Mineral crystal, sapphire glass, sapphire-coated mineral glass, acrylic glass… The type of watch crystal impacts the watch’s durability, so it’s worth paying attention to. How do these crystals differ from one another? Let us explain.
Different Types of Watch Crystals
Wristwatch crystals are generally divided into three materials: acrylic, mineral, and sapphire. Additionally, a coating can be applied to improve the properties of each material.
Acrylic Crystal
Acrylic crystal is a plastic-based material sometimes used in watch crystals. As a softer material, it scratches easily. However, it can be polished a few times to remove scratches, and its flexibility helps it withstand impacts without shattering. Acrylic is an affordable material commonly found in children’s watches.
Mineral Crystal
Mineral crystal is made of glass, and it doesn’t scratch as easily as acrylic. Almost all mineral crystals today are tempered, meaning they are heat-strengthened to increase the surface hardness, making them more resistant to scratches and breakage.
Mineral crystal is relatively hard and durable but doesn’t give upon impact and can shatter. Scratches on mineral crystal cannot be polished out, so replacement is necessary. Nonetheless, it holds up well under regular use and requires a strong impact to break.
Sapphire-Coated Mineral Crystal
To enhance the durability of mineral crystal, a thin sapphire layer can be added. This sapphire coating greatly increases the scratch resistance and hardness of the crystal’s surface, making it exceptionally resistant to scratches.
Sapphire Crystal
Sapphire crystals are now made from synthetic sapphire. This synthetic sapphire isn’t actually glass at all; it’s a highly durable, transparent material created by crystallizing pure aluminum oxide at extremely high temperatures. Synthetic sapphire has the same hardness as natural sapphire.
When heated, synthetic sapphire forms a mass that is then cut into pieces using diamond-coated saws. These pieces are shaped and polished into watch crystals. The tools required to cut and polish such a hard material contribute to the high cost of sapphire crystals.
Sapphire (natural or synthetic) is one of the hardest materials, with a hardness of 9 on the Mohs scale, which is used to measure the relative hardness of different materials. (Diamond ranks 10, the highest.) Watch crystals made of synthetic sapphire are often marketed as scratch-resistant.
At Aarni, we use both sapphire-coated mineral crystals and sapphire crystals in our watches.
