As I understand it, when radium is ingested (which happens when you use your mouth to point a brush containing radium paint), the body treats it like calcium, absorbing it into your bones. Without sufficient calcium, bones crumble. Since radium is radioactive, it quickly causes bone cancer. Many of the women who worked for Waterbury Clock and other companies using radium died horrific deaths from radium poisoning.
For more on the "Radium Girls" and their history, I recommend this article from 1996.
Although the dangers of radium were obvious, and very public, by 1928, using radium on watch dials continued until the 1960s. As of February 1, 1963, the sale of pocket watches with radium dials was banned in New York City, on the grounds that they exposed their owners to excessive levels of radiation. Wristwatches, however, were still considered safe.
By 1967, the general public was growing increasingly concerned about exposure to radiation. An article focusing on the dangers of X-rays mentioned that millions of bedside alarm clocks had radium dials, and compared the risk of wearing a radium-dial wristwatch to 30 years of nuclear fallout, a top concern of the '60s.
Manufacturers eventually abandoned radium in favor of less dangerous luminous compounds, but it wasn't out of concern for workers' safety: it was a response to public fear of being exposed to radiation by their watches.
A while ago, I had the opportunity to "play" with radium (don't worry, I did not touch it, breath it, lick it, or otherwise put myself in danger). I was given access to a box of Fitrite Radium Outfit, which has instructions on the label for coating the hands of a watch with radium. It would have been sold to watch repair shops, not used in factories.
|The label design suggests it might be from the 1930s.|
|Inside the box: small metal containers for the radium paint, a radium spreading stick, |
and a razor blade for scraping off excess radium from the watch hand.
|The radium paint in strong lighting.|
|The same container in complete darkness. I didn't have at tripod with me, so it's very blurry.|