Many people have asked me the same question repeatedly: is the luminous material on watches safe? There is no definite answer to this question as it all depends on the material used for the luminous layer. Most of the watches available today use Super-LumiNova, based on non-radioactive and non-toxic photoluminescent or afterglow pigments. However, it wasn’t always like that…
Panerai made the first luminous watches for the Italian Navy. One of the owners of this Italian company, Guido Panerai, started the first experiments with luminous materials in 1910, and developed the system that was using a mix of zinc sulphide and radium bromide. The process was patented in 1915, and the iconic Radiomir watch was born. The Radiomir and Luminor watches take their names from two luminous substances.
In those days, people were almost completely unaware that Radium is one of the most radioactive elements. The material was used not only for the self-luminous paints for watches, but also for the nuclear panels, aircraft switches, clocks, and instrument dials. This element is a million times more radioactive than uranium, and it takes 1602 years before it decays.
The Nobel Prize winner, physicist and chemist Marie Curie discovered radium initially. This Polish-born French scientist was also the first female professor at the University of Paris, and the first person honored with two Nobel Prizes. Unfortunately, this great woman died from aplastic anemia, which is tightly connected with the exposure to radiation. Even her papers from 1890s are still considered too dangerous to handle, because of their levels of radioactivity.
The very same fate awaited the many who have worked in the watch industry. At the time when Guido Panerai started using luminous paint on Radiomir watches, the dials were painted by hand, using the camel haired paintbrushes. Workers often used their tongue to sharpen the brush, exposing their body to the deadly substance that deposits in the bones, converts into calcium and finally replaces the bone marrow.
Perhaps the best known case of radium poisoning is the story about Radium Girls. This was a group of female factory workers who painted watch dials at the United States Radium factory in Orange, New Jersey around 1917. They ingested large amounts of radium by licking their paintbrushes since no warning about radium toxicity was ever given to the workers. Moreover, the girls thought the Undark glowing paint was “fun”, and they often painted their nails, teeth and faces with the deadly substance. It is estimated that 4,000 workers were hired by corporations in the U.S. and Canada to paint watch faces with radium, earning about a penny and a half per dial. Five of the women challenged their employer in a court case. The media sensation surrounding the case triggered the enactment of regulations governing labor safety standards.
The radium paint is a mix of zinc sulfide and radium. The zinc sulfide emits light when struck by the radioactive particles. Over the years, the zinc sulfide will wear off, and the watch will lose its radiant glow. However, the paint will remain dangerous for no less than 1602 years, which is the half-life of radium isotopes.
By 1930, all dial painters stopped pointing their brushes by mouth, although the Radioluminescent material continued to be used until the late 1950s, when it was replaced by Tritium. In 1946, Panerai patented Luminor, the luminous substance based on tritium, which replaced the previous Radiomir mix developed between 1910 and 1915. Tritium is also potentially toxic since it uses radioactive particles of tritium, which is a low energy beta emitter, to light up the phosphorus layer. The beta particles cannot penetrate the skin but tritium can also be hazardous when inhaled or ingested via food or water. The substance, however, has a short half-life in the human body, of seven to 14 days.
If you own a vintage watch with applied luminescent paint, which are still very expensive collector’s pieces, do not forget that it might be radioactive. The old watches do not have a warning label to indicate radioactivity and radioactive materials. Do not try to take the paint off, and expose yourself to the radioactive dust. The watches using radium are usually marked with “R” or “Ra”. Watches that used tritium usually have two small “T”s on the bottom of the dials by the 6 or have “T<25″ labels. Very old watches do not have any kind of marking to indicate the type of luminous paint used in production of the dial.
In the 1960s, LumiNova finally replaced both of the previously used materials. These new glow-in-the-dark pigments are based on strontium oxide aluminate chemistry and completely safe. LumiNova will stay bright through a single night if it has been subjected to enough light during the day. About 30 minutes are usually enough to reach its full charge. All major watch brands use exclusively Swiss Super-LumiNova, which offers full high-performance over a lifetime of the watch.
Recently introduced self-powered micro gas lights (3H) Swiss technology safely captures tritium gas in a mineral glass tube coated with luminescent material. The Ball is a company behind this innovative 3H Swiss laser technology. These micro gaslights glow up to 100 times brighter than luminous paints for up to 25 years, and do not require charging from any outside light source. But what if the tubes break? Wouldn’t that expose the wearer to the dangerous tritium? To my surprise, there is no radiation risk when wearing 3H equipped watch. According to the precise Swiss testing, even if all 3H tubes were to break simultaneously, the estimated radiation dosage would be 30,000 times lower than the average natural background radiation.