The problem of the luminescence of the indexes and spheres of a watch has held the ground for decades and is still a very well-finished and developed aspect within the watch industry.
In fact, several systems have been used over the years, but all of them involved problems of some kind.
The first and historically most widespread consisted in coupling, in the same luminescent paste, two components: one, called “Scintillatrice” which emits light energy if subjected to physical and / or chemical excitation (thermal, luminous, radiation stress …) and the other, called “Isotope” consisting of a radioactive element.
Radio was one of the first used, but it is much more radioactive than necessary and has been abandoned since about 50 years ago.
Radium is the chemical element with atomic number 88. Its symbol is Ra. Its name derives from the fact that it is one of the most radioactive elements known.
White in color, it blackens on exposure to air. It is an alkaline earth metal present in trace amounts in uranium ores. Its most stable isotope, 226Ra, has a half-life of 1602 years and decays into radon. Surely the best known practical application of this element is the watchmaking field.
Used in the past in luminescent paints for dials and hands of watches, alarm clocks and various instruments. Over 100 ex-clock hand painters, who used their lips to tip the brush, died from radiation: shortly thereafter, the harmful effects of radiation began to be publicized. Radio was used in alarm clock dials until the 1950s. Objects painted with radium paint can still be dangerous today and must be handled with due caution.
Then Promethium, Tritium etc. were used. much less radioactive and with much shorter decay time.
The low-energy beta radiation emitted by the decay of tritium cannot penetrate human skin and therefore tritium is only harmful if ingested or inhaled. Furthermore, its low energy makes it difficult to detect.
Tritium is a “version” of the hydrogen atom, “added” with a couple of electrons.
This makes it more “nervous” than normal hydrogen and therefore radioactive.
However, while in the case of Radium, of the two components, the first to “give up”, that is to age and cease its functions was the scintillator, which was literally “burned” by the Isotope, in the case of Promethium and Tritium they were the isotopes to cease to be radioactive, due to their much shorter half-life. therefore the problem was: much less radioactivity, but still present in a sensitive way, but rather short duration of the luminous efficacy (between 5 and 12 years).
Their radioactivity, even if enormously lower than the Radio, was therefore considered excessive, if only because it could be avoided.
Promethium and Tritium were destined for abandonment and banning and, therefore, other systems were sought, even more efficient and, above all, less radioactive.
Among these … the so-called “Trasers”, or small crystal vials, very thin, cut and “welded” with the laser, whose internal surface is “smeared” with sparkling substance and filled with gaseous Tritium.
In this way, very little Tritium is used in a gaseous state, therefore very little dangerous and radioactive, furthermore the continuous and efficient contact with the sparkling component guarantees superior efficiency and longer life.
The illumination system of the indices based on vials filled with Tritium vapors was, to a certain extent, the squaring of the circle in matter.
The Traser have been produced, for quite some years now, only by one company, Mb Microtec, for all producers in the world, in different shapes and in many colors: lenses, headbands, rings, tubes etc. red, green, yellow, white, etc …
The company owns the “Traser” brand, which has become the common and commercial name of the vials, and produces the homonymous watches.
Radio or Tritium?
Tritium is often confused with radium, therefore, to be more precise and certain what we are talking about, it is necessary to measure the radioactivity emission of the watch. If it is almost nothing it is Tritium, if instead we speak of Radio the Geiger counter is excited at least ten or twenty times more.
Radium, being much more radioactive, “burns” the sparkling substance and alters its color much more than Tritium.
It will have happened to everyone to see vintage watches with very, very burnished indexes … here, one of the causes of that “burning” is the presence of Radio in the dough, but also an accentuated sensitivity of the sparkling substance to the presence of the Radio. In fact, it is not certain that more “burned” indices are also more radioactive …
The color, both the original and the aged one, are given, in fact, by the luminescent substance, by the scintillator,
and not from the radioactive component, even if commonly, but erroneously, it is said “triziare a dial” or “which is the color of the … Tritium of this or that clock? yellow, white, green, etc …”, but in reality, the color of the tritium is always the same and the chromatic variations derive from various other components of the luminous paste.
the fact that, if subjected to light, especially after a period of total darkness, a luminous clock (whether Tritium or Radio) is still faintly luminous, does not depend at all on radioactivity, which may or may not exist, regardless of this phenomenon, but the conditions of the scintillator. The scintillator emits brightness when stimulated, until it is neutralized by the radioactive component, very aggressive. It can emit it if stimulated by heat, light or radioactivity.
Therefore, the erroneous belief according to that “if it is no longer luminous, it is no longer radioactive” or vice versa, or the equally erroneous one, according to which “if it is still luminous it is Tritium and not Radio” and vice versa … they are nonsense supported by those who do not know what they are talking about …
the color of the luminous paste, the way in which it “changes” with age, etc … depend on various factors, but they are all linked to the scintillating substance and not to the isotope: it is the scintillating substance that is luminous, colored, that changes by turning color, etc … Normally the factors that cause colors to change are environmental: radioactivity itself, humidity, sunlight (UV rays), the quality of the pigment used, sometimes even the type of lubricants used for the mechanics which, evaporating, form gases inside the box.
APPENDIX: THE VINTAGE PANERAI
Many have written to me asking about vintage Panerai.
It being understood that what is written above remains valid, Panerai first of all used Radio and not Tritium. Radium is a much more radioactive isotope.
Just to understand … it is more radioactive than Uranium and has a half-life of about 1600 years … Moreover, Radio is used in a solid state.
Panerai used sandwiched, layered dials, for which a large quantity of luminous compound was enclosed in a round, discoidal box, on which the numbers were milled … A lot of brightness, it’s true … but also a lot of radioactivity for the next 4500 years … Obviously I’m talking about the first Radiomir: Panerai itself realized how dangerous it was and ran for cover as soon as it was technically possible.
The Radiomirs mount a dial with a huge amount of Radio 226 and Radio 228. Which remains radioactive for over 1600 years !!!
Just because it’s not brighter doesn’t mean it’s not radioactive! Indeed, in many measurements made with semi / professional instruments, it was not possible to establish how radioactive the old Radiomir are … as the radioactivity exceeded the maximum values indicated in the scale of the Geiger counter used.
The conservation of these must be very careful and done with suitable equipment. Obviously, only some historic Panerai are radioactive and in any case can be reclaimed. Those on display in Florence were.
Not everyone knows that the operators of the Navy sank their Radiomir, including straps and various spare parts, in a box full of concrete, because the son of the non-commissioned officer who kept them, in his accommodation, fell ill with leukemia … very brave people, who manipulated explosives and faced very dangerous ways of working and diving, realized that the useless risks remained unworthy of being faced …
all the women who assembled the dials died of cancer in the mouth or throat, because they used to lick their finger or brush to make the spheres adhere better and then mount them.
What about the tritium index aging? Sometimes the changing color of them is not uniform and seems like the watch has been touched or some indexes have been replaced with different materials. Is this true? No, and let’s understand why.
In a forum concerned to this issue this conversation took in place:
I generally devour the discussions of the Rolex Vintage section which are often interesting and stimulating and I often read phrases when estimating vintage models such as: “the spheres have been replaced as they are of different shades compared to the buckshot / shot glasses!”.Question
I don’t doubt that “often” is really the case, but there are some exceptions.
I have always been the owner of a 14060. He has been following me for almost 22 years and is undergoing a slow, but constant change in the trices of the glasses only!
The hands are exactly as they were in ’92 when the watch came out of the dealership, while the rest are taking on a honey hue. I assure you that nothing has ever been replaced! In this case, if I were no longer certain that no one has ever put their hands on it, many of you and I would have doubts about the coevity of my Sub. I say this because there is a risk of retreating to restore originality / coevity or to obtain a harmony of tones when in reality it is all the result of the passage of time. As usual, the photos are ugly, but you certainly appreciate the dystonia between spheres and glasses.
From what I know, Rolex sometimes used different suppliers for dials and hands or even inventories …
Therefore, the chemical composition of tritium, being different, can take on different colors over time.
So it may happen that the hands, even if never replaced, may have a different shade from the indexes.
Other reasons honestly do not come to mind …
If this bothers you, you can have them restarted (which is quite simple) to make them the same as the color of the index fingers.
These differences in the color change of the tritium between spheres and indices are normal and are by no means an indicator of the replacement of the spheres. Among other things, it is a peculiarity almost always present on specimens produced in the late 80s (5513 small glass indexes for example) and in the early 90s.
Most likely, as the forumist who spoke earlier wrote, this is due to the fact that Rolex sometimes used different suppliers for dials and hands, whose material underwent different color changes over the years.