For some it might be surprising, but despite the name, sapphire crystal used in watchmaking has nothing to do with this precious gemstone. Synthetic sapphire which protects the dial is just a variety of corundum - a crystalline form of aluminium oxide. So why is this type of crystal so desired?

The answer is really simple! Sapphire has some characteristics which make it look luxurious and extravagant. But the most important thing is that it is considered as one of the hardest natural minerals. On the Mohs scale it has 9 points, which means it can be scratched only by a diamond. For instance, talc has only one point and it can be damaged even with a nail. Synthetic sapphire with such a high score on the scale ensures flawless appearance for a really long time.

Another advantage is its high clarity (85%). It means that this type of crystal is not only clear, but also as lucent as valuable objects can be. Due to those attributes, they are highly admired by pilots. Sapphire crystals are often covered with anti-reflective coating, which facilitates telling the time during the flight. It is hard to find a good-quality pilot watch without fine sapphire glass.

The process of sapphire production is really complex and it requires a lot of knowledge and experience. Perfect surface finishing is a key to success, but it can be highly problematic. It turns out that the biggest advantage of this type of crystal, exquisite hardness, can be a nuisance during the production process. In sapphire processing, the saws with diamond blades and diamond grindstones are used, as well as polishing powder made of diamond dust. That is why only dedicated factories make sapphire crystals. One of them is located in Switzerland, in the city of Le Locle. They produce crystals for brands like Tissot and Certina. Sapphire glass became a standard for many famous companies, mostly Swiss, like Doxa, Atlantic, Roamer, or Adriatica. This type of crystal can be found also in Japanese watches, like Orient or Seiko.

It is worth mentioning that sapphire crystals are the most durable type of watch glass, however, it doesn’t mean it can’t break. Their hardness is the reason why they are so fragile and not break-proof. Fortunately, glass damage does not happen too often - mostly during sports. That is why there are not many sports watches with sapphire crystal.