"The Radium Girls", 1920s

    In the 1920s, several US watch companies produced "glow in the dark" dials painted with radioluminescent paint, composed of zinc sulfide (ZnS) mixed with radioactive radium (²²⁶Ra) salts.  The employees hired to paint the dials were mostly young women. The paint was applied to the numerals with a small brush. As the brush became flattened, the women "pointed" the brushes on their tongues between applications, and thereby ingested a small quantity of radium each time.  Radium is an alpha-particle emitter that is chemically similar to calcium, and is therefore a 'bone seeker'. ²²⁶Ra accumulated in the long bones irradiated osteoblasts and other nearby cells in the bone marrow with high-energy, short-distance alphra radiation, and produced bone cancer and other genetic damage.  The graph shows that the incidence of bone cancer increases with an increasing "body burden" of ²²⁶Ra. [For more information, see "The Radium Girls"].

    Radioactive dials found wide use in military aircraft in World War II, and radium watches were manufactured into the 1950s [right]. Modern photoluminescent watches are light-activated, and do not use radioactive material.