The human body mistakes radium for calcium
That biological error is why hundreds of dial painters in 1920s New Jersey glowed in the dark—and why most of them died young.
The United States Radium Corporation in Orange, New Jersey, encouraged its young dial painters to point their brushes with their lips. The technique kept the bristles fine enough to paint the tiny numbers on watch faces. The women were told the radium paint—marketed under the name Undark—was harmless. Some used it to paint their nails and teeth for parties. By the end of a shift, their clothing and skin glowed.
The body cannot distinguish radium from calcium. Once ingested, radium lodged in bone and irradiated the skeleton from within. By the early 1920s, women who had worked at the factory a few years before began experiencing what seemed like dental trouble. Then their jaws started to crumble. Teeth fell out. Bones fractured without cause. At least twenty-two dial painters died of radiation poisoning between 1922 and 1933.
The company insisted the women were suffering from syphilis and buried a Harvard physician's report that identified radium as the cause. In 1927, five surviving workers sued. They were so ill that observers doubted they would survive to see a verdict. Four days before the scheduled trial in 1928, the company settled for ten thousand dollars each. None of the five lived more than two years after.
The case directly influenced safety protocols on the Manhattan Project, where physicists recognised the similarity between plutonium and radium and designed their laboratories accordingly.