SAPPHIRE
Sapphire glass, which is more of a crystal than a glass, is produced from synthetic sapphire. In watchmaking, it is used to make dial glasses. Its high resistance capacity makes it an interesting choice for durable watch glasses.
The sapphire crystal is used for areas requiring visibility in the watch. It can be used for the glass of dials or back. But it can also be used to make more atypical things like a whole case.
Advantages:
The sapphire glass has great characteristics making this material an interesting choice for watch glasses.
Disadvantages:
Sapphire glass is a more expensive material than its direct competitors like acrylic or mineral glass.