Radium Glow

A few weeks ago, I decided to bring a vintage Ingersoll mechanical alarm clock out of storage and place it on display in my bedroom. It has a large, dark blue Bakelite case and a chrome plated bell that completely covers the back. The dial, with its old-fashioned numbers font and simple swords handset, are especially pleasing.

Although I’ve owned the clock for nearly 30 years, I had never analyzed the crackly, deteriorated luminescent coating (lume) on the numbers and hands. After shining a standard flashlight or even a UV light on the lume, the glow would quickly fade away within about two seconds. I assumed that the lume was old and worn out like normal luminescent paint becomes after several years.

However, now that the clock is displayed on the nightstand where I can stare at it for long periods of time before falling asleep, I became more curious about the clock’s lume. The curiosity peaked when I began noticing that the lume was emitting a faint glow long into the night. The desire to determine whether or not the numbers and hands were coated with radium-based paint came to light.

The next day, I placed the clock inside of a light resistant wooden box, and placed the box into a dark closet. The boxed clock remained in the closet for two days. On the third night, I brought the box out of hiding then opened it in my almost totally dark bedroom. This would help to avoid any chance that stray light might “charge” up the lume.

I removed the clock from the box and discovered that the numbers and hands emitted a very faint, green glow. This meant that the test for radium came up positive. I then took a few long exposure photographs of the clock for future reference.

After researching the history of Ingersoll company’s clock and watch radium lume use, all of the clock’s aspects matched the necessary criteria. I found out that the numbers’ and hands’ lume paint looked crackly, due to the fact that radioactivity degraded the paint’s integrity relatively quickly. The markings no longer glowed brightly not because the radium petered out; but because the luminescent chemicals in the paint were mostly destroyed by gamma radiation. The nearly full force of gamma radiation was still present.

I consulted the U.S. Nuclear Regulatory Agency to find out if I there was any danger in keeping a radium timepiece. According to the NRC, there are no problems as long as the crystal glass is fully intact with no cracks. There will be a small amount of alpha radiation which is lower than our normal background radiation. On the other hand, if the dial is not covered by a case and a glass crystal, it is possible for gamma radiation and higher doses of alpha to escape. It is not adviseable to wear a radium watch with a damaged crystal.

The agency also cautioned against amateur repairs of radium lume because the extremely fine powder could be inhaled or accidentally ingested. Gamma and alpha radiation are not stuff we want inside of our bodies.

If the timepiece owner decides not to keep the radium dial, he/she should notify his/her home state’s or province’s environmental protection agency for advice. The NRC reminds us that radium has a half-life of about 1600 years, so the substance will be viable for a considerable length of time.

If you have a timepiece that contains radium, your locale might or might not have license requirements. Some municipalities require general license permission from the NRC depending upon the amount of radium in their clock or watch. Regulations vary from place to place, so if you own a radium timepiece and are uncertain about the legal technicalities, it is best to check the Nuclear Regulatory Commission’s website for information regardless of whether you plan to keep or discard the radium.

In the vast majority of cases, there is nothing to worry about. Also, it is important to differentiate between radium lume and tritium lume. Ra-226 emits both gamma rays and alpha radiation; while tritium (an isotope of hydrogen) only emits beta particles. If you own a tritium lumed watch, the beta radiation cannot penetrate the glass crystal of the watch. Also, the half-life of tritium is 12.3 years. Keep in mind, that conventional, light activated luminescence on the vast majority of contemporary wristwatches does not contain any radioactive material whatsoever.

Consumer grade radioactive material is a fascinating, multi-faceted subject of study. I’m glad I decided to bring out the old Ingersoll clock to enjoy.


The Blue Jay of Happiness quotes Polish-French chemist and physicist, Marie Curie. “The various reasons which we have enumerated lead us to believe that the new radio-active substance contains a new element which we propose to give the name of radium.”

About swabby429

An eclectic guy who likes to observe the world around him and comment about those observations.
This entry was posted in Health, Hobbies, Hometown, Science and tagged , , , . Bookmark the permalink.

11 Responses to Radium Glow

  1. wjwingrove97 says:

    I like this

  2. Alien Resort says:

    Kraftwerk hadn’t fully entered my mind until I got to Marie Curie.

  3. GP says:

    I haven’t seen or heard of those alarm clocks in ages! Thanks for teaching me more about radiation.

  4. Clocks like this one are in fact ticking bombs. Thanks for the in-depth research. I doubt if many owners understand what they are dealing with or how to safely dispose of them.

  5. Jeff Flesch says:

    That’s fascinating. I had no idea this was a possibility.

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