Sapphire is the current best material for watch crystals. It's the mineral corundum, or alpha-Al2O3. Measuring a 9 out of 10 on the Mohs scale, sapphire is almost impossible to scratch, making it ideal for the face of a watch.
(Image credit: Wikimedia commons)
As explained nicely on Wikipedia, boules of crystal are slowly formed and sliced by wires and a diamond slurry, much like silicon for semiconductors.
- The very silly Tag Heuer phone has a sapphire crystal. Don't you wish your cell phone did? I do.
- Corundum is that material on most sandpaper.
- In 2003, 250 tons were man-made.
- If cooled too rapidly, sapphire is more prone to shattering.
- Because of the slow growth process, and very high hardness, most watch crystals are simple slab shapes. The exceptions tend to be very expensive.
- As of 10/2009, you can get single-quantity replacement sapphire watch crystals for $40 or less from Jules Borel.
- Yobokies sells replacements for several Seiko divers for 30-50$.