We call the “watch glass,” the transparent cover on the top of your watch such as pendulum that protects the structures of the dial and ensures the visibility necessary for you to follow the essential functions of the watch. The choice of material is determined by the manufacturer and influences the use and quality of your watch. The most commonly used materials are acrylic, mineral crystal, and sapphire.
Acrylic “glass” watches are not glass but plastic. They are cheap; they lower the cost of production and have low protection against scratches; they can be polished, but not indefinitely. They are light, transparent, and resistant to drops, but they can scratch more easily. For this reason, “acrylic glass” is commonly used in children’s watches, lessening the worry of this “glass” breaking if they fall or bump into something while playing. Here are some examples of the use of acrylic in watches:
The most common material for the glasses of watches from brands such as Rolex is mineral crystal, perhaps because they make the piece’s value more accessible than sapphire glass. Mineral crystal has a hardness of 7 on the Mohs scale, which is considered a good hardness since few materials in the world have a hardness greater than 7. with a lot of friction, but it has good resistance for the day-to-day. In case of many scratches, the glass can be replaced by a specialized professional.
Fine watchmaking pieces typically work with a noble mineral called corundum, more commonly known as a sapphire. The watch glasses are synthetic sapphire made in the laboratory to have the clarity necessary for use in watches. Sapphire has a hardness of 9 on the Mohs scale, whereas diamond, the hardest material in the world, is grade 10 on this scale; that is, a diamond can only scratch sapphire. That’s why sapphire crystal watches elevate the watch category.
We must consider that hardness is a property that measures materials for scratch resistance. However, they can still be broken on impact. If you need to change your watch’s glass, it is essential to change it to another one of the same thicknesses because if it is thicker, it can be higher than the watch’s bezel, which can imply a probability of suffering a new impact and breaking again. It is essential to point out that the glass exchange must be done by a qualified professional to preserve the seal of your watch,