# Identifying a Radium Dial



## EPS

I'm aware of the dangers of radium dials and the associated dust. That said, I had a momentary lapse of reason when I got my vintage alarm clock (not a watch, sorry if it's not exactly on-topic) in the mail today and opened it up to wipe off the inside of the crystal. In my defense, I didn't realize that it was luminescing until I happened to position it in the sunlight, I hadn't thought about radium dials in a while, and the case's seal is anything but airtight (hence why I'd consider pitching it if it has radium).

I'm going to take the thing to my college's physics department to see if one of them has a Geiger counter to point at it, but meanwhile I have embarked upon a thought experiment that you all may find interesting, and I am questioning whether the dial has radium. Here's why:

1. The dial doesn't glow unless it's held very close to a bright light. The glow isn't brilliant, but it's certainly visible.
2. The dial becomes very dim in less than 5 minutes and is completely dark after well less than an hour. While I didn't press my eyeballs right up to the glass, I strained but still saw no glow.
3. No dead-giveaways, like "sterile," non-oxidized areas around the numbers or brown spots on the crystal. (An insufficient but necessary condition for ruling out radium).

Basically, the dial behaves exactly like the non-radioactive glow-in-the-dark stuff that they put in vampire teeth for Halloween costumes. That said, I'm concerned because the clock looks to have been made before 1950 and it does glow in the dark.

My reasoning is that any radium in the dial when it was made is still there now (the half-life is something like 1400 years). Thus, if it was a radium dial in 1940 or whenever, it's still just as much a radium dial today, and if a radium dial doesn't glow in the dark of its own accord, then it's because the zinc-sulfide paint has deteriorated. My dial glows in the dark when a light is shined on it, a property of zinc-sulfide, so it probably contains some zinc-sulfide. The question is, _can the zinc-sulfide in a radium dial deteriorate to such a level that, while it still glows from being exposed to a very bright light, it does not spontaneously glow from the radium?_ If the answer is yes, then I may be in trouble; but if the answer is no, then I'm probably safe.

I've attached a picture of it, by the way; it's a Seth Thomas Echo 3E. I could be creating a false dichotomy here, and I won't know for sure until I've measured it. But do you guys have any thoughts? Does anyone else own one of these and know about its dial? Thanks for your help.


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## Janne

That isa very, very nice Art Deco design.

I would expect it had Radium in the Luminous numbers.
The answer to your question is YES.


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## StufflerMike

Mine does not glow any more either. Don't knwo what the lume compound is made of. If radium it would do no harm (ARPANSA - Radium Paint in Wrist Watches)


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## Bfisher

Buy a cheap dosimeter... there is plenty on the bay. That's the only way to be sure... btw my old clock had radium and it don't glows in the dark.


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## EPS

Janne, thanks, it looks even better since I wiped the crystal and rubbed some pledge on it, although now I'm wishing I'd stuck with just the pledge.

The problem is that it doesn't glow by itself, but it does glow if one holds it up to a light source. I just don't know if there could be enough zinc-sulfide to glow from exposure to light but not enough to glow from the radium alone. I agree that the only way to be sure will be a radiation detector, but I'm curious to see if this rough reckoning works. People always say that, if it's from pre 1950 and it glows in the dark _even without exposure to light_, it's almost surely radium. But is it correct to say that, if it's from pre 1950 and it _does not _glow in the dark _without exposure to light_ but _does_ glow _with exposure to light_, it probably has no radium?

Thanks for the replies, and I do like the clock Mike posted. I'd be curious to hear some more opinions, and I'll post what I find out from the Physics Department.


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## Janne

My 1944 Laco B-uhr has Radium lume. It behaves exactly the same way as your clock.
Just do not worry, it is virtually harmless.
If you do not want to keep your clock, sell it.


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## mrsnak

Shouldn't this be in the vintage forum? Radium hasn't been used in watches in decades.
I guess clocks are good.

Here's a good recent thread of radium:

https://www.watchuseek.com/f11/how-dangerous-501090.html


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## EPS

I just checked with one of the professors. The Geiger counter registered .3 millirems/hr at one inch from the dial. This is equivalent to .003 mSv (millisieverts) per hour. At a distance of 10 inches from the dial, the dosage would be 100 times less, equivalent to about .00003 mSv/hr. This is, as far as I can tell, equivalent to the natural background radiation of .00003 mSv/hr that we incur merely from background cosmic radiation. Thus, assuming that one spends 1/3 of one's time 10 inches away from the clock in bed, using one of these alarm clocks would cause one to incur an average of .00001 mSv/hr annually more than one otherwise would. This seems much less significant than deciding to move from the coastal plains to the Rocky Mountains (which would increase your annual exposure by at least .00004 mSv/hr), so I'm not particularly worried about the radiation from the dial. Now I just need to figure out if the dust or radon gas is a significant concern. Thanks for all of your help.


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## Mechmovt

Hi All,

This is a VERY late reply, but I was wondering if anything happened in regards to your health?

I have just worked on a radium watch without realising, and I have blown out some of the parts, and serviced the rest of the watch. As soon as I realised it was Radium, I put the parts in a box, and cleaned the case and dial with windex and toilet paper, wearing gloves. I thought it would be best to clean it with something wet as to avoid particles going everywhere else. I then used a UV light to find any flakes on my desk, and I cleaned them away too.

Cheers.


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## ScienceDude

.003 mSv/hr is 3 µSv/hr. At that dose rate, you get a whole year's worth of dental x-rays every single day. Take a look at this entertaining and informative lecture, geared to laypersons. It is by Dr Richard Muller, a Berkeley physics professor. Right away, he addresses radium watches. His opinion is not to keep it as an interesting artifact, but not to wear it. Additionally, it is important to realize that disturbing the paint in any way is very hazardous because you might accidentally ingest, inhale or embed the material in your body. Its a small danger, but it is definitely a danger. Physics 10 - Lecture 05: Radioactivity - YouTube


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## tatooist77

Great info, thank you experts


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