Antistatic Brushes

Luminous paint for clocks was one of the first commercial uses for radium, and it was in watch-painting factories where the tragic consequences of internal radium exposure were first witnessed. Young women hired to hand-paint the numerals would point the paintbrushes between their lips, thereby ingesting the bone-seeking alpha emitter. Many developed devastating lethal cancers of the jawbone. Use of radium paint ceased in the U.S. by the late 1960s, but plenty of old clocks, watches, hands, and paint kits remain readily available today. A trip to a flea market or antique shop with a sensitive Geiger counter will often uncover scores of old clocks that used radium. People who collect and repair old timepieces should be aware that the paint is even more dangerous now than when fresh, since it has often lost its integrity and formed flakes which can be breathed into the lungs.

There was no standard formulation for radium paint. It contained the luminous phosphor zinc sulfide (ZnS) and a laquer binder, with a bit of a radium salt such as radium bromide or sulfate. Timepieces probably averaged about one microcurie apiece. Over the course of time, alpha radiation damages the crystal structure of the phosphor and it ceases to glow.

Modern luminous watches do not contain radium. They usually contain H-3 (tritium) or Pm-147 (promethium), both weak beta emitters that are much safer. Unlike radium, there are almost no detectable external radiations from these isotopes.