“Anti-radiation shield” under dial?

Hi all, wanted to share an interesting discovery/quirk of at least the 7150-1 and possibly others in the diver lineup.

Reviewing mitkawatch’s YouTube service of a 7150-1 (link below) the other night, I was surprised at 9:20 when he removed what appears to be a dense metal plate (steel, iron, lead?), perforated for the dial feet, from the backside of the dial. He identifies it as a spacer, which made sense to me at the time, but in reviewing a 1964 USA catalog description (thank you Peter’s Vintage Longines Watches) of what appears to be the same reference, mention is made of an “anti-radiation shield under dial”, which surely is referring to the same metal plate observed in the servicing video.

Curious if this has been discussed before on OF or elsewhere (couldn’t find anything with a quick search). Are we thinking this design choice is a regular spacer (cleverly marketed as a feature), a genuine measure to mitigate the understood concerns around radium lume, or incorporated to serve some other purpose - anti-magnetism, for example? Furthermore, is anyone aware of a similar “feature” on other watches, Longines or otherwise?

Thanks!



mitkawatch 7150-1 Cal. 290 service:
1964 Longines Catalog USA, from Peter’s Vintage Longines Watches: https://www.vintagelongines.com/index.html#brochure13

Thanks for the kind words @DirtyDozen12.

Looking at the dark grayish color of the metal disk vs. other "soft iron" inner cases/casebacks I've seen (all of which look more like a dull mild steel), I have to lean towards the lead hypothesis, which, as you mention, would block certain types of radiation (most relevantly, gamma). Could be a very interesting (and practical) artifact of Swiss watchmaking reacting to the public's evolving awareness of radium's dangers.

I've got a 7150-1 arriving in a couple weeks that is overdue for a service. I'll see if my watchmaker can write his name with the disk - and put this mystery to bed!

Juergen

Certainly plausible - It is worth noting that while a regular caseback/movement blocks the heaviest (and hazardous) radiation particles (alpha, beta), it is ineffective at stopping gamma radiation, which lead (at least theoretically, at the right thickness) would block. Note that there's minimal practical benefit to this, as gamma radiation passes right through you anyways without causing harm.

Courtesy of Andy at Ultra-Vintage watches, here’s a pic of my 7150-1 dial next to its original spacer.


Most interestingly, he has confirmed the disk is lead, which, when paired with the period “anti-radiation shield” marketing, to me implies some “anti-radiation” intentionality in its material selection, if not fitment altogether.

While not particularly functional as a “feature”, it’s definitely an interesting quirk of an iconic watch.

Juergen