Clocks with luminous dials – the danger within

I received an email from a blog fan this week who posed an interesting question. She was concerned that a number of clocks offered for sale at a local antique store had radium dials. I assured her that I know of no maker of mantel, shelf, or long case clocks that used radium on their dials but had there been alarm clocks, wristwatches, and even antique compasses on display her concerns would have been justified.

Westclox LaSalle alarm clock
Westclox LaSalle non-luminous alarm clock

As a matter of fact, it reminded me of the number of times I have been in antique and junk stores and have seen clocks with luminous dials and the danger I might have faced during a brief exposure, say within a meter or so and the more serious danger of being irradiated had I purchased and serviced them.

German musical alarm clock
German musical alarm clock or Joker

As a clock collector, I have a limited number of alarm clocks none of which have luminous dials. I understand the potential danger of radium and that is why I confine my collecting to alarm clocks with non-luminous dials only.

Even a clock that has lost its luminescence may still have traces of radium on its dial or particulate matter that has fallen from the clock face which makes them equally as dangerous.

Antique “alarm” clock mechanism from around 1900

Since radium has a half-life of hundreds of years even old radium dials are very hazardous. If working on a clock with a radium dial care should be taken to prevent the inhalation or ingestion of flakes or dust which may contain radioactive materials. My advice is to not work on them at all.

In the past several years radium dials have largely been replaced by phosphorescent – or occasionally tritium-based light sources. Therefore clocks produced after the 1970s had safer luminous material applied to the dials but modern alarm clocks are not nearly as attractive as antique clocks from the 1920s or so.

Clocks with luminous radium dials are certainly a danger to avoid and as far as I am concerned, not worth the risk.


2 thoughts on “Clocks with luminous dials – the danger within

  1. Ron, you ‘re right. Radium paint is dangerous.

    My career was in a nuclear power plant. Although my job duties seldom dealt with radioactivity. Can share some basic knowledge about it. There’s three forms of radioactive emissions. Alpha, Beta and Gamma. (Neutron a fourth, but too specialized to deal with here). Gamma is very penetrating. (What is used for x-rays). Lead shielding will stop it. Beta, stopped by a sheet 1/4 plywood. Alpha, is a low level emitter. Stopped by a sheet of paper.
    Where Alpha is dangerous is if the path of uptake oral. Once inside the body, radium in this case, mimics calcium and gravitates to bone. Although its a low field, once in position, will cause long term damage. (A great read is: “Radium Girls’ by Kate Moore. The tragic deaths of young women from cancers working in clock and watch factories early 20th century).

    What I’m trying to say, is YES, Alpha is dangerous. Although one would have to either ingest, inhale or absorb it. The fields from painted numerals on clocks or a vintage wristwatch are attenuated too low to be a health hazard.


    1. Thanks for your insights, Marty. Folks cannot leave stuff alone, the other day someone asked me to fix his father’s clock. It would have meant dealing with a radium dial, so in taking it apart, the dial would have to be separated and there is always the chance of ingesting residual particulates. Not a chance I want to take.


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