Hey,

I'm trying to "date" some hands. Would you expect Tritium hands from the 60s to still faintly glow after 50 years? Or would that point to Radium hands?

Cheers

 

I know my Seamaster from about 1968 does not glow at all, and I doubt (don't know) if radium would either. Just my few pennies worth.

 

I know tritium won't be glowing. Radium should not either as it is not the radium that glows. It is the reaction with another material I can't remember just now, but has half life that's pretty short. Under a Geiger however a real radium dial should still chatter like Dennis's squirrel.

 

Are you sure they aren't just glowing slightly from reaction to light? Many times the Zinc Sulfide will react to light long after the Lume is dead.

 

Interesting - That was new to me!

Here is an excerpt from Wikipedia: "Radium paint used zinc sulfide phosphor, usually trace metal doped with copper (for green light), silver (blue-green), and more rarely copper-magnesium (for yellow-orange light). The phosphor degrades relatively fast and the dials lose luminosity in several years to a few decades, despite the long half-life of the Ra-226 isotope (1600 years)" https://en.wikipedia.org/wiki/Luminous_paint#Radium

 

The tritium is no longer active so the lume will not glow by itself, but some phosphor materials may not have completely degraded yet and still be reactive somewhat to light stimulation and then can glow a bit, usually for a few seconds or so.

 

You can have several identical watches from the same period, but the Lume will almost always respond differently, some will glow a lot under light, some won't glow at all. I believe it has to do with the concentration of Zinc Sulfide or other similar agent used in the Lume paste, and also with the way the Lume was coated... I.e. There are certain watches in which the Lume in the hands is lacquer based or coated in lacquer. This seems to preserve the photoluminescence to a point and they glow strongly under bright light, or at least glow visibly in ambient light.

In any event I don't think it's possible to date hands based on glow.... There are some very talented relume artists out there who make Lume paste which mimics old tritium perfectly.

 

Well... not exactly.

Half-life of tritium is about 25 years. So, 50 years later, you would expect about 1/4 the original lume from the radioactivity... but the paint oxydizes as well, so perhaps less from that.

I have had radium clocks that were kept such that the dial and hands were quite visible, at least to me, and in total darkness. But, the variability of the pain means that you can't go by radiation alone to determine whether it "should be glowing".

Tom

 

Tritium's half life is just a bit less than 12.5 years so after 50 years, it's only 1/16 or 6.25% left which is close to nothing usable for luminous excitement.

Radium, on the other hand, has half life of 1600 years, so if the phosphor is still good, it'd still glow. But there are different kind of materials to make phosphor, all of which degrade on many factors and after 50-60 years on a watch, not much would still glow. On a clock, it may do a bit better due to the better environment indoor that a clock would normally spend its life in.

 

Thanks for the correction, I misremembered!

Tom