Lifting a digression from another post, but why do so many Omega Tritium dials not have a T.

Taken from the Moon watch only site

'The T indication only appeared in 1964 following a Swiss interior ministry ruling from October 1963 on radiation from luminous watch dials.

It required indication of the presence of radioactive substances and set forth a table of radiation limits, which came into force on January 1, 1964.'

Except that many 1970s watches with Tritium are not marked, while many others are. I used to see this as an annoying feature that made it harder to differentiate original dials from service replacements on certain models, but never really questioned the reason behind it.

So can anyone shed any light on this?

 

"Except that many 1970s watches with Tritium are not marked, while many others are. I used to see this as an annoying feature that made it harder to differentiate original dials from service replacements on certain models, but never really questioned the reason behind it."

Really? I've never seen any Omegas with original tritium dials that don't have Ts next to the "swiss made" inscription. Other brands of watches is another matter though.

 

Do you have any examples? Not uncommon with redialed watches, or ones where lume was added during a service.

 

Most Seamaster divers in the 1970s. SM200, SM600, SM1000, Big Blue, etc.

 

Although the TT regulation began in 1964, Speedmasters had shifted over to tritium lume, with no markings, a bit earlier. I think the change over occurred during 2998-6 production (1962-1963) as there are both radium lumed and no TT tritium lumed versions. All of the 105002-62 are tritium with no markings. The TTs began appearing with the 1964 production of later 105.012-63 and 105.003-63s.

I’ve seen tritium dialed 14755 Seamasters but I’m not sure if these were OEM or relumed by Omega. I believe there are both 165014-62 in 14755 radium dial and the 165014 tritium dial.

I have a 135.004-63 Railmaster with a tritium dial and a 135.004-63 PAF Railmaster/Seamaster wth a radium dial. Go figure.

 

That's interesting — is it possible that those divers were using something other than tritium?

 

They don't have tritium on them. Watch lumes are not exclusively made of tritium at all and don't even need tritium to glow.

 

Now this is interesting, what do the Seamaster divers from the 70’s use if it’s not tritium? I have all original 200M, 600 Ploprof, Big Blue and more coming, none has a T marking on their dials, so hence the interest. I myself believe they are using tritium in these watches.

 

Seiko wasn’t back then... my 68 still takes a charge and glows for a surprisingly long time.

 

No.

 

Not correct. Plenty of tritium lume dialled Omega watches have no T markings throughout the 70s, 80s and 90s. Not 321/861 Speedmasters though. Post ~1963 Those were always T marked if they had tritium on the dial. Zinc Sulphide is the phosphorescent component of the lume but it needs a radioactive source (or external UV stimulus) to excite it enough to glow hence the presence of tritium or on earlier times Radium. They stopped using Radium circa 1962 as it’s really not very nice.

Pic below is PreBond from circa 1990. Fitted with tritium dial at the factory. Not a sniff of a T. The Bond SMP that followed in the early 1990s is the same, no Ts. Same with the early Dynamic Gen 3 or the early Speedmaster Mk 40 which Hodinkee did the riff on recently. Omega transitioned to non radioactive Superluminova in 1996-7

If it was made by Omega between 1962/3 and mid 1996 and has lume on the dial, it left the factory with tritium stimulated lume material which will by now be pretty inert but should react strongly to UV. No idea why some models don’t say so but there it is.

 

Hmm and back to more research....thanks to @padders

While there does not seem to be any law in regards to marking dials it seems adheared to by many watch makers. Perhaps for military reasons? Hence why it appears on some but not others.

It appears the Seiko from the late 60’s which still glow with charging for 30 plus minutes might be due to higher concentrations of zinc sulfide which can glow for an hour when charges.

 

Seiko often do their own thing so I was very careful not to comment on what they use. For instance every one else uses doped Strontium Aluminate (branded as Superluminova) as lume today, Seiko use something else. It maybe similar but it is different enough for then to branded differently, from memory Lumibrite? Back in the day some manufacturers used Promethium based radioactive lume so there were alternatives, perhaps what you have is promethium? The isotope with the longest half life comes in at just under 18 years so is 50% more persistent than tritium. It would still be useful 36 years later.

 

More examples.

 

Seiko did use Promethium on their military issued chronographs and were marked with a P in a circle.

 

I wonder if the regulations changed around 1970 regarding the marking of dials. Omega carried on using T's on the dials already in production and stopped marking new dials?

 

What an amazing amount of knowledge and great conversations on this forum! This is the reason why I love visiting frequently as you will always, always learn something new. Thanks especially to @padders for sharing his vision and observations.

 

Well the dial went through 3 changes before 1978.

Rolex also marks as T<25 and others just T.

Again I think it was marked for military reasons after Swiss laws changed.

@padders mine and others Seiko from that period are known to take a charge but are not self illuminating like tritium or promeathium would be.

I’m not sure lumibrite as available pre 1980, or any other non self illuminated lume for that matter.

 

What dial are you referring to?

I have seen it said that T or T<25 refers to the strength but I am not sure about that.

I don't think it has anything to do with the military. They usually have that info more clearly highlighted and much less subtly, T Swiss T is present on numerous non military watches, just to indicate place of manufacture and the presence of Tritium to the watchmaker and general public.

 

You're so incorrect. Zinc sulphite absolutely doesn't need a radioactive source to glow. Light is sufficient for that (UV is light, if you happen to not know that).

Your last paragraph is quite meaningless with no source or reasons. Those lumes still glow under UV (ie. light) is proof enough that it doesn't have or need radioactive source to glow.