Initially made up of glass and then of composite minerals, such as Plexiglas, the watch glass , also called watch crystal , is the transparent part which both allows the indications to be read and protects its constituent parts.

There are three types, here they are:

Acrylic glass - This is an economical type of plastic-based glass. It has the ability to reflect reflections less and therefore allows good visibility of the dial. However, it is less resistant to scratches and then to breakage. Its hardness index (Vickers) which is the hardness index of a material, is 500. Which is therefore the lowest.

Sapphire glass - This is the most resistant glass in terms of scratches, shocks or breakage. Its Vickers hardness index is equal to 2300 (second hardest component after diamond). More expensive than other watch crystals, it is created in the laboratory from aluminum oxide and can be treated with an anti-reflective or anti-scratch coating.