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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. [1] The U.S. Radium Corporation was based in Orange, New Jersey. Undark was used primarily in radium dials for watches and clocks. Undark was also used for compasses, weapon sights, speedometers, telephone mouthpieces, fish bait, locks, and many more articles of use. [2] The people working in the industry who applied the radioactive paint became known as the Radium Girls [3] because many of them became ill and some died from exposure to the radiation emitted by the radium contained within the product. The product was the direct cause of radium jaw in the dial painters. Undark was also available as a kit for general consumer use and marketed as glow-in-the-dark paint. Radium was used to illuminate watches under safer practices until around 1968. [4]