A century ago, glow-in-the-dark watches were an irresistible novelty. The dials, covered in a special luminous paint, shone all the time and didn’t require charging in sunlight. It looked like magic.

In 1917, an Italian-American woman named Amelia Maggia started working at the U.S. Radium Luminous Materials Corp. in Orange, New Jersey, when she was just 19 years old. Her job was to paint soldiers' ...