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I just received two watches that are identical except that they seem to be made a year apart (1995 and 1996). Both SHC divers (the only real difference is the inside of the caseback on one is stamped Singapore, and the other is stamped Japan). The lume on one is still fairly and uniformly bright on the dial, hands, and bezel pip. The lume on the other is completey shot (as in, completely).

Which got me thinking....what causes lume to go bad over time? The gadget person in me wants to think that, like rechargeable batteries, they're only good for so many cycles of recharge/discharge. But I'm not really sure this is true. So, I thought I'd throw it out to the (more knowlegeable) masses!

(On a side note....is completely shot lume on a watch from 1995 any cause for worry?)
 

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I think you're on the right track that there's a finite number of times that they can recharge and discharge, and different types of lume will certainly have different life expectancies. However, with two identical watches, it's more of a mystery.

Having relumed a couple watches, I would attribute the difference to the mixture itself. If the lume/binder mix isn't consistent, the lume definitely has a different appearance and it ages differently. For example, when I've used too much binder, the lume mixture is a bit runny and doesn't really glow very strong. It's fairly reasonable to imagine that, despite efforts to maintain quality control, the lume just wasn't mixed the same way in both places.

As for concern re: a watch from '95 losing its lume, I wouldn't be alarmed. To be honest, I'm impressed that the '96 is still bright.
 

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I have two SHC divers sawtooths if that is what you are referring to both have the brightest lumes of any of my dive watches. 96 & 97 manufactured both are still around the same. I have a 90 quartz diver that was an everyday beater for 20+ years and still has a decent lume on it. I think Chevere's comment is pretty accurate with proper mixture and loss over time a lot of factors there.
 

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Which got me thinking....what causes lume to go bad over time? The gadget person in me wants to think that, like rechargeable batteries, they're only good for so many cycles of recharge/discharge. But I'm not really sure this is true. So, I thought I'd throw it out to the (more knowlegeable) masses!
Sadly nothing lasts forever......
 

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Discussion Starter #7
I have two SHC divers sawtooths if that is what you are referring to...
Actually, it's a pair of (from best I can tell) SHC033's. Case number on one is 7N36-7A08, the other is 7N36-7A09. I was wrong, the first was made in 97, the latter in 95. There are some subtle differences in the case (more distinct flat surfaces and edges in the 7A08 than in the 7A09 - and given their apparent neglect, I don't believe the edges in the latter were polished away!), and as I'd mentioned earlier, the 08 caseback is stamped Singapore, whereas the 09 is stamped Japan. Also, interestingly, the wave logo is different. It's raised on the newer/08, and indented on the older 09.

If one was made in Japan and the other in Singapore I could believe the suggestion that different factories quality control lead to different lume mixtures (this is assuming that the different country stamps indicate different factories, and not simply different parts suppliers). But, if that's the case, I would have guessed the Japan lume would have been better. Anyway, I know you all love pics, so here ya go!
 

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Krusty Olde Pharte
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I think that the lume material is key. In about 1996 or 97 Seiko changed from their earlier (promethium?) lume material to the Lumibrite that they now use. Virtually any watch with the older type lume will show little or no lume now, even when charged with a UV light. Virtually any watch with Lumibrite lume will show essentially undegraded lume as compared to a new watch, assuming the same type (dive watch to dive watch, etc.) of watch.
 

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twall3-

I think there could be a couple more possible reasons to consider for the lume degradation in your watches in addition to the discharge/recharge cycling fatigue spoken of thus far:

1. Water impregnation by sea water or fresh water moisture could create a variance in the lume performance in a watch. As in tritium weapon sites, they are often permanently sealed in resin which is impervious to weather, solvent etc. Is there any evidence of either watch having been opened for service or maintenance addressing this possibility ?

2. The two watches could have lived their lives in vastly different lighting environments. For instance, one could have spent much of its life in a sock drawer whereas the other watch's lume could have cycled, (discharge/recharge) much more often based on the rigors of what was required of it.
I am sure you will excellent suggestions from the knowledgeable folks here at SCWF.
 

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Discussion Starter #10
twall3-

I think there could be a couple more possible reasons to consider for the lume degradation in your watches in addition to the discharge/recharge cycling fatigue spoken of thus far:

1. Water impregnation by sea water or fresh water moisture could create a variance in the lume performance in a watch. As in tritium weapon sites, they are often permanently sealed in resin which is impervious to weather, solvent etc. Is there any evidence of either watch having been opened for service or maintenance addressing this possibility ?

2. The two watches could have lived their lives in vastly different lighting environments. For instance, one could have spent much of its life in a sock drawer whereas the other watch's lume could have cycled, (discharge/recharge) much more often based on the rigors of what was required of it.
I am sure you will excellent suggestions from the knowledgeable folks here at SCWF.
These are both interesting points. The newer watch (7A08) was missing the caseback gasket, and also the second hand was bent very slightly up towards the crystal...certainly not something you'd get with a simple battery change!. The 7A09 seems largely untouched. Yet, the 7A08's lume is just fine. The seller of the older 7A09 said it had been a daily wearer and that he dove with it a lot (the watch came from Florida), so the notion of more recharge/discharge cycles seems more plausible there.

However, given the production dates (and also now that I have a decent google search term in "promethium"), I think that the notion of different lume material between the two watches is the more likely explanation. Looking at the markers with a loupe, the older watch's lume has a sort of dusty and slightly rougher texture, whereas the 7A08 is notably smoother with a slight shine to it.
 
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