Undark

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 1926. The U.S. Radium Corporation was based in Orange, New Jersey, but was not the only radium-painting business in the United States. Other big names in the early 1900s include the Radium Dial Company and the Luminous Processes Inc.