What type of glass should you choose for your watch?

In watchmaking, there are three main types of glass: plexiglass, mineral glass and sapphire glass.
Each type of glass has its own set of advantages and disadvantages and that is exactly what we are going to discover today.

Plexiglass or acrylic

We'll start with the most common on vintage wristwatches, the famous plexiglass or acrylic.

This glass is made of plastic, it offers great resistance to shocks thanks to its malleability but does not resist scratches well.
The advantage is that this material is very easy to polish, so you can often remove those nasty scratches.

Some brands that use this type of glass on certain models offer to polish the plexiglass of your watch for free if they visit the store.

To conclude, one last positive point of acrylic is its price: it is much cheaper than its competitors.

Mineral Glass

This glass is used on modern waterproof watches because it is much harder and therefore scratch resistant than plexiglass. The downside is that it is easier to break than the previous glass and it is more complicated to polish.

The cost of this mineral glass is between that of plexiglass and sapphire glass.

Sapphire glass

Sapphire glass is surrounded by mysteries. It is said to be unbreakable and scratchproof, but is it true?

This is not entirely true, it is very difficult to scratch, on the other hand it remains very fragile.
In fact, it is made of synthetic corundum, more precisely synthetic sapphire and has a hardness of 9 on the Mohs scale. This scale measures the hardness of a stone. So the only thing that can scratch the glass is another sapphire (corundum) or a diamond which is 10 on the Mohs scale (it is harder).

However, while very scratch resistant, it is very sensitive to shocks and can break quite easily. Of all the types of glass we have seen, it is by far the most fragile and also the one that reflects the most light.

To prevent watches from reflecting too much light, an anti-reflective coating is used. The disadvantage of this anti-reflective coating is that it can scratch easily. Treatments can then be used on the inside of the glass.

To conclude on this sapphire glass, it is significantly more expensive than mineral glass, especially when it has special curvatures such as a double domed glass for example.

So, which glass should you choose?

Generally you don't have a choice, the glass is not interchangeable on your next watch, so you go with the type of glass that the brand has chosen. The advantage is that you now know the differences between these 3 main types of glass and you will no longer have any surprises on a daily basis!

To summarize:

• Acrylic glass / plexiglass: Vintage watch, resistant but easily scratched

• Mineral glass: Entry level, the most complete

• Sapphire crystal: High-end, fragile virtually scratch-proof in daily use