Sapphire

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.

Fun facts

• 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.

See also

• AR coatings.
• crystal

Links

• Yobokies sells replacements for several Seiko divers for 30-50$.

Related pages