If you think about it, there are effectively four types of watch crystals; sapphire, mineral, acrylic/polycarbonate and, to a lesser extent, various versions of Corning’s Gorilla Glass. There are also coatings for both scratch resistance and light refraction, but that’s a different topic.
Focus on the current dogma that dictates sapphire is king and THE preferred material for
better watches. After all, it’s almost scratch proof, so how can anything else compare?
While I do appreciate the nearly scratch-proof nature of sapphire crystals, I’ve also experienced their weaknesses, and I’m willing to bet I’m not the only one. Whether my catastrophic shattered crystal at the airport X-ray, or the time I smashed it into a door handle at home – sapphire might not take scratches, but it will and does fail completely when subjected to impact. It looked like new - until suddenly it didn’t.
Next stop, a somewhat costly repair that may necessitate a full disassembly to remove any shards that may have found their way into the nether regions of your watch. How it shattered is irrelevant, but at that moment of destruction, I’m certain most owners would have wished for a tougher option that would have withstood the particular impact.
In my experience, sapphire is best utilized as a flat crystal with its poor optical qualities mitigated by the use of (internal only) anti-reflective coatings. While domed versions are also popular, they do add additional risk for lateral impact but the light reflection may not be as attenuated.
One sapphire shape that I will rail against right here is the “boxed” crystals. These rise vertically from the bezel with a small step, and while they revisit a popular shape from vintage watches, the originals were almost always crafted from acrylic (hesalite) and were much tougher on impacts than the newer favorite sapphire.
Acrylic crystals do scratch easier, but they are optically superior, mechanically tougher, and relatively easy to buff out – or in the worst-case scenario, inexpensive to replace. If you do find a way to crack an acrylic crystal, they simply don’t shatter the same way a sapphire will, and repairs tend to be limited to the cost of the xtal and the basic installation.
In my opinion, mineral crystals are the worst of both worlds. While they are more scratch resistant than Hesalite, they are not nearly as tough. They are harder to break than sapphire, but will take scratches. In my experience mineral crystals in watchmaking should be reserved for exhibition backs only, where the likelihood of scratch or impact are nominal, and reflection of light less important.
Based on what I’ve learned, I’m almost certain that the Gorilla Glass (DX+ or Victus) is the very best material that ticks all the boxes. The only problem is that Corning does not make it easy for any watch brand to get the good stuff. Some smaller brands have used older versions of the glass, but the top-of-the-line materials are difficult to acquire (unless you are Apple, Android, or Nokia) and – if it matters, they are also fabricated in China.
I know a lot of experts out there may not agree with me, but after three decades of experience, contact with collectors and constant interactions with certified and master watchmakers, my opinion has evolved from a “Sapphire is King”, to a more rounded appreciation of what these materials are, and are not.
It’s AboutTime – To look through the right glass.
Gary George Girdvainis