Summer activities, especially water sports, can be hard on the wristwatch — and its crystal. The crystal is the clear cover that goes over the dial and protects it. Depending on what that crystal is made of, it can get scratched or even broken if hit too hard. It is a good idea to know what sort of crystal your watch, or the watch you are thinking of buying, is equipped with.
There are typically three main types of crystals used in watches: sapphire crystal, mineral crystal and hesalite crystal. The one your watch features is often reflected in the retail price of the watch. Here, we take a look at each material individually.
Sapphire crystals are the preferred choice in luxury watches because they are extremely strong and scratch resistant. They are also the more expensive of the three crystal choices. While this crystal is called sapphire, it should be noted that it is not made from naturally mined sapphire. Instead, the crystals are created as a synthetic compound — and hold the same properties as its natural counterpart.
The process of producing sapphires synthetically was invented in 1893 by French chemist Auguste Victor Louis Verneuil, and shared with the world in 1902. It's formal name is the Verneuil Process, but is more commonly referred to as flame fusion. Essentially, a long column of synthetic sapphire is manufactured in a special furnace using powdered aluminum oxide particles. When they reach temperatures over 2000 degrees Celsius, they melt and then fuse with one another to re-crystallize in a new column form.
The column is then sliced (with diamond-tipped cutters) to a specific millimeter of thickness and polished to become a watch crystal. Sapphire crystals, as mentioned, are more able to resist scratching and breakage. Anti-reflective coatings can be added to both sides of the crystal without any hazing.
Mineral Glass Crystals:
Generally a mineral crystal is an ordinary glass crystal that has been heat treated or chemically treated to withstand scratches. However, it is not as scratch-resistant as sapphire and is, therefore, typically used in mid-priced watches where cost is a factor (as mineral glass is less expensive to use than sapphire crystal). Under extreme hot or cold conditions – if the glass is bluntly hit on a certain angle – the glass can crack or shatter. The main benefit to mineral glass crystal lies in its price.
Also referred to as plastic crystals, Plexiglas, or acrylic crystals, these are the least expensive option and are most commonly found on lower-priced wristwatches. Plastic will not shatter or crack, but it scratches very easily.