![]() ![]() ![]() The protective glass on the clock will stop most alpha particles, but will do little or nothing to stop beta and gamma particles. But move back 1-2ft and the levels drop down to background again, or rather close. Our measurements show that most vintage clocks are quite “hot” at close range (few inches or closer). Once you know the “dose” of radiation emitted by your clock you can be much better informed on where to store it, how often to handle it, etc. It is not unusual for collectors and hobbyists to own low cost geiger counters for this and similar concerns (rock collecting, vintage aircraft instrumentation, antique jewelry, glass and glazed stoneware, food studies, etc. The readings when the counter is placed near the clock should be compared to general background levels in our environment (typically 0.1 to 0.2 usV/hr). Depending on its date of manufacture, a clock could have also been illuminated with promethium or tritium (shorter half life and generally safer) or phosphorescent materials, more commonly available today which use no radioactive elements.īottom line is that the only way to know for sure is with a geiger counter. We also don’t know if and what kind of radioluminescent elements were used in the manufacture of a particular clock, especially post-1970. ![]() Clocks produced through 1970 could have dials painted with radioactive materials, so we must be concerned about deterioration that will ultimately occur. Most clocks produced in the early 1900’s (1900-1940’s) are found in this state, and this is a serious concern! Clocks produced after 1950 have not deteriorated to this point in our experience, but they may be well on their way to this level of deterioration. It is also important to consider that if the luminous paint is beginning to deteriorate and become powdery, that this powder or dust could be ingested, most notably through inhalation, and that could become a primary heath risk. These contaminants could possibly emit gamma rays, which are harmful and cannot be stopped without thick concrete and lead. References such as Wikipedia indicate that there could be contaminant levels on the order 3% present in the radium used. Since it is possible that other radioactive contaminants could be present as well, these need to be studied. We don’t really know the purity of the radium used in clocks over the years. Does this mean that at the right distance from the clock, radiation is acceptably low? To answer this question, we must also consider that beta particles are emitted at a lower intensity by radium-226, as well as other emissions (such as gamma rays). It is generally and commonly felt that since radium primarily emits alpha particles, and these are stopped by even something as thin as paper (so certainly the glass is an excellent barrier), that they are safe at about 1 ft away from the clock. Most luminescent paints purchased today basically “store” light and re-emit it at a different wavelength using an effect generally referred to as “phosphorescence.” This is in stark contrast to the “radioluminescence” of paints developed for clock dials in the early 1900’s which largely used radium-226 as the active element providing the energy to the salts in the paint (such as zinc sulfide or strontium aluminate) resulting in the “glow in the dark” effect. Radioactive paints are not commonly available today. It will be present despite the fact that the salts that produce the glow have been bombarded by radiation to the point where they have broken down and no longer glow. One extremely important note to keep in mind is that just because the “glow” has died away and your clock no longer glows in the dark (common with pre-1940’s clocks), this is no indication that the radium is no longer present! Quite the contrary, the radiation from radium-226 has a half-life of on the order of 1000 years. If you are a vintage clock collector, this movie is a must-see. The movie depicts very accurately the dangers of working with and ingesting radium-based paints, the suffering, pain and death that early 1900’s dial painters experienced in their young lives, and how they moved occupational safety forward. If you have not seen the movie “Radium Girls” (presently on Netfix), you should take the time to see it. Clocks produced in the early 1900’s are particularly concerning in this regard. Many folks might not realize that early vintage clock dials were painted with radioluminescent paint, which is a mixture of fluorescent salts (these produce the glow) and radium-226, which is a dangerous and highly radioactive element. ![]() We recently received an inquiry and decided to post the response here for general discussion. Folks sometimes write us to ask about the risks of owning a clock with a luminous dial. ![]()
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