From Voice of America:
In the early part of the 20th century, the chemical element radium was widely believed to cure a number of ailments. It also was used as a way to create glow-in-the-dark faces on watches and clocks. The case of several women who painted those clock and watch faces in a small town in the Midwest state of Illinois helped to raise awareness to the dangers of radium, and forever changed labor laws in the United States.
What no one talked about were the harmful effects to humans caused by exposure to the radioactive radium.
Young women in their late teens and early twenties were recruited to work at the Radium Dial factory in Ottawa. They painted the faces of watches and clocks with radium, which caused them to glow in the dark.