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The invention of radioluminescent paint can be attributed to William J Hammer who mixed radium with zinc sulfide (in 1902), and applied the paint to various items including watches and clock dials. In a case of bad judgment, he failed to patent the idea. Recognizing a good opportunity, a gemologist at Tiffany & Company, by the name of George Kunz, did patent it. Kunz and Charles Baskerville, a chemist, made their paint by mixing radium-barium carbonate with zinc sulfide and linseed oil.

At that time, at least in the US, radioluminescent paint saw little application. It stayed in the bottle. But in Europe, especially Switzerland, things were different. Quoting Ross Mullner "there were so many radium painters in that country that it was common to recognize them on the streets even on the darkest nights because of the glow around them: their hair sparkled almost like a halo."

The April 1920 Issue of Scientific American noted that more than 4,000,000 watches and clocks had been produced using radium-containing radioluminescent paint. The following items were identified in the article as containing radioluminescent paint: house numbers, keyhole locators, ship's compasses, telegraph dials, mine signs, steam gages, pistol sights, poison bottle indicators, bedroom slipper buttons, furniture locator buttons, theater seat numbers, automobile steering-wheel locks, luminous fish bait, and glowing eyes for toy dolls and animals.


During the 1920s, the radium paint was applied to clock and watch components in a variety of ways: painting it on with a brush, painting it with a pen or stylus, applying it with a mechanical press, and dusting. The latter procedure involved dusting a freshly painted dial with radioluminescent powder so that the powder would stick to the paint.


For wiping and tipping the brush the workers found that that either a cloth or their fingers were too harsh, but by wiping the brush clean between their lips the proper erasing point could be obtained. This led to the so-called practice of "tipping" or pointing the brush in the lips. In some plants the brush was also tipped before painting a numeral. The paint so wiped off the brush was swallowed."


It has been estimated that a dial painter would ingest a few hundred to a few thousand microcuries of radium per year. While most of the ingested radium would pass through the body, some fraction of it would be absorbed and accumulate in the skeleton. Later on, Robley Evans would establish a maximum permissible body burden for radium of 0.1 uCi.


As a result of the ingestion of the radium, many of the dial painters developed medical problems of varying degrees of severity. The first deaths occurred in the mid 1920s, and by 1926 the practice of tipping the brushes seems to have ended.