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Radium was discovered by Marie and Pierre Curie in 1898 [1] and was soon combined with paint to make luminescent paint, which was applied to clocks, airplane instruments, and the like, to be able to read them in the dark. [2] In 1914, Dr. Sabin Arnold von Sochocky and Dr. George S. Willis founded the Radium Luminous Material Corporation.
Radium paint was widely used for 40 years on the faces of watches, compasses, and aircraft instruments, so they could be read in the dark. Radium is a radiological hazard, emitting gamma rays that can penetrate a glass watch dial and into human tissue. During the 1920s and 1930s, the harmful effects of this paint became increasingly clear.
The first use of radioluminescence was in luminous paint containing radium, a natural radioisotope. Beginning in 1908, luminous paint containing a mixture of radium and copper-doped zinc sulfide was used to paint watch faces and instrument dials, giving a greenish glow.
In many cases luminous dials were implemented with non-radioactive fluorescent materials excited by light; such devices glow in the dark after exposure to light, but the glow fades. [14] Where long-lasting self-luminosity in darkness was required, safer radioactive promethium -147 (half-life 2.6 years) or tritium (half-life 12 years) paint was ...
The following year, a new facility at the Bloomsburg plant opened for the manufacturing of "tritiated metal foils and tritium activated self-luminous light tubes," [9] and the company switched focus to the manufacture of glow-in-the-dark exit and aircraft signs using tritium. Starting in 1979, the company underwent an extensive reorganization.
These particles excite the phosphor, causing it to emit a low, steady glow. Tritium is not the only material that can be used for self-powered lighting. Radium was used to make self-luminous paint from the early 20th century to about 1970. Promethium briefly replaced radium as a radiation source. Tritium is the only radiation source used in ...
Radium dial painters were instructed in proper safety precautions and provided with protective gear; in particular, they no longer shaped paint brushes by lip and avoided ingesting or breathing the paint. Radium paint was still used in dials as late as the 1970s. [27] The last factory manufacturing radium paint shut down in 1978. [28]
Undark was a trade name for luminous paint made with a mixture of radioactive radium and zinc sulfide, as produced by the U.S. Radium Corporation between 1917 and 1938. It was used primarily in radium dials for watches and clocks.