Double-sided sapphire crystal: why it's the best choice for a watch

When it comes to watch crystals, three materials dominate the market: mineral crystal, acrylic crystal, and sapphire crystal. At A★Star, we chose double-sided sapphire. Here is why this choice makes all the difference.

The three types of watch crystals

Acrylic crystal

The cheapest of the three. It scratches easily but can be polished to remove superficial scratches. It is mainly found on entry-level watches.

Mineral crystal

More resistant than acrylic, heat-treated to withstand everyday impacts. It is the standard for most mid-range watches. However, it scratches when in contact with hard materials.

Sapphire crystal

The ultimate choice. Synthetic sapphire has a hardness of 9 on the Mohs scale—only diamond is harder. In practical terms, it is virtually impossible to scratch under normal conditions of use. It is the material used by major Swiss watchmaking houses for their luxury watches.

What is double-sided treatment?

Double-sided anti-reflective treatment involves applying several layers of anti-reflective coating to both surfaces of the crystal—the inside and the outside. The result: light passes through the crystal without reflecting, offering perfect readability even in direct sunlight or under direct lighting.

Without this treatment, a sapphire crystal can paradoxically be harder to read than a mineral crystal because of its reflections. Double-sided treatment eliminates this problem.

Why A★Star chose double-sided sapphire

On a watch with a star dial, the transparency of the crystal is essential. A star dial deserves to be seen in all its depth, without unwanted reflections obscuring the sparkle of the particles. Double-sided sapphire crystal ensures that you see your dial exactly as it is—at all times, in all lighting conditions.

It is a premium component generally found on watches sold for two to three times the price of ours. At A★Star, it is the standard.