A watch crystal is the transparent protective cover above the dial normally encased by the bezel on top. Almost all of today’s timepieces feature watch crystals made of Mineral Glass, Plexiglas or Synthetic Sapphire.
Mineral glass has been widely used on timepiece crystals since the late 19th Century on pocket watches, throughout the 20th Century on wristwatches and is still featured today on popular timepieces. Mineral glass is inexpensive, more durable and harder than standard glass and is presented on many affordably priced watch styles. Mineral crystals however, are not scratch-resistant and are prone to become easily scratched, especially on the top surface of a wristwatch.
There are buffing compounds available that are capable of removing light scratches on mineral crystals and diminishing the appearance of deep-set scratches on mineral crystals.
Plexiglas is a clear lightweight plastic featured on many wristwatches in the mid to late 20th Century and is still featured today on many digital and sport watches. Plexiglas is both shatter-proof and shock resistant. It is considerably less expensive than mineral and sapphire crystals. However, Plexiglas crystal can be easily scratched and the scratches cannot be readily removed.
A sapphire crystal is a synthetic man-made substance that has characteristics identical to the natural gemstone sapphire. Sapphire crystals are highly resistant to scratching. Sapphire crystals are extremely strong, three times harder than mineral crystal and as durable as genuine sapphires.
Select watchmakers Invicta, Seiko, Swiss Legend and Lucien Piccard offer their own trademarked variations of sapphire crystals: Flame Fusion™, Hardlex™ and Sapphitek™ respectively. Each of these crystals feature production processes similar to sapphire crystals and are considered be more durable and scratch resistant.
Some sapphire crystals feature anti-reflective coating on both sides that reduce glare and increase the legibility on the dials.