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Lessening fear of/ distaste for Acrylic.

3K views 24 replies 9 participants last post by  Scottish Steve 
#1 · (Edited)
I just cleaned an acrylic crystal, prior to sticking on a screen protector which I had to cut to fit. After realising I'd made a complete hash of the trim-job, I ditched the protector and decided to see how clean/unmarked my crystal was with a 15 times loupe. Holy Guacamole! This thing looks like the surface of the moon! Very unhappy indeed and wondering if I had been responsible, with my professional lenes-cleaning kit designed for DSLRs. But I persevered with a just-out-of-the-package microfibre lens cloth and got it more or less acceptable. I then remembered another acrylic crystal in need of TLC so I brought this one out and gave it 200 gentle swirls with the cloth. Holy Macaroni! This thing is polishing up nicely! Another 200 swirls (or about 3 mins) and it's perfect! Better than when I bloody well bought it! Back to the original watch. Now perfect also and no toothpaste involved.
I've been aware for some time now that acrylic is better at resisting shattering and maintains physical integrity in a shock as well as any crystal material, but have ALWAYS been suspect about them and wondered just why Sinn would put one in as an option on a 500 quid watch when they are so hard to keep immaculate. Now I know it's because they are so easy to return to that state. I don't know if I'm exactly an advocate, but tonight was very re-assuring and I won't be put off from a purchase by this material again. Anyone out there actively prefer acrylic? Speedmaster owners speak up!
 
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#2 ·
I am right there with you - I used to wonder why people liked acrylic, but after buying a vintage watch I grew to love it. Although it can scratch easily, it's easily polished (as you found out) and can give a watch a warm feel. I wish more manufacturers had acrylic as an option on their watches.
 
#4 ·
No big deal. My 30 year old Omega quartz has an acrylic crystal and it is easily polished or replaced if it gets badly scratched. Usually I had the service center polish it up when I got the battery replaced.
Most of my vintage stuff is also acrylic.
 
#5 ·
As vintage pieces predominate my collection I take acrylic - technically poly (methyl methacrylate) - for granted, and I have no wish to go sapphire at all. Point being: those who insist on sapphire tend to stick to one mantra: "sapphire is hard to scratch, acrylic can scratch" and that's it. But watches using acrylic crystals - which are almost invariably domed - actually use it structurally.

When the crystal is fitted into the front bezel with the help of a crystal lift, the curvature of the dome is slightly increased and the diameter minutely reduced. When installed, the crystal is trying to recover its original shape, so it is forcing itself against the bezel, effecting a tight interference fit. This also means the internal stress within the crystal is doing the work: the outside surface is under tension and the inside surface under compression.

As acrylic is a tough material it can withstand this internal stress with ease. However, if a domed sapphire - or mineral - crystal is installed in its place, the same internal stress makes it always near the verge of exploding, for it is a much more brittle material. In fact, exploding mineral crystals is not an unusual occurrence as it is easier to scratch than sapphire. Once the surface is scratched, the even loading of the stress on the front surface becomes disrupted, and the stress would escape by exploding.

Sure, sapphire is indeed harder to get scratched, but they can - and will get scratched nonetheless. For my money, I'd stick to acrylic without feeling it is "cheap", but be happy that it is the appropriate material for the purpose. In fact I even source modern compatible acrylic crystals to replace those on some of my watches, if they offer more desirable characteristics. For instance, I install modern slim crystals on my Vympel ultra-thins, which further reduce the overall thickness by 1mm... and that's an appealing thought indeed.
 
#7 ·
It seems you can never stop learning about this stuff, even the basics you thought you had boxed off years ago. The watch I originally worked on today was almost not bought due to the acrylic; now I've increased my knowledge and experience, increased my pleasure of ownership and potentially opened up a whole new world of vintage items to covet. Er, yeah, great idea! I can faintly hear my debit card whispering to me as I type!
 
#16 ·
Scottish Steve,

Short answer:
An appropriate acrylic crystal should be able to be polished repeatedly without reducing the thickness to the point that the integrity gets compromised, but I cannot possibly see how one can be so particular that the wear and tear over the space of one month becomes visible, to the point of being bothersome. I only polish the crystals on newly acquired vintage pieces which had been used for several decades.

Long answer:

Like I stated in my earlier post, when fitted to the watch, the outer surface of a domed crystal is under tension and the inner surface under compression. If an appropriate acrylic crystal is fitted, these stress loads would be well within what the toughness of the crystal can handle, therefore, if a minute amount of material has been removed from the front surface it can still stay good. You must have seen acrylic crystals which are gouged and deeply scratched, but still no catastrophic failure.

However, if an inappropriate crystal is fitted, then the stress loads would push it to the edge of structural integrity and perhaps beyond. By "inappropriate" it could be the quality of the material, crystal profile, and diameter.

Let's look at one example. You replace a domed acrylic crystal with one which is of lesser quality material, thinner, and slightly greater diameter. This means that the stress loads in the crystal itself is much greater. Supposing the loads are at a magnitude which exceeds the toughness of the material, soon after its installation - perhaps a few days - the front surface would start to break in a network of crazing, like craquelure on the surface of an old oil painting. an attempt to polish it - as in removing the surface material down to the level where there is no cracks - would speed up the destructive forces and you will make the crystal explode. At another forum there was a report on such a case.

A reputable watch manufacturer or repairer would never use crystals which are inappropriate; if the crystal is original to the watch then it should be just fine, and if a replacement is needed, an experienced repairer would get a proper replacement - perhaps of third-party manufacture - fitted which is totally within specs. I have used replacements by known firms like Stella, Robur, Sternkreuz etc and they are all very fine, including those by a defunct Australian firm Dean, which turned out to be superlative.
 
#18 ·
Thanks. I wasn't sure if acrylic, when polished, simply smoothed itself over or lost material, but it looks like I'd be totally unreasonable to worry about it in any way. This is good to know! As stated at the top, I was pleased to bring one just-out-the-box and one 4-5 month-old crystal up to never-been-worn std and in fact possibly a little better than factory q.c. allows. When I talk about a polish every month, I'm talking about a quick rub with a micro-cloth, not a full-on operation!
 
#20 ·
Here is an example of extreme acrylic crystal: the original one fitted to one of my Raketas I bought NOS (and I have several similar ones), the "big bubble" crystal...

Watch Watch accessory Strap Fashion accessory Metal


There's absolutely no need for Raketa to fit such an extreme high dome crystal, a much lower profile crystal would have easily cleared the hands, but they did it just for balancing the appearance when seen in profile. Of course I have no problem with it and since I got it more than a year ago I never had a need to polish it whatsoever, despite the height which would have made it more susceptible to scratches.
 
#22 ·
I give my watches a good clean about once every 6 weeks. I've only got 8 at the minute, so this is done quite quickly. And I'll almost always give whatever I'm
wearing that day a quick rub if it's a steel case. Twenty seconds tops. I'll need to just wait and see how things go with the acrylic. I'll probably be a little obsessive in the next few weeks/months then calm down.
 
#23 ·
I have two watches with acrylic crystals, and they scare the crap out of me every time I wear them. They both have light scratches on the crystal, but they're not noticeable to the naked eye unless you catch a reflection of a light source at the right angle. But still. I don't really shy away from it, though (though for my last purchase, I did specifically); I could easily have gotten my Speedy with the sapphire crystal, but went acrylic.
 
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