Radium, Tritium and other radioactive activators on watch dials and hands. Radium and Tritium contained as activators in luminous paint on watch dials and hands, besides other radioactive materials, are subject to never ending discussions amongst vintage watch collectors, especially those, who own lumed timepieces from earlier periods or are even working on them. Opinions differ from what concerns eventual health risks, not only amongst watch collectors, but also between professionals. Many ask themselves why those watches should still pose a threat to human health, whilst the ‘glow’ is long gone. True, the glow is gone - but not the radium (or many other radioactive substance used as an activator, as well as other substances following down the decay chain. The intention of this book is to give a general overview of radium- and tritium issues for the vintage watch collector interested in this subject. It is, in no way, addressing the physicists, chemists or nuclear scientists and will not go far beyond the necessary for a basic understanding, although a few more scientific issues could not be avoided. It is a book for all who are interested to look beyond a meager statement like: Luminous paint on watch dials and hands containing radium or tritium can be dangerous to some extend, especially when substances get inside the body, but all is relative and subject to different opinions. Content: Luminous paint in the watch industry - Luminescence, fluorescence and phosphorescence - Zinc sulfide - The activators, radium, tritium and others - Atoms, molecules and other particles - Radioactivity, radioactive decay, types of radiation, effects on health - Radioactive decay chain - uranium 238 to lead 206 - Strontium, the bone seeker / Promethium - Measuring radioactive radiation - Purchase of lumed vintage watches - Radon issues - Replacing luminous paint on watch dials and hands - What’s left? - Conclusion - The Radium Girls.