Luminous Paint on Watch Dials and HandsCopyright © Notice
Radioactive Luminous Paint
Some vintage watches, especially military watches, had the numerals and hands made luminous or "glow in the dark" by painting them with "radioluminescent" paint where the glow from the paint is caused by nuclear radiation. This paint was not like the luminous compounds commonly used in todays watches, most of which charge up in sunlight and lose their glow over a few hours. The luminous paint used on WW1 era watches was made with a mixture of radioactive radium and zinc sulphide. The zinc sulphide glowed brightly when hit by radiation from the radium. This paint glowed all the time, day and night, without needing exposure to sunlight, and continued to glow for years on end, even when stored away from the light in a drawer. However, after some time, maybe twenty to fifty years, the zinc sulfide no longer glows in the dark - but the radium has hardly changed and is still there, emitting radiation.
Luminous radium paint on dials was first used around 1910, before the dangers of radioactivity were fully understood. Although health problems in workers using radium paints were noticed in the late 1920s, radium paint continued to be used up until about 1950. There wasn't a suitable safer substitute available, and military authorities continued to specify radium based paint for important applications such as compasses, instruments, gun sights, and, of course, watches.
Air Publication 112G-0815-1 July 1966
Although the dangers of radium luminous paint had been identified by the 1950s and alternative luminous compunds were being used or developed, the use of radium based luminous paint didn't stop overnight. There was nothing else that gave such a bright and lasting glow in the dark effect, there isn't anything even today that compares to the the brightness of luminous radium paint. Radioactive luminous paint continued to be used for some applications, and of course watches and other items such as alarm clocks and aircraft instruments manufactured in earlier times continued to be used. The picture here shows a warning in an Air Publication British military standard issued to the Navy and Royal Air Force in July 1966.
If your watch was made before 1960, and has thick paint, often even gungy looking in WW1 era watches, often yellowish brown on WW1 era and green on later watches, on the hands and numerals, and the hands and numerals are designed to carry a large area of paint rather than thin brush strokes, then the likelihood is that the original paint was made with radium, even if it no longer glows in the dark at all.
Modern Luminous Compounds
Modern luminous compounds are safe and fall into two categories.
- Light charged compounds
- "Safe" radioactive compounds
The first category, light charged or "afterglow" luminous paints charge up in sunlight, and in artificial light to a lesser degree, storing ultraviolet light energy like a battery and then releasing it as visible light in the dark. (The release of visible light also happens in daylight, you just can't see it.) These paints tend to initially glow in the dark very brightly, but the bright glow soon fades. Super-LumiNova is probably the best known of this group of compounds, which also includes Luminova and Lumibrite.
The second category, safe radioactive compounds, is very similar in principle to radium based paint but uses radioactive materials such as tritium gas contained in small glass containers. Tritium gives off beta radiation which cannot leave the glass container and is far less dangerous than the gamma radiation given off by radium. Watches with tritium luminous compounds glow all the time, like radium compounds, and do not need charging up in sunlight, but are safe as long as the glass container is not broken. If you are unfortunate enough to break a container of tritium, just stand clear and let it disperse into the atmosphere, opening widows and doors if necessary. This is also quite safe, there is always a small amount of naturally occurring tritium in the atmosphere escaping from natural sources in the ground, which is where the tritium in your watch came from in the first place.
Watch with radioactive luminous paint
Radium Luminous Paint
The half-life of radium is about 1,600 years, so over the 100 or so years since a watch dial was painted with luminous paint, the radium activity will have decayed about 4%, about 1% for every 25 years. This means that paint that was made with radium 100 years ago will still be 96% as radioactive today as the day it was made. Radium and its fission decay products (such as radon gas) have the potential to cause various health risks, and therefore watches with radium paint should be handled carefully and in ways to minimize these risks. The danger is not so much from radiation received from the watch when wearing or being near to it, but more from inhalation or ingestion of paint particles or contaminated dust.
Why doesn't old radium paint glow in the dark? You can't see radiation, and radium paint only glowed because the radioactive radium was mixed with a fluorescent compound, usually based on zinc sulfide. Radiation from the radium would hit the zinc sulphide, which would emit light in response. Over time the fluorescence property of the zinc sulfide was worn out by the radiation, and that is why the paint no longer glows in the dark. The radium is still there, almost as active as the day the paint was mixed, but the fluorescent compound no longers gives off light when it is hit by radiation.
Radium and its decay products, the things it breaks down into (and the things that those things also break down into) are alpha, beta and gamma emitters. Alpha particles are composed of two neutrons and two protons, the same as the nucleus of a helium atom. This means that they are (relatively) large and slow moving, and have a positive charge. They can be stopped by a few inches of air or by the surface layers of your skin or, more importantly, the case or crystal of your watch. However, if flakes of radium paint are inhaled they can sit in the lungs, where the alpha radiation can hit the delicate (much more delicate than skin) internal tissue of the lungs and cause tumours. Beta particles are electrons which will also be stopped by the watch case or crystal. Gamma rays are electromagnetic radiation, like light or X-rays, but with higher energy. They will easily pass through the case of a watch.
There is no need to panic if you realise you have watch with radium paint. The watch that I describe testing with a radiation detector below is a 1918 World War 1 era watch, and whoever painted the luminous paint on the hands and dial seems to have applied a good thick coating, and the paint seems to have been particularly radioactive. I guess that at the time they just wanted a really good glow in the dark, and didn't appreciate the dangers. Later watches that I have tested since have much less paint on the hands and numerals, and are a lot less radioactive. I have a later watch from the 1920s, still in a Borgel case like the first one I tested, but the paint is a lot finer in application, rather than the big daubs on the first watch, and perhaps incorporates less radium - after all, it was an expensive substance. This second watch with the finer paint registers much lower on the radiation detector, and I wouldn't be anything like as concerned in wearing it.
Any watch with radium paint on the dial I regard as reasonably safe to wear on a once-in-a-while basis, and perhaps more regularly than that if the paint has been finely applied, unlike the watch pictured on this page. But to minimise risks it would still be sensible to not wear it all the time, and certainly don't sleep wearing it, or keep it on your bedside table. The much more significant danger occurs when opening or working on such a watch, and I am particularly careful not to breathe in any of the paint or its dust, or to spread bits of the paint around, contaminating my workspace.
Further information for persons working with watches that have this type of luminous paint is available on the HSE web site in the article NEW CONTROLS INTRODUCED ON TIMEPIECES CONTAINING RADIOACTIVE SUBSTANCES which you can get to by clicking on the link. This article states "Up until now those in the retail and antique trade have been free to dispose of damaged clocks and watches luminised with radioactive material, that are beyond repair, in the dustbin with other general refuse. Today because of a change in legislation made necessary by the Basic Safety Standards Directive (96/29/EURATOM) the situation has changed ... and you may be required, in certain circumstances, to seek Environment Agency approval under the Radioactive Substances Act 1993 (RSA 93) before disposing of such timepieces. Those circumstances are:
- if the timepiece is not made to international standards (which govern the use of radioactive substances at the time of manufacture); or
- if more than 5 timepieces, which meet international standards, are to be disposed of."
When watches were made with radium paint during the first half of the twentieth century there were no international standards governing the use of radioactive substances, these all seem to be modern (post 1950s) standards governing the use of tritium and promethium compounds. This would mean that all watches with radium paint fall into the first of the two categories listed and would need approval for disposal. The legislation goes on to say "A major implication of this change in the law is that those in the retail and antique trade will now need to know what radioactive substances are on their premises and in what quantity." However, it finishes with a final get-out clause "Please note this legislation does not apply to private individuals with a related horological hobby/collection."
Testing Luminous Paint for Radioactivity
If you think your watch has luminous paint on the hands and numerals, the first easy test is to keep it in the dark overnight and examine it while still in the dark. Then expose it to sunlight and take it into a dark room. If it was dark after being kept in the dark overnight, and then charged up in the sunlight and glows brightly in the dark, it has a modern "light charged" luminous compound and is quite safe. Although zinc sulphide will charge up in sunlight and then glow in the dark, old radiation damaged zinc sulphide exhibits very little response to sunlight and its characteristics are very different to modern luminous paint. If the zinc suplhide doesn't glow in the dark due to radium radioactivity, but does glow when charged up by sunlight, then logic says there isn't any radium present.
However, if the paint remains dark at all times, then it may have radium paint. If it does glow faintly in the dark but doesn't charge up in sunlight, then it almost certainly has radium paint.
I bought a radiation detector so that I can test my own watches for radium based luminous paint. I am glad that I did - the first watch that I tried it on, the same black dial trench watch with plenty of luminous paint left on the dial, gave a strong reading as you can see below. I now offer a service to test your watch for radiation, including a certificate stating what I find. This would be useful for your own peace of mind, or if you are thinking of selling your watch, especially if you have had the dial repainted to remove the radium. If you are interested in this service (you probably need to be in the UK, where I am) then please drop me a line at Please don't give out my email address, refer anyone interested to this web site. I try to answer all emails I receive so if you don't get a reply in a few days please check your junk or spam folders.
The first picture shows the radiation detector reading 0.14 micro sievert per hour background level, which is pretty normal, and the alarm level set by the factory at 0.3 micro sievert per hour (µSv/hr). The manual says that levels above 0.2 µSv/hr above background radiation need investigating and either clean up or evacuation, so with background at 0.14 µSv/hr the alarm level of 0.3 µSv/hr is just below the level at which action is required.
The second picture shows the effect of putting the watch next to the detector: the level jumps to 1.92 micro sievert per hour and the audible alarm goes beserk. In the manual accompanying the detector, it says ". . . if a dose rate of more than 1.20 micro sievert per hour is displayed, it is necessary to leave the zone urgently . . ." Although this warning refers to radiation levels which affect a whole area, rather than from a point source such as a watch where the intensity of the radiation experienced can be diminished by simply moving away from the watch, it does show that the amount of radiation given off by the watch is more than 10 times the naturally occurring background radiation and should not be simply ignored.
So What Do These "Sievert" Things Mean?
In the 1980s when I was working on building nuclear power stations I was a "Certified Radiation Worker" or some such thing, qualified for "hot temperature conditions", which meant that I was "allowed" to receive as part of my work an annual radiation dose of up to 5 rem, 20 times what was allowed for the general public to be exposed to. (In fact, I probably got more dose from the chest x-ray I had as part of my annual radiation worker's medical tests than I did in work.) I am used to talking in rems so the modern Sievert units leave me a bit in the dark, but I decided I needed to get up to speed and get familiar with the new units that my radiation detector uses, so here goes:
The impact of ionising radiation is measured as energy absorbed in body tissue in units of "gray". Exposure to different types of radiation does not produce equal biological effects, so when discussing radiation effects an equalising unit called a rem (Roentgen equivalent man), or now a Sievert (Sv) is used. Regardless of the type of radiation, one rem or sievert of radiation received produces the same biological effect. One sievert equals 100 rem, so my allowed exposure that used to be 5 rem per year would now be called 50 millisieverts per year (mSv/yr) (although I notice they have now reduced the allowed exposure for nuclear workers to 20 mSv/yr, or 2 rem/yr.)
In the UK, the legal limit for radiation exposure from sources such as nuclear plants for members of the public is 1 mSv a year. The "background radiation", the natural radiation that we are all exposed to is reckoned to be about 2 mSv per year, some of which comes from natural sources in the ground and in rocks, and some from cosmic radiation. Flying exposes you to more cosmic radiation and an airline crew flying the New York to Tokyo polar route are estimated to receive an annual exposure of 9 mSv per year because of this. A steady dose rate that gave an exposure of 1 mSv/yr would be about 0.1 micro sievert per hour (µSv/hr), 10 mSv/yr would be about 1 µSv/hr. The instruction manual which came with my radiation detector says that "defensive measures" (it's translated directly from Russian) should be employed if the measured radiation level in a room exceeds the external background level by 0.2 µSv/hr or more, which would correspond to 1.75 mSv/yr.
The background reading I measured away from the watch above of 0.14 µSv/hr would be 1.22 mSv/yr, which is below the usually quoted "typical" background radiation. The elevated level next to the watch of 1.92 micro sievert per hour works out at 16.8 mSv/yr, or about 10 times background radiation. This will all be gamma radiation escaping through the case or crystal of the watch. So this is the level of radiation someone wearing the watch would be exposed to. Obviously it's not "whole body" radiation, which the limits I discussed above are based on, but it is higher than I would want to be continuously exposed to.
I didn't measure the radiation level of the watch above with the dial out of the case. However, next is one I worked on recently.
Radioactive Watch No. 2
When it arrived it was in a zip lock bag, and the crystal was missing. I could see that the paint was the original radium paint so I decided to see what I was dealing with before I took it out of the bag. As you can see, I got a reading of over 5 µSv/hr. This rather surprised me because it was a lot higher than I had seen with the watch I described above, and this one seemed to have less paint remaining than that one. The higher reading may have been due to beta radiation that would have been stopped by the crystal but which could pass through the zip lock bag. I decided to remove the hands and dial, working on disposable paper towels and wearing a dust mask.
The next picture shows the dial and hands next to the radiation meter and, as you can see, it has gone off scale, so the radiation from the dial and hands is over 9.99 µSv/hr. I don't know how much over, because this is the maximum reading of the meter. As you can also see from this picture, there isn't much of the original radium paint left, just bits on the numbers from 12 to 4 and a bit on the 10 and the hour hand. That this small amount of paint produced so high a reading surprised me.
I then stripped the radium paint off the dial and hands and took some more readings. The dial then gave a reading of 1.47 µSv/hr so I guess I didn't quite get rid off all the paint.
I tested the movement after I had removed the dial, and also the case, before I did anything to them. I got a reading of 0.64 µSv/hr off the movement and 0.43 µSv/hr off the case.
Why were the movement and case showing a reading after I had removed the dial? It seems that one of the fission products of radium is radon gas, which can obviously move around inside the watch and, after a few days, itself fissions into solid materials. These are also radioactive and settle as dust on the watch movement and case. Obviously this dust is quite mobile so you need to be careful not to spread it around and contaminate your workspace.
I have now discussed this whole matter with the NRPB. The view of the person that I spoke to was that the dose of radiation that would be received from working on a watch like this for a short time was low enough to not be a concern. A dose rate of say 10 µSv/hr would take 100 hours to accumulate the 1 mSv allowed to members of the public from nuclear power plants, and 200 hours to equal background radiation. And this is not a whole body dose, which those figures are for. However, when working on a watch one is very close to it, and the eyes and fingers would be most exposed. Wearing an eyeglass or similar would protect the eyes from alpha and beta radiation, but would not stop the gamma.
The figure of 10 µSv/hr was rather plucked from the air because my radiation detector had gone off-scale at 9.99 µSv/hr. The issue of "Radiation Protection News" that I linked to above also has a section about vintage aircraft which notes that many aircraft built before circa 1950 have instrument dials luminised with radium paint. Dose rates on contact with these instruments can sometimes exceed 200 µSv/hr and dose rates in the pilot's position may be as high as 15 µSv/hr. The note goes on to give guidance that where dose rates in excess of 2.5 µSv/hr exist, steps should be taken to reduce radiation levels and/or prohibit access by members of the public. On the face of it, the radiation received from a watch would be broadly similar in extent to the radiation received from an aircraft instrument while sitting in the pilot's seat, and remember that 2.5 µSv/hr is less than I measured off the second watch while it was in its zip-lock bag.
The NRPB man was also concerned about removing the paint from the dial and hands, as this could be seen as creating "radioactive waste". The view seemed to be that as far as the authorities are concerned the paint is OK so long as it is on the dial inside the watch case, but that you shouldn't open the timepiece or remove the paint from the dial. The official view seems to be, it's OK to have one of these watches, but don't get too close to it, don't wear it, don't work on it, and don't remove the radioactive paint, but this doesn't apply if you are a private individual with a related horological hobby/collection.
So how do I deal with the residual activity on the case, movement and dial? I put the movement, dial and hands, and case, separately, in a bath of watch rinse solution in an ultrasonic tank to remove as much radioactive dust as possible. Usually this removes virtually all traces of radioactivity so that I feel safe to work on the watch as normal.
Pocket Geiger Smart Radiation Detectors
I bought my radiation detector some time ago and it was quite expensive. However, as a result of the nuclear accident at Fukushima, Japan, an organisation was set up to develop inexpensive radiation detectors for everyone. The resulting product is the Pocket Geiger Smart Radiation Detector, an accessory which is available for both IOS (iPhone, iPad etc.) and Android devices that works with a free downloadable app to display radiation readings on your smart device. The Pocket Geiger is available in several different models and prices from around £40 from Radiation Watch UK. I haven't tried one of these myself yet so this is not a personal endorsement, but it looks like a handy and inexpensive piece of kit for anyone handling old watches with potentially radioactive paint, or even for anyone who is just interested to know how much radiation is in their surroundings. If you get one of these, do let me know how you get on with it.
The Bottom Line
So what's my final position on all of this, I hear you asking. Well, as a private individual with a horological hobby and collection, the rules laid down by the Environment Agency don't apply to me. However, I am conscious that I don't want to take any unneccessary risks with my own health, so I am going to be careful when working on watches luminised with radioactive paint and take the precautions outlined in the "And Finally" section below, and I am not happy about simply sending in any form old luminous material to landfill, so I am going to work with on that too - although I am not quite sure how at the moment. The BHI would appear to be the obvious first place, so I have contacted them.
It doesn't take long to remove the dial from a watch and strip the paint off, and clean the case and movement, so my annual exposure to gamma and beta radiation from this source will be low, and I will try to avoid inhaling or ingesting any radioactive materials by using a mask. I will take the steps I have outlined to keep my workspace free of contamination and I will monitor the levels of radioactivity with my geiger counter.
I will dispose of the residual paint, mask, gloves etc. in the bin, on the basis that this is only the same quantity of material as an unknowing member of the public putting a complete watch in the bin. I am not happy about this and would much rather send the paint to a safe disposal rather than landfill, but the "powers that be" have made the process so costly and complex that this is not possible for me.
If you have any corrections, questions, suggestions, or comments, then please drop me a line at Please don't give out my email address, refer anyone interested to this web site. I try to answer all emails I receive so if you don't get a reply in a few days please check your junk or spam folders.
Repainting Luminous Dials - Some Notes of (aesthetic) Caution
I decided to get the dial of this watch repainted to remove the radium paint. Although I think it is fair to get a dial repainted on a run-of-the-mill watch that you want to wear everyday, historically significant watches should as far as possible be preserved if they are in good condition; but of course most watches fall somewhere in between run-of-the-mill and historically significant. For instance I have one of the first officially issued British military wristwatches from 1917 which I wouldn't even think of having repainted because of its historic importance, but other watches I wouldn't be so bothered about if say a lot of the (brittle) radium paint was already missing. Did you know that at one time the RAF stopped using luminous watch dials because the vibration of the aircraft shook the radium paint off?
Before I wrote this web page I had had an Omega dial restored because most of the radium paint had been lost, and the dial painter has done a very good job in reproducing the thick appearance of the old radium paint, which considerably improved the appearance of the dial and the watch now looks very good. But the watch that is pictured on this page was restored by another company, and they have replaced the old paint with modern luminous light charged paint. I don't have a problem with the use of modern luminous paint, but they haven't reproduced the colour and appearance of the old paint and this has rather spoiled the vintage appearance of the watch. This has caused me to be more cautious in having dials restored.
Modern luminous paint could be considered to be out of place on a WW1 era watch, because it charges up in sunlight and then glows brightly in the dark, shouting out that the worn out radium paint has been replaced with a modern lumious paint. A more accurate restoration would be to use non-luminous paint, because no original WW1 era watch glows in the dark today. But there are good reasons for replacing radioactive paint with modern luminous paint. The old paint is radioactive and so there are good health reasons for replacing it. This should be done carefully, reproducing the colour and texture of the old paint so that the watch retains its vintage appearance. However, if this is done skilfully using a non-luminous paint, how is someone to tell if the watch has new paint instead of old radioactive paint? Not everyone wants to invest in a radiation detector, so using a modern luminous paint, with its distinctive characteristic of charging up in sunlight and then decaying in brightnes in the dark, is a good way to show that the paint has been changed and is safe. And it will also glow in the dark, an effect which everyone likes!
Bear in mind that removing the paint is easy, putting it back to match the original is difficult. I would recommend that you take some close up pictures of the dial and hands and send them to several companies. Give a detailed description of what you want doing and ask them if they can do it in the way that you wish. If you want the dial and hands to look exactly like they do now, paint colour and finish included, make sure you say so. Be as detailed as you can in describing what you want, don't imagine that they will know. Take up references and do your due diligence before committing your dial to them.
I have used a couple of UK based dial repainters, but they tend to be quite expensive. US dial refinishers seem to be cheaper because they have a greater market and therefore are able to work on a larger scale, more commercial basis. A poll on the NAWCC message boards recommended a number of US dial refinishers, with International Dial Co. coming out as the clear winner. Next time I need a dial refinishing I am going to give them a try, and I will record the outcome here. NB: I haven't used International Dial Co. yet, and I don't have any connection with the company, so this is not a personal recommendation from me, I am just going on the results of the NAWCC poll.
If you insist on removing radium paint yourself, then be very careful. I can't give you any "guidelines" for obvious reasons, but here is what I do, just for your information. These are not recommendations, just notes of what I do - I can't and don't take any responsibility for what you do.
When dealing with an old watch with what looks like luminous paint I am always aware that there may be loose flakes of paint under the crystal on the dial, and radioactive dust from radon decay throughout the movement: before I open the watch, or even the packaging that it was delivered in, I think about how I am going to deal with these. I wear a disposable dust mask and disposable latex gloves and work on disposable paper towels. I try to work quickly to minimise my exposure, but without rushing.
To strip the paint from the dial and hands I use a liquid paint stripper and I make sure that the dial and hands remain submerged or covered by the liquid while I am flaking stubborn bits of paint off - the idea is to avoid any dust or tiny flakes of paint becoming airborne. I then wash the movement and case in a bath in an ultrasonic cleaner to remove radioactive radon decay dust before I dismantle the movement.
After I have finished working I dispose of the mask, gloves and the paper towels. I fold them up carefully so that anything on them is contained. I then give the work surface where I was working a good wipe down with a disposable damp cleaning cloth and dispose of that too. And then I check everything with my Geiger counter.
How to dispose of the now-radioactive paint stripper and liquid I cleaned the movement and case with is a concern. I am fairly sure that pouring them down the drain is a not a good idea, but I believe that the quantity of radioactive material from single watch is acceptable to put in the bin for landfill disposal - after all, this is only the same quantity of material as an unknowing member of the public putting a complete watch in the bin. As I said before, I am not happy about this and would rather it was disposed of properly - or even reused, I am sure that radium must still have its uses - but it appears I have no choice other than to put it in the bin.
Let me know if you have any better ideas - legal ones, that is! And remember, these are not my recommendations, they are just thoughts to help you decide what to do - anything you actually do is your own responsibility.