'I was asked to paint dials," 15-year-old Katherine Schaub wrote in the spring of 1917, just as the United States was entering the First World War. "I said I would like to try it."

Dial-painting was the hot new profession for working-class women in the US: a lucrative, artistic and glamorous job that gave the mostly young employees a chance to work with the recently discovered wonder element, radium, as well as "do their bit" for the war effort.

They used luminous radium paint to make the numbers on watches, clocks and aeronautical dials glow brightly in the dark. And they were instructed to suck their paintbrushes, to make a fine point for the precise handiwork.

Speaking to a lawyer years later, dial-painter Mae Cubberley remembered: "The first thing we asked was, 'Does this stuff hurt you?' But [my boss] said no. He said that it wasn't dangerous."