Watch GlossarySapphire Crystal

What Is Sapphire Crystal On A Watch?

Sapphire crystal is a type of watch glass, a transparent cover fitted over the dial and very commonly as the window for a display caseback. It appears as the most inconsequential element of watchmaking, yet its placement is of utmost importance. The crystal cover acts like a protective layer to the dial and caseback. It also offers unobstructed views of the timekeeping elements on the dial, and of the partial or fully exposed watch movement on the caseback.

Qualities Of Sapphire Crystal

The sapphire crystal used in watches is of the synthetic kind, produced in laboratories by heating aluminium oxide to the point of crystallisation, then sliced into a round disc with diamond-coated saws and polished. This crystal ranks ninth on the Mohs scale (rating for mineral hardness) in steps of 1 to 10, equivalent to natural sapphire stones, qualifying amongst the hardest substances on Earth, making it highly scratch resistant.

The robust sapphire crystal, fitted over the dial of the Raymond Weil Maestro Ladies Diamond Automatic Moon Phase, showcases the Arabic numerals, brand logo, date aperture at three o’clock, and moon phase sub-dial at six o’clock with beautiful imagery of the moon against a starry night sky

The anti-reflective coating applied on the inside surface provides good legibility even under bright lights. Sapphire crystals are difficult to cut and polish, and require expensive horological tools to achieve good results. This makes the crystal costlier than other watch glass options such as mineral glass and Plexiglas (acrylic) options.