What is sapphire crystal?
Synthetic sapphire, a lab-grown crystal of aluminium oxide that's almost impossible to scratch, used to cover the dial of most good watches.
Sapphire, mineral and acrylic
Sapphire rates 9 on the Mohs hardness scale, second only to diamond, so keys, walls and desk edges won't scratch it. It's grown as a crystal, sliced and polished, which is why it costs more than glass. It can still chip or shatter from a hard, sharp impact.
Mineral crystal is hardened glass, around 5 to 6 on the Mohs scale: cheaper, more scratch-prone, and common on affordable watches. Seiko's proprietary hardened mineral glass is called Hardlex.
Acrylic, sometimes called hesalite or plexiglass, is plastic. It scratches easily, but the scratches polish out with a paste like Polywatch, and it flexes instead of shattering, which is why the Omega Speedmaster Moonwatch kept it for space. It also gives vintage-style watches a warm, domed look.
Anti-reflective coating
Sapphire is very reflective, so most watches add an anti-reflective coating on the inside of the crystal, the outside, or both. Coating on the outside works best but can scratch, leaving a smudge-like mark even though the sapphire beneath is fine.
Which crystal at which price
| Price | Sapphire | Mineral | Acrylic | Watches |
|---|---|---|---|---|
| Under $500 | 32% | 59% | 9% | 101 |
| $500 to $1,500 | 87% | 13% | 0% | 100 |
| $1,500 to $5,000 | 100% | 0% | 0% | 99 |
| $5,000 and up | 99% | 0% | 1% | 106 |
Current watches in our catalog, which is weighted to popular enthusiast models.
Questions
- Is sapphire crystal worth it?
- For a watch you wear every day, yes: it will look new for decades. Mineral and acrylic are fine on cheaper watches, and acrylic is easy to refresh.
- Can sapphire crystal scratch?
- Only from materials harder than it, mainly diamond and some ceramics or concrete grit. A visible mark is more often a scratched anti-reflective coating.