine