They can be made of any of three materials: 1- plexiglass (a clear, lightweight type of plastic), 2- ordinary glass - like that used for windows, and usually referred to in the watch business as "mineral glass" or 3- synthetic sapphire (see question 4). Some crystals are made of both mineral and sapphire glass. Seiko, for example, makes some watches with crystals made of mineral glass covered with a layer of synthetic sapphire - (
Master Moon). Seiko calls this composite material "Sapphlex"
.
What are the advantages and disadvantages of each material?
Plexiglass, as you would expect, is the least expensive. It is also the least likely to shatter and the most likely to become scratched. Mineral glass, even though it has been hardened by a tempering process, is more likely to break than plexiglass. But it is also more scratch-resistant than that material - (
seiko divers watches). Synthetic sapphire is the most expensive glass crystal material and the most scratch resistant
. Because it is so hard, it is also brittle, and shatters more easily than mineral glass or plexiglass.
