About watch glasses
Every wristwatch, simple or complicated, is subject to the influence of the environment. Protection from sudden temperature changes, moisture and dust is a watch glass. It also allows you to protect from the mechanical damage the dial and arrows. Watch companies use three main types of glasses: sapphire, plastic and mineral, which differ in their characteristics, quality and price.
The simplest is plastic glass. Mineral glass is more popular, therefore it has the most democratic value. The most expensive is sapphire glass, while it is more high-quality. It is possible to install any glass in the watch, but according to its characteristics it must correspond to the class of the device itself. For example, sapphire glasses are installed in waterproof and shock-resistant models, and plastic or mineral ones in everyday or sports watches. And the reason for this decision is the price policy.
Mineral glass is the most common, as its production and replacement is inexpensive. But, it is worth noting that the strength of this glass is quite good - 6.5 units on the Mos's scale. Artificial sapphire glass is considered the most solid and reliable protection of the dial, but in production and replacement it is the most expensive. Its price determines not only the material, but also the form, since it is not so simple to make a complex product out of sapphire. Hardness is close to diamond: its strength is 9 units. Plastic glass is not glass in its essence. This is a kind of protection of the dial, the strength of which depends on the type of this material.
The shape of the glass depends not only on the designer's creative impulse, but also on the type of watch. The main forms are round and curly. Design models usually use the latest: oval, faceted, rhombic or square. For sports watches, glass of round or rectangular shape is used most often. Flat and convex glass is also quite common. Flat is easy to replace, but it is strong enough. Glass convex form is found in sports models. It is also reliable, due to the increased thickness.
How to distinguish one type of glass from another? Usually the inscription on the dial indicates the type of glass: Sapphire glass - sapphire, Srystal - mineral, and Hesalite - plastic. If there is no inscription, you can use the following test. On the surface of the glass to drip a little water, if the glass is mineral, then the drop with the inclination of the watches will spread with a tail, and if sapphire, it will remain round. If the glass with anti-reflective coating, the drop does not move at all from the surface.