This week, Ahmed Zewail, the Egyptian-American Nobel prize-winning chemist died. Zewail pioneered the field of femtochemistry, a sub-discipline within chemistry in which ultrafast lasers are used to study the atomic scale dynamics of the chemical bond. The lasers he used produced a stream of very short pulses of light, each of which lasting a few tens of femtoseconds,* and much like a stroboscope appears to produce stop flow animation on the dance floor, so his lasers were able to take a series of snap shots of chemistry on the fly. One key aspect of this work was to provide experimental validation for the concept of the transition state, a term used to describe the loose aggregation of atoms arranged in a structure where chemical bonds are in the process of forming and breaking as colliding chemical reactants arrange themselves into chemical products. At the transition state, the system finds itself at a mathematical turning point, a maximum in the potential energy profile that describes the path from reactants to products. At this point the system can roll over the hill and the reaction proceeds to fruition or its can roll back from whence it came, resulting once again in a set of unreacted chemical components.

I like to think of Seiko’s activities through the 1960’s and 1970’s in terms of just such a potential energy profile, with, arguably, 1969 representing the transition state point. Seiko enthusiasts with an appreciation of the historical achievements of Seiko as a producer of wristwatches, will probably share my view that the period from 1960 to about 1980 was truly a golden era for the company but the peak of that period of creativity fell more or less at the half way point. It is difficult to regard the dynamic through the 1970’s as anything other than a decline as the quartz movement took hold and traditional watchmaking skills increasingly came to be regarded as old hat. This is not to say that there were not genuine highlights peppered through that later period – the classic 6309 and Tuna dive watches being obvious examples – but you only need to leaf though a Seiko catalogue from the mid 1970’s onward to realise where Seiko were placing their priorities at the time.

So why might 1969 be considered simultaneously as some sort of apotheosis yet also the start of a period of decline? Well, up to that point, we had seen the emergence of the King Seiko and Grand Seiko high-end sub-brands, comprising a range of watches spanning exquisite manual wind chronometers to high beat automatics. We had the beautiful one-button 57 series chronographs; the 62 and 61 series World Timers, the development of the classic Seiko divers watch, conceived in the Silverwave with the baton passing to the 62MAS and subsequently the 6105 150m divers. The Seiko Bell-Matic was another significant technical achievement of the decade. 1969 also notably marked the release of one of the world’s first automatic chronograph movements in the 6139A. If these are the highlights, we must not overlook the host of other beautiful and distinctive watches produced through the 1960’s that defined Seiko’s identity at the time.

After 1969 though, it is tempting to think that the lion’s share of their efforts went into the development of the quartz movement. Yes, we still had the cushion-cased 6105 and 6309’s to come, and the dual register 6138, developed from the 6139 but my sense is that the wind was shifting, the sails drooping and the highlights that followed in the subsequent 10 years all the more memorable for the rather niche roles they occupied in the vast ocean of the rather more forgettable mainstream output of the time.

In the midst of this then, we come to the sports diver, a water proof watch designed to be used in, around and under the water, but with a depth rating of 70m, not a pukka ISO-rated diver’s watch. These watches were marketed for their strong value as much as their prowess as divers watches: ‘Buy a Seiko underwater watch without going overboard” announces a US newspaper advert.

In another, the advert proclaims “Seiko on the summer surfing scene” with the blurb suggesting that “Wherever boys and girls are hanging five, you’ll find a ready-made market for Seiko precision waterproof watches”.

The first Seiko sports diver was probably the 6106-8100, produced between 1968 and 1969 in four dial variations, the most common of which is the dial shown in the advert pictured above. A few years ago, I somehow found myself having acquired two of these attractive watches, enamoured I suspect by their close similarity to the charismatic 6117-8000 World Timer featured here.

Superficially these two look identical. Both were produced in 1969; the one on the left in the March of that year and the one on the right in September. Those of you eagle of eye may have noticed that the earlier watch is marked as Water 70m Proof, whilst the later as Water 70M Resist.

The production of these two watches occurred during a period in which the standard nomenclature for indicating extent of resistance to water intrusion changed, driven largely by legislation in the USA. The change in the law came about in 1968 and watch manufacturers then started the gradual process of changing the markings on their watches from ‘Proof’ to ‘Resist’ or ‘Resistance’. In Seiko’s case, this process lasted until about 1971, after which all watches were marked as Water Resist, where appropriate. The fact that the earlier of our two sports divers is marked ‘Proof’ and the later ‘Resist’ is actually a red herring. The real reason for the different markings is that the earlier watch is a 6106-8100, intended for sale in markets outside the USA and which therefore did not have to adhere to the new standards quite so smartly, whilst the later watch is a 6106-8109, intended for the US market.

It is commonly the case that if I find myself with two of the same model both needing attention but only one of which gets the nod, then the other can end up languishing, neglected for an indeterminate amount of time before I stir up sufficient enthusiasm to attend to its needs (a good example of this is that the second of my two 6117-8000 World Timers still sits in my to do box, more than two years after I finished the first). So I thought what I’d do on this occasion is to service both watches simultaneously, report on the process and highlight key differences in the two as we go along.

First impressions of the two are driven by two factors: one is the general state of cleanliness of the later watch compared to the filth-encrusted first.

The second is the rather extravagant domed acrylic crystal fitted to the resist watch, patently non-standard but lending the watch a very appealing look.

With both watches opened, another key difference between the two becomes clear. The earlier watch is fitted with the B variant of the hacking 6106 movement and features chamfered bridges throughout. The later watch is the C variant, fitted with a straight edged train wheel bridge that contrasts with the chamfering elsewhere. This suggests to me that this bridge may have been substituted at some point in the past during a service.

So what distinguishes the B variant of the 6106 from the C variant? A clue can be gleaned from a view of the calendar side of each movement:

The B variant features a single language day wheel; the C variant, a dual language day wheel (in this case English and Spanish, most appropriate for a US market watch). Delving further beneath the surface and we note the presence of a day quick set lever on the C variant that is absent from the B variant. We have discussed the operation of the identical quickset mechanism on the 6119 before and so we can move on, noting only that both of these movements are 17 jewel movements and therefore refreshingly free from those pesky Diafix settings!

Servicing the 6106B proved straightforward, aided I think by the fact that it appeared not to have been serviced before and was therefore not saddled with the sorts of problems commonly deriving from the efforts of less than diligent watchmakers. Its inners though were very nearly as dirty as its outers. Here’s a close look at the pallet fork:

Moss? Seaweed? Spinach? Whatever it is, it stands no chance in the company of ammoniated watchmakers cleaning solution. I cleaned the two movements, one immediately after the other before then assembling the two in parallel. The two mainsprings looked more or less in similar good health and so both found their way back into service post clean.

Here’s a shot of the 6106B, part reassembled, awaiting its balance. Note the very nice decoration on the train wheel bridge.

The 6106C, noticeably cleaner all round having clearly been serviced in the past. However, it was this superficially nicer looking movement that threw up the only spanner into proceedings. The jewel bearing servicing the escape wheel on the train wheel bridge was chipped and needed replacing.

Luckily, I have plenty of 61-series spares and I managed to locate a replacement jewel.

With my jewel press pressed into service, the offending part was replaced and we were back in business.

The rest of the movement work was pretty much routine from here, with both showing more or less identical figures on the Timegrapher once the balances had been fitted and mainsprings wound.

As we slide well beyond the transition state in proceedings, we are now free to turn attention to the cases, the first order of business following a thorough clean to both, being selection of suitable crystals. I have numerous Seiko acrylic crystals nominally of the correct diameter and plenty of generic tension-ring equipped domed acrylics to choose from but this case variant turns out to be particularly fussy about its chosen partner. In particular, the profile of the tension ring turns out to be crucially important because the watch dial needs so sit within the volume of the crystal itself rather than flush with the bottom of the tension ring. Consequently, any crystal equipped with tension rings whose inner diameter profile does not provide sufficient clearance will not allow the movement then to sit correctly in the case. I experimented with a few permutations from my crystal selection but in the end the only crystals that fitted and were compatible with the dial requirements were those whose part number matched that suggested by my Casing Parts Guide from the period – i.e. 310T14AN.

The three you see in profile above all emerged from packets purporting to contain 310T14AN crystals. The one in the middle is a 310T14ANG with a gold tension ring and looks like it has the correct external soft dome suggested by the marketing photo in the advert towards the top of the post. Those at either end have sharper edge chamfers and are of different heights – both from packets labelled 310T14ANS. The one on the left would not seat at all in the case and so I was left with the central dome and the shorter, sharper crystal to the right, both of which seated with a satisfying click and both of whose tension rings allowed the movement and dial to locate properly in the case. I was a bit sad to have to replace the extravagant top hat crystal that came with my resist watch but it had been polished in the past and was too wavy and distorted to pass muster. We’ll see in a moment how these two look in situ but first I want to grapple with the turning rings.

As with the 62MAS and first gen 6105, the turning rings on these sports divers are freely rotating without click and are fixed using a bezel spring – a profiled piece of wire – whose inner edge sits in a channel on the case and whose outer edge sits in the reciprocal channel in the turning ring. In the photo below, we also see that there is a nylon gasket that sits in a channel below the turning ring in the case to act as a smooth surface against which the turning ring rotates.

Fitting can sometimes be a bit of an ordeal but I’ve had the greatest success by first fitting the spring to the case and then locating the turning ring first at the central apex of the spring following which I push the spring into the gap between the turning ring and case on each side until somehow it locates.

With the two turning rings fitted we can check out the very different looks of the two with their differently profiled crystals.

I do believe we are pretty much finished.   I’ll spare you the dial/hand fitting routine and jump straight to the finished articles.

The dials of both watches are truly excellent, very nearly mint although the Resist watch is marred a little by a slightly wonky SEIKO logo, probably clattered by the same watchmaker who chipped the jeweled bearing.

With that lovely soft acrylic dome, it looks great on the wrist.

The earlier Proof watch looks quite different with its flat box crystal.

The dial looks ever so slightly browner to me, compared to the grey starburst of the later watch. On the wrist the view of the dial is unimpeded by the reflections you get with the domed acrylic but I think it lacks the warmth, and perhaps a little of the personality of the other watch as a result. I may well end up replacing the crystal again but for the moment it’ll stay as is.

It’s been fun doing two at once, and interesting to note differences on the way that I might not have appreciated if I’d worked on these two separately. And with that, let’s wrap this one up.

* One femtosecond is 10^-15 second or one thousand billionth of a second. Those of you who like to think in decimals rather than exponentials might prefer to write it as 0.000000000000001 second. It might help to think of this in another way: a standard low beat mechanical watch movement might run at 18000 beats per hour. My high beat Grand Seiko runs at twice this rate at 36000 beats per hour. This latter figure is equivalent to 10 beats per second which we might alternatively express as 5 full oscillations (complete back and forth swings of the balance wheel) per second which can be expressed in terms of frequency as 5 Hertz. The apparently furious rate at which high beat watches tick can appear somewhat alarming – you fear for its safety – but 5 Hertz is a pifflingly sedentary rate compared to the rate at which molecular bonds vibrate. A water molecule undergoing a gentle vibration in its bending mode, in which the bond angle between central oxygen and the two hydrogen varies with time, is doing so at a frequency of just under 5 x 10¹³ Hertz – 50 thousand billion vibrations per second. This is why you need laser pulses in the femtosecond range to capture molecular motion.

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