A Question about Tritium

[highoeyazmuhudee]

im trying to find a straight answer to the mystery of why some dials decay to orange and others can remain a creamy white.

its a known fact that tritium has a half life of 12.5 years, i have a gen dial that is older than this half life, i will say even a full life. the hour indices remain an almond.

now the question is, will this dials markers decay further causing the color to change or since the tritium is no longer active at all there will be no catalyst to cause the decay and they will remain an almond color indefinitely.

[sneed12]

Two things:

1) the half-life is the time it takes for the radioactive activity (defined as the number of decays/second) to reduce to half of its current value. The curve asymptotically approaches zero, but never gets there. The tritium in your watch is definitely still active, just ~1/4 as active as it used to be (after two half lives the activity is (1/2)^2)

2) I don't know if the only thing that causes tritium lume to yellow is the decay of the tritium itself. The stuff in the markers is not just tritium, but a paint base, phosphorescent material, etc. The yellowing is likely due to a complex set of factors, only one of which is the aging of the tritium itself. After all, regular old paint turns yellow without any radioactive decay at all.

<--physicist

[praetor]

what you're suggesting is that tritium causes patina when in fact it isn't that clear what causes it. The decay of the tritium should mostly cause the decrease in the amount of luminescence of the dial markers. I think dial patina has to do more with aging and exposure to the elements rather than tritium itself. The only correlation I've heard of with respect to patina (not verified) is that watches stored in safes tend to be darker in color whereas worn watches are lighter. It might have something to do with the sun bleaching the markers... who knows.

Also, in theory your tritium will never disappear. It's just a simple half life calculation: After 25 years, it should have 25% remaining, and 37.5 years 12.5% remaining and so on.

[lhooq]

The only correlation I've heard of with respect to patina (not verified) is that watches stored in safes tend to be darker in color whereas worn watches are lighter.

The causes of patination have been discussed on VRF a number of times, but I don't think it's been resolved one way or another. I do remember reading one thread in which someone posted a picture of his 50s-era Subs--all safe queens, but with original tritium that was lily-white. There are a lot of factors at play, but I don't think anyone has sat down and taken a scientific approach to figuring out which does what.

I was discussing a related question with an acquaintance recently: Why does the the average mid-60s Omega Seamaster 300 looks so much worse (in terms of wear) than the average mid-60s Submariner? Is it due to the numbers produced (more SM300s = more bad examples?) The activities of the average wearer? Or is it down to the design choices that Omega made i.e. push-in versus screw-down crown, plastic bezel inlaid with tritium versus metal insert?

[freddy333]

It is not the tritium that changes color, but the substrate (the material base into which the tritium is mixed). There have been many hypotheses as to what causes the discoloration, ranging from moisture to heat to lack of oxygen to UV, but until/unless Rolex provides the answer, you can take your pick.

[chefcook]

I tend to believe that UV helps to have a bright white on a Tritium watch. Usually the dark brown watches are those drawer finds that spent 20 years in the dark...

[sneed12]

There have been many hypotheses as to what causes the discoloration, ranging from moisture to heat to lack of oxygen to UV, but until/unless Rolex provides the answer

I doubt anyone at Rolex knows.

The vintage watch thing is something no one saw coming 40 years ago, so no one bothered to do controlled scientific experiments.

[Watchmeister]

It is not the tritium that changes color, but the substrate (the material base into which the tritium is mixed). There have been many hypotheses as to what causes the discoloration, ranging from moisture to heat to lack of oxygen to UV, but until/unless Rolex provides the answer, you can take your pick.

I am with Freddy. Tritium is a gas. Without some form of phosphorous material there is no glow. That material or substrate will have a huge impact on how your tritium ages in terms of luminosity, color and even amount of physical decay. Whether the tritium and its substrate is exposed to air, water or even sunlight will have a big impact as well. For all those reasons no two watches age the same - and IMHO that is what is cool about tritium. For my money Rolex is the one that found the best substrate for longevity. I have a '66 Rolex and it still glows and maintains a yellow rather than brown color better than my 10 year old Panerai's. In the past my watch smith has even made tritium with very different results based on the substrate.

[Rolexaddict]

sorry guys, I love you, but one again this is masturbation

[Watchmeister]

It is if you know the answer.

[highoeyazmuhudee]

i always assumed the radioactivity caused it to "burn" over time as ive observed with radium markers, some interesting answers here none the less.

[FxrAndy]

I have noted the same as stated above that the more light they get the whiter they stay.

[FxrAndy]

I have noted the same as stated above that the more light they get the whiter they stay.

[Watchmeister]

I have noted the same as stated above that the more light they get the whiter they stay.

If that is the case it is a function of the substrate (phosphorous adherent) and how it interacts with the tritium and any contaminants (air, light, water, etc.). Tritium is a gas.

[praetor]

tritium emits beta particle radiation or a charged electron only which might cause a chemical reaction given that the reactants are available because it gives it enough energy to do so. Radium emits alpha radiation, beta radiation and gamma rays which would in theory have more unknown effects.

Also, you can't really detect beta radiation from tritium with a Geiger counter, which is what you see in old panerais because it's not sensitive enough.

Edited June 8, 2011 by praetor

[Watchmeister]

Well that explains why I can get a reading from a geiger counter on a much older radium dial but not on a tritium one.

[freddy333]

My gen 1986 16014 (tritium)

http://s95.photobucket.com/albums/l127/freddydynip/?action=view&current=MVI_1736.mp4

My gen 1959 OPD (tritium)

http://s95.photobucket.com/albums/l127/freddydynip/?action=view&current=MVI_1735.mp4

[praetor]

^you might also want to note that plastic blocks beta radiation =P

[bruce79]

The topic has been beaten to death on VRF (as was mentioned above). There are several theories but no one really knows for sure. It's interesting though to look at Panerai. The patina on many of their models using tritium is quite remarkable. And these are watches that are 15 years old, not 40. It seems like it has more to do with the binding agent used with the tritium rather than the tritium itself. The quality of the binding agent and how that agent reacts with it's surrounding elements and how it holds up over time...would be my guess.

[Watchmeister]

One of these days I will have to chase down one of the VRF threads. It actually is a very simple topic. Tritium is a gas. How it ages or decays will be a function of its reaction to the substrate to which it is attached. Do folks who have t dial PAM's and vintage Rollies agree with me that Panerai's binding agent is (from a longeviy perpective) far inferior to Rolex's.In the case of Panerai I am also convinced that they put a top coating on some of their tritium dials. They certainly did it to some of their hand sets.

[Dizzy]

I tend to believe that UV helps to have a bright white on a Tritium watch. Usually the dark brown watches are those drawer finds that spent 20 years in the dark...

+1

There are many many threads regarding this on VRF and it seems that the safe-queens are the ones with the darkest patina, while the daily beaters (that are always exposed to sunlight and UV) have the lighter or white markers.

[highoeyazmuhudee]

i have a trit dial in a drawer for maybe a year now, looks the same to me.