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The focal point of a watch is its dial — you don’t have to worry about the glass you have to pry. Furthermore, the pros and cons of different types of watch crystals are endlessly debated by enthusiasts. More than just a practical concern, good crystal also significantly affects design, user experience and usability in many ways.
You would be forgiven for being confused by some of the technical details found in the watch’s product descriptions regarding the crystals. Is sapphire better because it is more expensive than acrylic? What is a “box” crystal, anyway? And should you care about it? If you’re buying a watch, the answer to the latter question is definitely “yes.” The different materials, shapes and other aspects of watch crystals, however, require a bit more of a breakdown:
Learn the basics of watch crystal materials
The most common types of watch crystal materials are acrylic, mineral, and sapphire, and each has its advantages and tradeoffs. Preferences can vary, especially between sapphire and acrylic, although their physical properties are controversial.
Acrylic: Acrylic is a type of plastic, also known by Plexiglas, Hesalite, and other names, and is the crystal material you’ll find in vintage clocks. It scratches easily, but cracks rather than shatters, and this has led to some cases in which it is preferred over sapphire: the logic is that a watch can function with a cracked crystal, but the crystal is completely destroyed if it cracks. This is one of the reasons why you will find it used in some watches that are meant for hard use such as dive watches or especially the Omega Speedmaster Moonwatch (Hesalite version).
Some collectors also prefer the acrylic look for aesthetic reasons, citing its “glow” or “warmth” and the unique way it curves around the edges. Another advantage of acrylic is that it is inexpensive and can be shaped easily. While it scratches really easily, light scratches can be easily removed at home.
mineral: Mineral crystal is made from glass and hard minerals and is most common in affordable watches, especially from large Japanese companies. It chips without cracking, and while mineral is more scratch-resistant than acrylic, it does scratch and scratches aren’t easily buffed out. Seiko’s own version of the mineral crystal, Hardlex, has been hardened to improve scratch-resistance.
sapphire: A high choice for luxury and high-end watches, the sapphire used in watch crystals is a synthetic material (as opposed to a natural gemstone). One of the hardest materials on earth, it’s virtually impossible to scratch – an example of its scratch-resistance is the many flawless crystals found on watches whose cases have been beaten out of sight over the years. It also has impressive clarity, which makes dial elements look sharp and generally has a clean, high-end feel.
When not treated with an anti-reflective coating, however (more on that below), sapphire crystal is also highly reflective, detrimental to clarity. Also, while other materials can crack or chip, a sapphire can crack – although this has a very harsh effect and is an uncommon occurrence.
The primary drawback of sapphire crystal is that it tends to be more expensive. It requires high-tech production, and its hardness makes it difficult to work, especially in complex shapes. With better technology and increasing sourcing options, however, more entry-level brands have begun to offer it, and high-end brands have been able to do more, such as producing entire watch cases in sapphire.
These are the pros and cons of different watch crystal shapes
It’s not just the materials you need to consider: a crystal’s shape can make a big difference to both clarity and overall watch design and aesthetics. Domed and flat are the most common types you’ll find, but not all are created equal. Some models are more domed than others, and even flat crystals have a raised edge that makes them more visually interesting.
One of the most perfect examples of how crystal shape can affect your experience is in dive watches: a domed crystal leaves the dial completely underwater when viewed at an angle, while flat crystals are more clear. Flat crystals may provide better clarity in some cases, but they do not provide the depth and finesse of curved ones.
When evaluating a watch, you should look for its ability to easily read the time from any angle in any situation. For example, when a watch has a domed outer surface and a flat inner surface, extreme visual distortions can occur. That’s why watch brands proudly advertise “double-dome” crystals, meaning both the outer and inner surfaces are curved and provide a clear view of the dial, even from angles.
An interesting type of crystal is referred to as “box-shaped”. These are crystals that are prominently raised two millimeters above the bezel so that its edges are easily visible. This was common in vintage watches that used acrylic crystals, but modern technology has allowed more watchmakers to offer a shape built into the sapphire – negating the obvious problem that the protruding shape is an absolute scratch-magnet for acrylic crystals. Box crystal can add visual interest with its three-dimensional look as well as give modern watches a more vintage feel.
Look for reflections
As with every aspect of watches, you’ll find forum nerds debating the merits of so-called anti-reflective (or “AR”) coating. Also used for things like eyeglasses, telescopes and other lenses, AR coating is especially important in watches for glare-prone sapphire crystal. These coatings can reduce reflections as well as improve contrast, so what’s wrong with that?
Coatings on sapphire crystals are not very noticeable, but become more apparent when scratched. There are different types of AR coatings used by different companies, and some scratch more easily than others. To avoid unsightly scratches, some watchmakers only coat the underside of the crystal (which can reflect dial elements if left uncoated), but this results in a compromised and noticeably reflective crystal. Some enthusiasts sometimes complain about color appearing around the edges of the crystal or in reflections.
Regardless of its materials, shape, or other factors, a well-made and well-shaped crystal brings joy and elevates the watch. If all of the above sounds like something to consider when shopping, remember to at least evaluate the clarity of the crystal when shopping.
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