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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, Radon 222, the next in line - Strontium, the bone seeker - Measuring radioactive radiation - Purchase of lumed vintage watches - Replacing luminous paint on watch dials and hands - What's left? - Conclusion - The Radium Girls.
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In memory of the Radium Girls
The Radium Girls, workers at the factory of the US Radium Corporation
With special thanks to Luigi Gori for making available images of lumed vintage watches from his collection.
Luminous paint in the watch industry
Luminescence, fluorescence and phosphorescence
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
Radon 222 – the next in line
Strontium – the bone seeker
Measuring radioactive radiation
Purchase of lumed vintage watches
Replacing luminous paint on watch dials and hands
The Radium Girls
1921 magazine ad for 'UNDARK', a product of the Radium Luminous Material Corporation (later U.S. Radium Corporation)
Radium (radium 226) and Tritium contained as activators in luminous paint on watch dials (numbers, markers, dots) and hands, besides other radioactive materials, are subject to never ending discussions amongst vintage watch collectors, especially those, who are looking for lumed timepieces from earlier periods.
Opinions differ what concerns eventual health risks, not only amongst the watch collectors, but also between the professionals. Many ask themselves why those watches should still pose a thread to human health, whilst the 'glow' is long gone. True, the glow is gone – but not the radium (or many other radioactive substances used as activators, as well as other elements following down the decay chain, with some difference explained later).
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. There will also not be any statements about any measured values affecting human health. This depends on too many factors and the topic is anyhow subject to controversial discussion.
Overall, it is a matter of high complexity and not as trivial as often presumed. Things are usually dealt with in a variety of shorter, specialized articles.
Any deeper interest must be referred to professional documentation, whereby this book will hopefully help to look in the right direction, already with a basic understanding.
In short: All of this is a more general treatise for the watch collector, also due to the fact, that the author is not in a position to contribute something of added value for the scientists in this field. This would furthermore involve detailed information, which is to 90% outside the core topic, with the inevitable result, that non-experts could soon no longer see the wood for the trees. Indeed, anything above the pure essentials would really require in-depth studies in that field to fully understand such a complex and multidisciplinary matter. Radioactive decay processes and the consequences are related to the work of physicists, chemists, biochemists or in the area of medicine.
The overall intention was therefore to produce a documentation that elevates itself somewhat above 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'.
On the other hand, it should – whenever possible – stay below a level where humble people would say: 'When most of a content is useless for a general understanding, things are called scientific'.
Nevertheless, some issues have, up to a certain degree, been dealt with in more detail. This is certainly not enough to make some watch collectors comfortable to stand behind the mike on a scientific panel dealing with radioactivity but should provide sufficient information to understand 'what's happening and why' and to make one's own assessment about any possible dangers to health.
When talking about threats from luminous paint on watch dials and hands containing radium, tritium (or other elements) as activators, one must distinguish between the pure collecting and/or wearing of such a watch, and collectors, who are also opening it up for whatever purpose, be it just to have a look at the movement or doing cleaning-, restauration- or repair jobs, especially if the dial is laid bare in the process. Things are also of vital importance in the process of professional servicing, -repair or -restauration.
The dangers arising from the application of luminous paint containing radioactive substances during the original production process are a matter of the past, as the new luminous products do not contain any radium, tritium or other radioactive elements anymore (or are, in the case of the use of tritium, kept in closed tubes).
It is not primarily the radioactive radiation and their influence from outside our body we have be afraid of today, but the fact, that the harmful substances – gases or scattered particles – can get into the body by inhaling (respiratory passages) or by digestion (through the esophagus into the digestive system) and from there also into the blood.
Radium and tritium are not the only harmful, originally applied elements, which can be found on vintage watch dials and hands. I have, however, largely restricted myself to these elements, as they represent by far the largest part. Others are, for instance promethium or strontium. The latter, because of its special danger, has been shortly dealt with in a separate chapter.
What concerns the different types of timepieces, the problem can mostly be found on lumed wristwatches from the early beginnings and up to the 1980s or occasionally even beyond. The more dangerous radium should only very rarely appear on watches after 1960.
Pocket watches are of course also affected, whilst they were already more and more becoming obsolete at the time of radium and later tritium as an activator for the luminous paint. If still produced as mass products in those periods – mostly until the time of the application of radium, we can often see a heavy application of this material. The size of the dial, well readable at night when lumed, often secured them a prominent place at the bedside table. This type of use, like with wristwatches frequently used in dim or dark environments, often triggered an over-rich re-painting after some time. And, of course, some clocks have similar problems.
Collectors storing lumed watches, especially from the 1920s to the 1960s, in unventilated areas in their house, could be absorbing dangerous doses of radiation. Recently, scientists tested a collection of radium-dial watches, which had produced radon- (next in line in the decay chain) concentrations very far above safe levels. Three of the watches alone were enough to go well over the threshold.
In any case, scientific research concerning the dangers originating especially from radium lumed watches, has substantially increased in recent times, with a clear tendency towards conclusions expressing a lot more concern than in the past (justified or not). We can also find an ever-growing number of special research work based on 'real' watches and collections, with in-depth measurements of radiation, types and amounts and not solely on theory.
Pocket watches are usually carried near the hips, often with the dial facing the body, with no shielding by the case, unlike with wristwatches, where the dial is facing away from the body (arm). The shielding by the case gives therefore much more protection. An exception are the wristwatches in plastic cases, but this is a generation of timepieces possibly dealing with tritium and not with radium anymore.
Above: Junghans wristwatch from the 1950s. Radium lumed numbers and hands. The luminous paint was undergoing strong decomposition in line with aging. The dial is burned to a brownish color. The crystal has been replaced due to damage by radioactive radiation. Very strong indication of radioactive radiation measured with a Geiger counter (see measured values later).
A watch is a nice thing to have, it tells you the time and possibly other things, provided there is enough light around. But what, if you are in low- or no light conditions?
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