, , ,

From about 1970, Seiko introduced an approach to many of their mid case designs that made use of Hardlex tempered mineral crystals bonded into a metal frame. The frame served a dual purpose of providing the sealing surface to a complex-profiled rubber gasket as well acting as a polished inner rehaut. This design of crystal was widely used in many Lord Matics, King Seikos, Grand Seikos, 7018 chronographs and some of the early quartz models.

This was also a time when Seiko became fond of using faceted crystals whose prominent profiles made them vulnerable to chips and scratches. Replacing such crystals at service was of course no problem when spare parts were in plentiful supply but here we are in 2018, nearly 50 years after this crystal design was first introduced, and supplies are fast running out – for some of the more commonly used part numbers, they are all but exhausted.

In the absence of an easily available replacement spare part, the obvious strategy must be to remove the battered old crystal from its frame and replace with a suitable alternative. This presents three problems, none of which trivially solved:

  • How do we remove the crystal from its frame cleanly without damaging the frame?
  • How do we identify and source a suitable replacement crystal to glue back into the frame?
  • How do we glue the new crystal into the frame in a way that is as invisible as possible?

Let’s tackle all three questions in the context of the two King Seiko watches whose stories so far are recounted in the two preceding posts.

1. Removing the crystal from its frame

The crystals were originally bonded into the metal frame very securely and the passage of time does not generally appear to have compromised that security. Consequently, you cannot simply press the crystal out from the rear hoping that the ancient glue will relinquish its grip. Heat seems like one obvious strategy but there is a danger that heat alone might tarnish the metal, warp the frame or crack the crystal, the latter adding to the potential to scratch the inner surface of the frame. In my early experiments with these crystals, I did try heat but I got nowhere – either I was too conservative in my approach or this strategy was doomed to fail from the start; a bit of a head-scratcher then. What else does a typical watchsmith have in their arsenal to throw at such a problem? How about the trusty ultrasonic bath? Let’s give that a try.

An extended blast immersed in water at room temperature was a somewhat disheartening experience, the crystal seemingly still disinclined to part company with its frame. Any good experimentalist will navigate their way to the solution to a problem by changing one variable at a time and so let’s stick to the ultrasonic bath but now elevate the temperature. A repeat performance at 50°C was no more successful than at 20°C and so I cranked up the heater on my ultrasonic bath to 80°C and ran it for a good 40 minutes as the temperature slowly crept up to about 75°C. Much to my relief, I seem to have hit upon the magic formula: my first guinea pig crystal, taken from the 5626-7000, separated easily once extracted from the bath.

The next step is to remove the glue residue from the metal frame but if you wait too long, the glue will harden again and its removal will be a protracted business that is much more likely to result in damage to the frame. The trick is to remove the glue while it is still warm and wet.

At this point then, we have a clean, undamaged metal frame and so we need now to identify a suitable glass crystal to glue back in.

2. Identifying a suitable replacement crystal

Both crystals from my two automatic King Seikos are 30 mm in diameter, but their frames are of different depths and profiles and incompatible with one another. The 5626-7000 takes the 300V04GNS crystal and the 5626-7111 uses the 300V16GNS. However, the glass in both appears to be of identical profile: essentially a flat top (possibly with a very subtle dome) with an inner dome and a clear polished bevel around the edge.

One option is simply to replace with a 30 mm flat crystal, and suitable candidates in this case could be something like one of the Sternkreuz facsimiles of the Seiko 300W19GN or 300W96GN crystals.

These are of different thicknesses and consequently the extent to which they will present themselves above the watch bezel will differ but either could provide a serviceable option. However, you will then lose the inner dome that, while fairly subtle in these watches, does have a noticeably pleasing optical effect.

To my mind, a better choice is to find a domed crystal. There aren’t too many generic options but one such is the Sternkreuz MD 300, a double-domed mineral glass crystal with a frosted bevel. Not a faithful replacement but to my eye, it represents a more charismatic choice over a bog standard flat crystal.

The third and arguably best option is to find a 30 mm V-type bonded crystal that is still in plentiful supply and which contains a glass of the same profile as that used in the 300V04 and 300V16 variants. The glass from the sacrificial crystal can then be removed using the technique described above and then re-bonded back into the correct frame. This is a very labour-intensive approach which requires you to set to one side the moral dilemma of vandalizing an otherwise perfectly serviceable crystal and for this reason I hesitate to recommend it, in spite of the fact that I have taken this approach for one of our two King Seikos.

3. Bonding the new crystal into the frame

This whole exercise will be utterly fruitless unless this final step can be achieved invisibly. I mean by this that it should not be possible, at least without the aid of a loupe, to discern any obvious signs that the crystal has been glued into the frame. The glue must therefore be of a type that dries clear and colourless, it must be applied evenly and there must be no signs of overspill. Of course it needs also to be water resistant and provide a secure and strong bond between glass and metal frame. I would avoid using any two-part epoxy glue – they tend not to dry invisibly and there is the danger that any unreacted hardener might leech through the joint and onto the dial.  I have tried two different types of glue, both designed specifically for glass and both requiring curing under UV light.

One of these can be purchased very cheaply, the other not! Having selected our adhesive, we need to apply it. Again, I’ve experimented with a number of approaches and the one I am happiest with is to use a sharpened tooth pick to apply a thin and even layer of the glue to the upper horizontal mating surface of the metal frame only.

Once you are satisfied that you’ve done this without contaminating the rehaut surface, press the clean crystal into the frame, working as required to even out the distribution of the glue. This is probably the most challenging part of the process to get right. Next, depending on whether you are using the superglue or the Seiko S-314, you can either cure the glue under direct sunlight or by using a UV curing lamp. The instructions for the Seiko glue suggest that you need to cure under UV light for up to an hour. The superglue supposedly requires just a few minutes in sunlight.

Assuming all has gone smoothly, you will at this point have a completely assembled crystal assembly that appears, to reasonably fussy external scrutiny, largely indistinguishable from a factory replacement part.  The photo below shows a new Seiko crystal harvested from another V-type frame, and bonded back into the original 300V16GNS frame from the KS 5626-7111.

Note the polished bevel at the edge of the glass. The second photo (below) shows a Sternkreuz MD300 crystal bonded into the original 300V04GNS frame from the KS 5626-7000. You should be able to see that this crystal stands a bit taller than the original and has a frosted bevel to the edge of the glass.

Both crystals look good when viewed from the top and so I undertake to go ahead and use these now to finish off the two King Seikos. We’ll see to what extent the choice of replacement crystal works in the third and final part of the automatic King Seiko trilogy (coming soon).