Trying to learn more about lume and what information it could provide about the history of a watch. From what I have read (from posts such as by ConElPueblo - thanks!) I suspect there aren't any hard and fast answers, but if the lume (here just talking about radium and tritium) is a certain color, does it tell you anything with some certainty...or at least incline you to guess at why the change? Such as if the lume is more tan, brown, orange, yellow, green/mint green, black, hints of red... I suspect some lume colr, such as if mossy green or black, is most certainly due to moisture/humidity entering the case. Are there other specific changes that occur simply because of sunlight? Can simply the aging of the lume (and maybe even the batch of lume depending on the manufacturer of the watch) cause it to change color radically? And say, even left in a safe or desk drawer? Separately, why would hand lume discolor differently than lume on a dial (assuming no relume, of course)? Thanks all!
I suspect there are several factors, as you say, not the least the precise lume chemistry i.e. why does the lume on certain 2998 speedmasters go that orange-brown colour? Or maybe that colour occurs due to some reaction (off gassing?) between dial paint and lume, off gassing of lubricant reacting with lume.......who knows. Yes, that mossy green look you describe is often associated with diving watches thus indicating it is moisture related. The frequently quoted reason for hand lume being a different colour to the dial lume is that the hand lume is exposed on both sides, whereas the dial lume is only exposed on the one side. An intriguing subject!
@andomegas Without a controlled situation wherein the watch owner knows (at all times) the environmental conditions under which their timepiece has been placed (for the life of the watch), and therefor can attribute any lume transformation/degradation to that specific environmental condition, then it is not possible to say with a high degree of certainty that “this color-type means X happened to the watch.” The only thing that approaches any certitude related to a specific lume coloration would be a water damage event; there are consistent formal characteristics of radium and tritium material having undergone moisture intrusion that can be recognized, across brand types. Generally speaking, tritium will turn a creamy, orange-brown as it ages, with UV rays (or the lack thereof) and humidity playing a key role in the way in which the luminous material transforms. However, many tritium dials seemingly don’t change at all…or are changing at remarkably slow rates. To answer your last question, there has always been variance in luminous paint batches. Although created at generally the same time, a handset can receive one mixture and the dial’s luminous hour plots can receive another like-but-subtly different mixture. The (different) chemical compounds react to the environment as they do, and that’s why an all original parts vintage timepiece can look “off” when in fact it’s 100% unmolested.
@onthedial when you refer to moisture intrusion that can be recognized across brands - is that always the mossy green/black color? and somewhat related... why are there watches with index markers where the lume is broken (like a stick broken in half, with one half still remaining), or simply missing lume plots? Is that something that can only happen during servicing, or does that happen due to age/environment and the lume simply detaches from the dial (not sure how it would "break" in half though)
Based on my limited observation, the best vintage Wittnauer's seem to have the most incredible, consistently beautiful lume when compared to other top-quality example from other brands. I've always wondered if that had to do with the specific makeup of the lume they used. Could also very well be me seeing something that isn't there.
@andomegas Recognizing signs of water damage (patterns) across brands, has less to do with color (though that can certainly be an indicator) than it does taking into account the manner in which the lume has been affected by the moisture. That is, I'd be much less inclined to think that a timepiece showing consistently even greenish-tint lume plots had been water damaged, than I would seeing one wherein the lume plots are jarringly inconsistent...some looking very faded while the rest look fine; some showing signs of separation/lift-off from the dial laquer/paint, some looking blotchy, etc.). Obviously, there are other signs too: rust/spotting around the rehaut, corrosion on the handset, flaking of the laquer, etc. [2nd part to your question] You have to remember that a vintage watch is going to be, at minimum, 25 years old. And if we're not talking dress watches, these timepieces were tool watches--they have seen a lotta life! It's through daily wear/use over many years that a lume plot can become dislodged, or even separate in half. It's an unfortunate but natural event. The damage should not occur during a service. However, a good watchmaker can glue/stabilize existing lume that might be swimming in and around the dial. Often times, though, it's too far gone and it's basically dust. IMHO I would say that luminous paint that's applied within a channel (on a handset, on the hours markers) tends to be more impervious to damage than "unframed" lume dots.
Thanks again for the help - lots new to me in there. Interesting about the ability to glue/stabilize existing lume. Affixing half a lume plot/strip in a way that it isn't noticeable must require quite a steady hand!