[time-nuts] Atomic Clocks: It is important that they keep good time, Part 1

[Bob Bownes]

Interesting. I was wondering this as well now that time-nuts has gotten me
into collecting vintage (pre WWII) chronographs. Some are radium, some not,
most are in need of a good repaint either way.

But I do know that tritium gun sights are also a thing. Are those all
mil-surplus or using some secret source of tritium paint...

BTW, latest acquisition in the Vintage watch collection is a 1916 Waltham,
made nearby, with still a local watch shop specializing in them. Looking
forward to it's arrival.


On Mon, Jan 7, 2019 at 1:48 PM Warren Kumari <warren at kumari.net> wrote:

> On Fri, Jan 4, 2019 at 6:59 PM Steve Allen <sla at ucolick.org> wrote:
>
> > On Fri 2019-01-04T17:05:21-0500 paul swed hath writ:
> > > Ed agree with your coment that a 30 or greater year old led may be
> > dimming.
> >
> > Not nearly as much as an entirely different clock illumination:
> > radium watch dial paint
>
> I remember my mom's wind-up travel clock glowing brightly.  50 years
> > later there is nothing.
>
>
>
> I used to have a Rolex submariner with a tritium paint based dial -- I
> really loved the watch, but the tritium had sufficiently decayed that it
> would no longer fluoresce - this didn't affect the utility, but made me
> sad.... It was made in ~1989 and marked SWISS T < 25 for "less than 25
> milliCurie" (apparently much less, they started out at ~5 milliCurie). In
> ~2016, the tritium would have decayed to ~1 milliCurie. Tritium paint is
> (apparently) no longer legal in the USA, but when I was in Hong Kong I
> found someone who had "new" paint, and willing to repaint the face --
> unfortunately I didn't have time on that trip to have it done, and when I
> went back a few months later the shop had closed down...
>
> There is a (apparently) a group of watch dial enthusiasts who get a
> specific brand of tritium based exit sign which has tritium paint embedded
> in the plastic (most tritium exit signs are the small gas capsules
> instead), grind them up and then extract the paint from the ground plastic
> using solvents. I briefly toyed with this idea before deciding this was bad
> mojo and sold the watch...
>
>
> > I brought it into the lab just to check that
> > it is still radioactive (wouldn't want to have lost that radium
> > somewhere).  It's the zinc sulfide crystals, the radiation damages
> > them and they stop producing light.
> >
>
> Hmmmm. I wonder if that is actually what happens with the tritium paint -
> the dial I had would *just* have a visible glow if I had it in a perfectly
> dark room and let my eyes adjust for a while. If the tritium level had
> decayed from 5 milliCurie to 1 milliCurie I would have guessed that the
> glow should just have been 1/5th of original. The dial would still
> fluoresce nicely under UV, so I'm not sure what that means...
>
> W
>
>
> > --
> > Steve Allen                    <sla at ucolick.org>              WGS-84
> (GPS)
> > UCO/Lick Observatory--ISB 260  Natural Sciences II, Room 165  Lat
> > +36.99855
> > 1156 High Street               Voice: +1 831 459 3046         Lng
> > -122.06015
> > Santa Cruz, CA 95064           http://www.ucolick.org/~sla/   Hgt +250 m
> >
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>
>
> --
> I don't think the execution is relevant when it was obviously a bad idea in
> the first place.
> This is like putting rabid weasels in your pants, and later expressing
> regret at having chosen those particular rabid weasels and that pair of
> pants.
>    ---maf
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