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Luminous Watch Dial RisksTable of ContentsTypes of Luminous Dials
Types of Luminous DialsMany vintage watches, especially military watches, have gold or whitish colored "paint" on the hands or on the numbers on the dial. This paint is quite likely made of a phosphorescent compound mixed with radium. This causes, or at least used to cause, the numbers and hands to glow in the dark. Unlike many glow-in-the-dark compounds, these would glow all night long and would continue to glow for years on end. After a while (25-50 years?) the paint will be destroyed by the radiation from the radium so chances are these watches will no longer glow in the dark.The radiation from these radium dials have the potential to cause various health risks and should be handled in ways to minimize these risks. I am not an expert in this field, but I have tried to collect as much information as I can so that you can evaluate how you want to deal with these dials. Corrections and suggestions are very welcome. Besides radium, there are several other methods of making "glow in the dark" watch dials. There are various non-radioactive phosphor compounds that will glow in the dark after being exposed to light. Some modern compounds can glow for 10 to 15 hours after a relatively short exposures to bright light. Tritium, like radium, is radioactive, but it is much safer. Tritium, a form of hydrogen, has a reasonably short 12 year half life so it doesn't have the long term dangers that radium has, and it decays into harmless helium. The beta particles that tritium gives off can not even penetrate the outer layer of dead skin on your body, let alone the watch crystal and watch case.
Identifying Luminous DialsThere are three primary ways of identifying what kind of luminous paint is on a dial.First, beginning in the 1950s or 1960s, watches that used tritium would either have two small "T"s on the bottom of the dials by the 6 or have "T<25" labels. The "<25" means that there was originally less than 25 milliCuries of radioactive tritium. Watches that used radium would similarly be marked with an "R" or "Ra". This technique will not work to identify earlier watches. Secondly, you can use a dosimeter or a Geiger counter to measure the radiation levels. Radium will show up, but tritium and non-radioactive glow in the dark compounds won't. Apparently, the emissions from tritium are so low in energy that you need special detectors to even measure it. Finally, and maybe the most common way, is to judge the age of the watch or clock. Based on the age, a reasonable guess can then be made. Luminous radium dials were first used around 1910 before the dangers of radioactivity was fully understood. Radium dissolved in water was even sold as a health tonic and said to increase your energy levels and cure diseases. After WWI and through out the 1920s, radium dials became popular and were widely used on watches and clocks. In the late 1920s, it became obvious that the girls and women who painted the dials were suffering and sometimes dying from health complications caused by the radium. The widely published liability trial of the "Radium Girls" caused the popularity to wane in the 1930s, but radium dials were again used widely during WWII. The vast majority of watches or clocks made before 1950 that have a thick yellowish or white paint on the hands or dial are made with radium. During the 1950s and 1960s, the dangers of using radium was recognized and it was phased out in the US. Instead, either non-radioactive phosphorus compounds were used or various tritium compounds were used. Other countries, especially third world countries, still use radium. For example, Iraqi tanks captured during the Gulf War had radium dials on gauges. In the last decade or so, tritium has also started to be phased out. Despite its lower risk compared to radium, it is still radioactive resulting in more red tape. The non-radioactive modern glow in the dark paints are often considered to be a better solution.
What Are the Risks of Radium Dials?I have never gotten an explanation of exactly how risky these radium watch dials are from someone who I would judge to really know what they are talking about. Many people have a little knowledge and make claims that range from "immediately call your hazardous waste disposal people", to "hey, watchmakers have been cleaning these watches for decades, and there isn't any signs that this is any more dangerous than crossing a street."The primary health risk of Radium is that it is radioactive and if it is ingested or if dust particles containing radium are inhaled, it can lead to various bone diseases and forms of cancer. While there is no safe level or radiation exposure, everyone is exposed to a certain amount of radiation every day. The question is: "are the levels of radiation from the radium dials high enough to worry about?" Not all the radioactive material remains where the paint is visible. Over time, this paint will become very dusty and it is important not to breath any of this dust. The watch crystal should not be removed without a good reason, nor should the watch case be opened up. The dust is due not only to the normal aging of the paint, but also because when radium breaks down, the force of emitting the alpha particle during the radioactive decay causes the daughter atom to recoil. This recoil is strong enough to break the chemical bonds that holds the atoms in place. The resulting daughter atoms will move a little ways away and then settle. These daughter elements, such as radon-222, polonium-218, lead-214, and such, are all radioactive and just as much a problem as the radium.
If you do a web search on the Radium Girls, you will find lots of stories on them. Many of these stories are nearly identical, but one of the better articles is by Bill Kovarik. Now, this might sound very frightening, but these women ingested a LOT of this paint, "only" a few died, and probably not more than 20%-40% had health problems. It is not clear how many of these health problems were due to the radiation or due to the heavy metal poisoning. There are lots of risky activities in this world, from crossing the road to eating fatty meat, that most people don't think twice about doing. However, people seem to panic as soon as you mention radiation or "mad cows disease". On the other hand, ingesting this radium may be significantly less of a problem than breathing it. Ingested radium will either pass through your system, or act chemically like calcium and enter your very slow growing bones. The CDC's Radium webpage says that 80% of ingested radium will pass directly through you and some of the rest will eventually be filtered out by your kidneys. Radium dust in your lungs, on the other hand can stay there and potentially cause lung cancer. One particular concern of radium decay is the daughter element radon-222. Radon is a noble element so it won't chemically rebind and it is also a gas so it will float away from the dial. Radon has a half life of about 4 days, which is probably enough for it to diffuse to anywhere in the watch case but probably not long enough to escape before it decays. The daughter elements of radon-222 are radioactive solids, which will settle on the watch parts. So, it seems likely that a watch with a radium dial will cause the entire movement and inside of the case to be covered with a very find dust made of radioactive material. Again, I am not an expert here, so this may or may not be a real problem, I don't know. I've, however, read discussions about how entire boxes and cabnets have become radioactive due to storing small amounts of radium in on spot. Now it is true that as time goes on, the break down of the radium will cause it to lose some of its potency. Unfortunately, the half-life of radium-226 is about 1600 years, so these watches will be about as radioactive 200 years from now as they are today. For all practical purposes, these watches will be radioactive forever. One final comment on the possible health risks of radium is that the dial painting companies weren't exacting in their formulas. It wasn't just radium-226 that was used, but a variety of different radioactive elements. Most of these other elements will decay faster than radium-226, so they may be less dangerous now. Also, depending on how the paint was mixed up, some dials were very hot, while others were not. If you are concerned about a particular watch, you should have it measured. Anything else is just a guess.
Reference InformationWhile the risks described above are as accurate as I know how to make them, it is probably best if you evaluate the data yourself. The following are some of the sources I have found on this subject.A little more information on radium can be obtained from the CDC's Radium webpage. However this page deals more with Radium in the ground or drinking water rather than watches.
Yet another reference, Obtaining Radium published in 1974 in 'The Journal of Chemical Education", talks about how to remove the radium from watch dials for use in class room demonstrations. It states: "Treat the radioactive materials during procedures with thoughtful respect and your maximum exposure dose per clock face or compass dial will not exceed 1 milli rem. The hazards of radiation of this amount are far less dangerous than the dozens of toxic, caustic, and corrosive chemicals that students handle in a school year.Somehow, I suspect that one of these two references is wrong.
In the June 1988 issue (vol 30/3 num 254 page 225), there is a short article by Robert Free of the Texas Department of Health, Bureau of Radiation Control. Two relevant quotes are: Individuals manufacturing the jewelry [made from old watch parts] are exposed to dusts containing radium from buffing and brushing exposed watch faces, dials and hands. As a result, they run an increased risk of cancer from ingestion and inhalation of radioactive particles. People who repair and refurbish old watches are also at risk. In addition, contamination of the workplace is a serious problem. Decontamination can cost thousands of dollars.Also Texas is one of many states which has adopted rules prohibiting the use, possession, manufacture and distribution of radioactive material without a license. That includes the distribution of radium contained in costume jewelry and watch parts. In an article from December 1974 (vol 16/6 num 173 pg 754), Henry Fried basically says that the luminous dials that use tritium are very safe and that unless you are have clock from the 1920s or 1930s, you almost certainly don't have a radium dial. Henry Fried is a noted author of watch books, but I don't know if he is also an expert on radiation. The article sounds very reassuring, but he never actually says that radium dials are safe, dismissing them as being almost non-existent because there is no "R" by the dial of most watches that he has seen. Unfortunately, I don't think the "R" marking for radium was used until the 1950s or 1960s. Then there is a series of three short articles on the subject. In the first article, from December 1984 (vol 26/6 num 233 pg 732), it is reported that a luminous radium dial on a wrist watch was measured with a dosimeter at 12 mrem/hr. It was noted that individuals working with radiation are permitted a weekly does not to exceed 100 mrem/wk and caution was advised when handling and wearing these watches. In a reply to the above article, published in the Jun 1985 (vol 27/3 num 236 pg 336), it is claimed that just measuring a watch at the crystal is misleading. The 100 mrem/wk amount detected by the badges worn by nuclear workers assumes that the entire body receives that dose and a point source like a radium dial is much less dangerous because it effects a much smaller area. It is calculated that you would need to cover your entire body with 3000 wrist watches emitting the 12 mrem/hr to make it equivalent to a nuclear worker receiving the 12 mrem/hr. Although it wasn't calculated in the article, if you take the difference in area into account, this would make the watch equivalent to receiving less than 0.7 mrem/wk. It was also pointed out that different parts of the body can safely take different amounts of radiation. The hands and wrist, it is said, can safely receive a maximum of 19 rem/quarter. Although it wasn't calculated in the article, This is equivalent to about 8 mrem/hr. So, while this article is very dismissive of any risks associated with radium dials, in fact, the figures they give show that if you wear a wrist watch with 12mrem/hr on one hand for 16hrs a day, you are right at the maximum safe exposure for your wrist. In the December 1985 bulletin (vol 27/6 num 239 page 729) there is a third article on the subject. It claims that the math in the second article is wrong. Furthermore, as was pointed out in the first article, some people wear wrist watches 24hrs a day and often sleep with the watch resting against their head. In this case, a dosage of 12 mrem/hr is far in excess of the recommended maximum for the head and eyes. Likewise, pocket watches worn close to the groin or pendant watches worn over the breast would both be of concern.
Another watch collector, redberns, investigated the radium levels on his Hamilton "Whitney". The radiation levels were enough to convince him to have his watch redialed to remove the radium.
Finally, while it doesn't discuss the risks of radium dials much,
there are some interesting pictures of luminous dials at the website
of
Alan's Vintage Watches:
ConclusionsIn summary, I think it can be said that:
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