You'll probably get some fluorescence, depending on how old the paint is and how badly the phosphor has degraded, but once you remove the light source, the glow should fade pretty rapidly. An interesting coda to this is the Rolex GMT Master, which was issued with a bakelite bezel that had radium numerals. Rolex had to recall the watch and replace the bezel thanks to the excessive radiation the bezel emitted, and original bezel watches are therefore extremely rare.
However, if the bezel is original it's basically just as radioactive as the day the watch was made — an important caution for any collector who owns one. It became manifestly clear in the decades subsequent to the invention of radium paint in that the stuff was simply too hazardous for general use, and so the search for substitutes was on. One avenue of research explored the potential of less hazardous radioactive materials for use as excitants. Promethium emits only beta particles, and at a lower energy than radium, so it's generally considered much safer; it also doesn't cause phosphors to break down nearly as quickly.
Seiko is one manufacturer that used promethium as an excitant; the half-life of promethium is only 2. Tritium, like promethium, is a low energy beta emitter; unlike promethium it has a much longer half-life — Tritium is a radioactive form of hydrogen, and tritium gas-filled fluorescent tubes are used not only in watches, but also on everything from cockpit instruments to gunsights.
Two of the best known users of tritium gas tubes for watch dials are Ball and Luminox. Tritium paint for watch dials and hands will lose its ability to photoluminesce over time, although as with promethium, degradation of the phosphor will take place more slowly, as tritium is a much weaker radiation source. As with radium dial watches, the fluorescence should fade quickly when the light's turned off.
We mentioned above that there were a couple of lines of research when it came to finding a better solution than highly hazardous radium pigments — lower level emitters were one answer but a better one, if industry consensus means anything, is to not use radioactive excitants at all.
To get away with this, you need a phosphor that will glow enthusiastically for hours after exposure to light — something that will act as a sort of "light bank," emitting stored energy in a measured fashion. Enter Luminova. Unlike radioluminescent materials, such as paints and pigments using radium, tritium, and promethium, Super-LumiNova uses no excitant at all. Instead, it incorporates a material known as strontium aluminate, which is an extremely efficient phosphor that once charged, will glow very brightly initially, and with diminishing intensity for several hours thereafter.
For strontium aluminate to be an effective phosphor, it must be combined with europium, a non-toxic, non-radioactive chemical element. Strontium aluminate is a much more efficient phosphor than zinc sulfide — it's about ten times as bright and glows about ten times longer and the color can vary between various shades of green and blue, with blue supposedly producing the longest glow time, and green offering better brightness. A major challenge in dive watches back in the day was their readability in the darkness underwater.
Radiomir paint created thereof was among the brightest-glowing lumes at the time. The patented substance subsequently led to an entire collection being named after it. Eventually when all radium-based luminescent substances were found to be highly radioactive and very likely to cause lifelong diseases and ailments on exposure, even Radiomir stopped using radium. When Panerai watches became available to the public, the signature Radiomir design template continued, as it does to this day, but with no radium on it.
This is one of the first few Radiomir watches developed with radium as the base for the luminescent material. The contemporary Radiomir watches take the name forward, but have no radium.
This Radiomir California edition is a perfect example of how the essence of the design remains. Clearly, radium was a bad idea for many reasons.
Women in watch factories in the United States in the early s were known to have contracted serious radiation poisoning from painting watch dials with radium paint. In light of the hazardous nature of radium, the search was on for less dangerous substances. Promethium was one option. It is radioactive, but emits only beta particles and has a half-life of less than three years. Seiko were known to have used promethium, but owing to its limited half-life, its glow would fade away rather quickly.
Tritium, however, with its low beta emission and a Tritium was also used by Panerai in their new patented luminescent substance called Luminor, after which their famed Luminor collection is named. The tritium-based Luminor was patented by them in , and its development inspired the now iconic Luminor case design and collection. However, they discontinued the use of tritium itself eventually. In the late 90s, tritium was in fact banned. And tritium-based substances ceased to be used by Omega in , and Rolex in As with the Radiomir, the Luminor too originally had radioactive lume, as was the case with this early Luminor watch from This modern-day Luminor retains the now-iconic crown protector and cushion-shaped case.
It features Panerai's most recognisable silhouette, and thankfully isn't radioactive anymore. Today, tritium is used again by a few manufacturers, however, not as a paint or paste. A radioactive form of hydrogen, tritium gas is filled into borosilicate glass capsules, internally coated with a layer of phosphor. As the gas undergoes beta decay, the electrons released cause the phosphor to glow. The gas is still radioactive, but is apparently less of a hazard than tritium-based paints, because of being in tubes.
Luminox and Ball are among the watch manufacturers known to use tritium gas tubes quite prominently on their dials. The advantage is that unlike Super-LumiNova, which will most certainly stop glowing after a few hours of exposure to light, tritium tubes will continue to luminesce, even if the glow becomes dull over the years, and lead to them needing replacement. Ball watches use tritium for their luminescence, but only in the form of tritium gas tubes, which minimises the risk of exposure.
The tubes are seen here as hour markers and on the hands. Fireflies use an enzyme called luciferase and a substrate called luciferin to do it. Your watch does it by using electricity from an on-board battery to excite - most likely - a semiconductor, like an LED to produce light.
Good info. Okay next: do companies still use radium to effect a light reaction? I think the article said some are still made I'd rather have my son wear ultra-safe materials on his wrist if possible. So what are the chances a company Chinese in this case still uses radium or any other element I'd rather avoid?
Is there a way to find out? Probably not. For a start, radium is universally acknowledged to be a risky substance to work with, even in places like China, where health and safety is often an after thought. There are strict controls on the production, movement and use of radioactive materials, so sourcing radium for an application like watch paint is likely to be preclusively tricky. Tritium is used brands like Rolex use it , because it's regarded as safer; the half life is - unfortunately - shorter, meaning that the watch face needs a refresh every decade or so The half life of tritium is 12 years, but that just means your beta radiation gets halved, and the intensity of the glow will be halved too.
But that will not necessarily be weak enough to not see anything in dark. I have a watch with tritium markings for over 17 years, it is still gets lit enough to read in total darkness.
Of course I don't exactly remember the initial brightness, but it is still quite readable. Skip to main content. Earth Science. Articles Answers to Science Questions Are glow-in-the-dark watches a radiation hazard? Are glow-in-the-dark watches a radiation hazard? Are Glow-in-the-Dark watches a radiation hazard? Should you store your best timepiece in a lead lined box? Part of the show Why do we Stop Noticing Smells? Public Domain.
Play Download. Question I was just wondering, is there any radiation that would come from a glow-in-the-dark watch that would be harmful to the wearer? Previous Could viruses be engineered to attack cancer cells selectively? Next How quickly can a person exsanguinate from a cut artery? Related Content Science Features. Nuclear clock could help blind people, autonomous cars navigate. Chemistry History. Planet Earth Online - Carbon Dating. By this time, the material starts emitting the photon, which we see by our naked eye as visible light.
Fluorescence - Fluorescent materials emit absorbed energy very rapidly. They will continuously glow if there is a light source, but the emission of particles occurs on mere nanoseconds. Hence, most of these materials will go dark right away once the light source becomes unavailable. For watch dials, using fluorescent materials is not always viable. Phosphorescence — Phosphorescent materials also absorb photons from a light source. The only difference is that they emit those photons as light very slowly, which is why phosphorescent paints are usually used for watch dials.
This material is self-luminous, only when freshly applied. There is no need for an external energy source because there is already light emitted from the radium particles' radiation in the paint.
Back in the old days, some watches had numbers and indexes with radium paint. However, given its dangerous effects in health, it is not almost used today in the modern watchmaking industry. Due to the harmful effects of radium paint, promethium and tritium were later discovered as substitutes.
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