Watch glass, types and characteristics

The watch crystal is one of the most important components of our watches. The glass protects the dial and the hands of the watch, allowing you to observe the time and all its details.

There are two interesting features for watchmaking that vary from one type of glass to another and they are: hardness and impact resistance.

Hardness is the resistance to surface scratches. It is measured using the Mohs scale (1 to 10), with 1 being the least hard and 10 the most scratch-resistant.

The impact resistance indicates the difficulty of breaking the watch glass in an accidental fall or blow.

Plexiglass

These are acrylic glasses made of plastic. It is the most economical range of watch crystals and widely used.

Its main advantages over other types of glass are:

• High impact resistance.
• They are very easy to polish, allowing scratches to be easily removed.

But it also has a big drawback as a watch crystal:

• Low hardness, scratches very easily.

Mineral glass

It is the most used type of crystal nowadays, most of the watches use it.

The advantages of mineral glass over other types are:

• High impact resistance.
• They are very economical.

However, it also has one drawback:

• It has a higher hardness than Plexiglas, but lower hardness than hardened mineral and sapphire.

Hardened mineral glass

Within the mineral crystals, some brands have developed a special type of hardened glass, combining various components, increasing the hardness with respect to the mineral glass.

Its main advantages are:

• They are much cheaper than sapphire crystals.
• Harder than mineral crystals.
• High impact resistance greater than sapphire crystals.

An example of this type is Seiko with her Hardlex and Sapphlex crystals.

Sapphire glass

The main characteristic of sapphire glass is its hardness. On the Mohs scale, which measures hardness from 1 to 10, it reaches the value of 9, which is very difficult to scratch.

The main advantages of this type of watch crystal are:

• It has the highest hardness of all types of glass.
• Great transparency of the glass, allowing the details of the dial and hands to be seen clearly.

But it also has drawbacks:

• It's the most expensive type of crystal.
• It has a lower impact resistance than mineral glass and hardened mineral glass.

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