Luminous Radium 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. 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 "fluoresces" (glows 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 fluorescence of the zinc sulfide is worn out by damage caused by the radiation from the radium, so the paint 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.
If your watch was made before 1950, 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.
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%. 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, even if it no longer glows in the dark. Radium and its fission decay products (such as radon-222 gas) have the potential to cause various health risks, and therefore watches with this 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. Radium is an alpha and gamma emitter and if flakes of the paint are inhaled they can sit in the lungs where the alpha radiation can cause tumours.
Modern Luminous Compounds
Modern luminous compounds 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 completely safe.
Safety Considerations for Watches with Radium Paint
There is certainly no need to panic if 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 is 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 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 one should be particularly careful not to breathe in any of the paint or its dust. The best way to make sure that there is no risk is to have the radium based paint removed and replaced by a paint that looks the same but is not radioactive. Naturally this needs to be done by someone who knows what they are doing, so don't try this at home, and see my note of caution below.
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." ... "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." ... "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 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 charges 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 it 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, sent it beserk, 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, please drop me a line at . You shouldn't need to copy the email address, just click on it.
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. 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 radiation hazard from the radium is not negligble, and should not be ignored.
Repainting Luminous Dials - Some Notes of 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 wrist watches 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 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.