Those vintage hour numbers, indices, plots and hands that glow on their own (termed radioluminescent, as opposed to photoluminescent, which requires light to charge)? That might just be radium, and furthermore, it could be enough you should do a bit of research. People accept different levels of risk related to radioactive material, so I can’t tell you whether it is “safe” to wear your watch, or if the radium in your watch can do harm (at the least, make sure the watch stays in one piece and remains closed…though even then, gamma particles can still make their way through crystal and metal).
What is lume/radium
When people refer to lume with radium, they are talking about radium salts mixed with a chemical phosphor, which results in a compound then developed into a luminescent paint. The paint (lume) glows due to mixing, though over time the glow of the paint will fade as the fluorescence of the mixture degrades due to the radium. The radium is still there (and will be for a long, long time… it has a 1,600 (!) year half-life), in amounts nearly as high as when the watch was made, though the compound no longer emits as much light. So don’t think just because your vintage watch doesn’t emit light, it no longer poses a hazard. By the late 1960s, radium was phased out and replaced with much safer alternatives.
How to know if your vintage watch has radioactive material
The easiest and most reliable way to know the level of radioactivity of your watch is to purchase a Geiger counter. Reasonably accurate devices are not inexpensive, starting at the level of the RAXED 1053, for example. Others to check out include the Mazur Instruments PRM-9000 and SOEKS 01M. Another route some collectors and watchmakers to save some dollars is to purchase old military surplus Geiger counters (just make sure you calibrate!).
Outside of going to the trouble of purchasing a Geiger counter, text on your watch dial may provide some information on the level of radioactivity at time of production:
- Swiss: made in Switzerland. If it has luminous markers, and made prior to the 1960s, then the watch most likely has radium. After 1998, watches may have Swiss or Swiss Made on the dial, however by this time LumiNova was used instead of radium.
- T: indicates that tritium was used, as opposed to radium. Tritium, introduced in the early 1960s, had replaced radium (Radium-226) in watches largely by the end of the 1960s, and although still radioactive and potentially hazardous, the beta particles are not able to escape through the watch glass or skin (but it is a health threat if ingested). Both tritium (H-3, half-life of 12.3 years) and promethium (Pm-147, 2.6 year half-life) are radionuclides, but emit much lower levels of radiation than radium (Ra-226). With promethium’s relatively short useful life span, it was replaced by tritium.
With the introduction of tritium came new markings on the dial, with “T” added to watch dials circa 1963. Tritium was used until 1998.
- R: at the same time “T” was added, dials “R” or “Ra” were added, indicating radium [9]
- Swiss T: a watch that is Swiss made, and with less than 5.0 mCi (mCi is a millicurie, a unit of measuring radioactivity).
- T Swiss T: Swiss made, contains tritium and emits less than 7.5 mCi [10]
- Swiss T<25: Swiss made, contains tritium and emits less than 25.0 mCi [10]
- Pm: contains promethium (may be designated by P, Pm, or Pm 0.5) [10]
- L Swiss L: optional marking indicating that the lume is photoluminescent (due to exciting the luminous radiation, as opposed to radioluminescent, which is due to the radioactivity of the material) [10]
- Rolex (and Tudor) timepieces will have additional symbols to indicate different levels of radium. The “exclamation point”, where a small dot is below the index marker at 6 o’clock (first seen in 1962), indicates that the piece is following Atomic Energy Commission regulations from 1960 and has lower radiation levels. The underline on the dial (seen starting in 1963) was used to indicate still lower radiation levels, in line with <25 millicuries of tritium. [11]
- Optional markings: The ISO standard governing dial marking (ISO 3157: Radioluminescence for time measurement instruments — Specifications), which limits material to tritium and promethium, doesn’t require any marks/marketing if there is less than a certain level of radiation in the watch [10]. These dials may optionally be marked with T or Pm.
- Symbols: military watches have markings that designate levels of radiation, such as Circle T, Red Circle 3H, H3 and radiation symbol (required starting in 1975 to indicate tritium) [12], Yellow Circle with Red Triangle Nuclear mark, and Triangle Nuclear mark.
- σ T SWISS T σ : does not indicate radioactivity, but rather was used for a period of time to signify that the markers and/or dials are made of gold (white or yellow), and a designation selected by members of APRIOR, the “Association pour la Promotion Industrielle de l’ Or”, an industry association for those making gold watches. This designation was mostly used around 1970.
[9] http://forums.watchuseek.com/f11/gruen-precision-day-date-ra-swiss-ra-dial-2907322.html
[10] http://www.watchfreeks.com/33-general-watch-discussions/936-what-does-t-swiss-made-t-mean-dial.html
[11] http://rolexpassionreport.com/316/the-rolex-exclamation-mark/
[12] http://olive-drab.com/od_soldiers_gear_watch_46374.php