What does “Crystal” mean?

The crystal is the clear cover that protects the dial. Most modern luxury watches use sapphire crystal, a synthetic material that is highly scratch-resistant. Older watches typically used acrylic, a plastic that scratches more easily but can be polished; Hesalite is Omega's name for the acrylic used on the Speedmaster Professional. Mineral glass sits in between and is common on more affordable watches.

The crystal type helps date and identify a watch: Rolex moved its models to sapphire from around the late 1970s, while the Speedmaster Professional is still offered with Hesalite as well as sapphire. On vintage pieces, an original acrylic crystal with the correct markings can matter to collectors, although a later replacement is a normal service item. Check sapphire crystals for chips at the edge and acrylic ones for cracks or deep scratches. Anti-reflective coating on sapphire can wear, showing up as patchy reflections.

Example: 'Sapphire crystal, no chips, cyclops intact.'