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 watch and clock dials.

What was Undark How did it work?

US Radium Corporation marketed their luminous paint under the brand name, “Undark.” It was a blended mix of glue, water and radium powder that was applied by the dial painters to watch faces, among many other products. ... Some of the early dial painters ingested very large quantities of radium.

Who invented Undark paint?

Dr. Sochocky, inventor of Undark™, founder of the United States Radium Corporation, and the man responsible for every drop of Radium paint on earth, would not escape the horrors of his creation. Toothless and fingerless, he died on November 14, 1928 at just 45.