Answer to Question #3561 Submitted to "Ask the Experts"

Category: Consumer Products — Watches, Clocks, and other Glow-in-the-Dark

The following question was answered by an expert in the appropriate field:

I am very keen on art deco and recently purchased a 1930s electric alarm clock on ebay^®. To my horror I noticed straightaway on receipt, though it didn't show in the photo, that it has luminous hands and figures. The glass face is intact and unbroken and the clock case is in good order. I have no intention of opening up the clock. Should I dispose of it? I really don't want to as it is a very good example of clock design from the period, but I would be grateful for your opinion as to the extent of the danger involved in keeping it.

The luminous clock face made in the 1930s almost certainly contains radium, a radionuclide with a long half life and a complicated decay scheme. That means, its emanations last a long time and consist of a mixture of alpha, beta, and gamma radiations of several energy ranges. However, the intensity of the radiation is quite low.

The only known radiation injuries from these radium-containing clocks, watches, aircraft instruments, etc., occurred during their manufacture. In the early days, the faces were painted by artists by hand with radium-containing paint. The artists habitually "tipped" their brushes in their mouths, to keep the point sharp. In so doing, they ingested small quantities of radium. Radium in the body is quite damaging. It is a calcium analog chemically, and concentrates in bone. Many of these early radium painters got bone cancer from their exposure. This experience, beginning in the World War I era, led to the first standards for limiting occupational exposure to radiation.

All of this says that you are at no measurable risk from your clock unless you somehow ingest or inhale the paint from the face. Many millions of clocks and watches were made with radium paint.

S. Julian Gibbs, DDS, PhD

Answer posted on March 26, 2004. The information and material posted on this Web site is intended as general reference information only. Specific facts and circumstances may alter the concepts and applications of materials and information described herein. The information provided is not a substitute for professional advice and should not be relied upon in the absence of such professional advice specific to whatever facts and circumstances are presented in any given situation. Answers are correct at the time they are posted on the Web site. Be advised that over time, some requirements could change, new data could be made available, or Internet links could change. For answers that have been posted for several months or longer, please check the current status of the posted information prior to using the responses for specific applications.