Sapphire glass, mineral or acrylic, which glass to choose for your watch ?

When one wishes to acquire a watch, We can consider the type of glass it is made of. In watchmaking, there are three categories of watch glass: acrylic glass, mineral glass, and sapphire glass. What are the differences between these 3 watch crystals used in the watchmaking industry? In this article, we will present their specific characteristics, their advantages, and their potential disadvantages. 

• Acrylic watch glass or Hesalite glass: Acrylic glass is a type of glass derived from the plastic commonly known as Plexiglas. The advantage of this type of glass is that it is extremely lightweight and economical. However, it is not very impact-resistant and breaks easily. It also scratches much more easily than other types of glass, but it is easy to polish again. Acrylic glass has a Vickers hardness of 500 which remains relatively low, the Vickers hardness being an index measuring the strength of materials.
• Mineral watch glass: Mineral glass is much more robust than acrylic and is the most widely used glass in watchmaking. It is glass in the classic sense of the term, meaning it is not a chemically produced compound. Although mineral glass is heat-treated to be scratch-resistant, it can still be scratched by significant friction. Unlike acrylic glass, mineral glass is more difficult to polish, and in such cases, the entire glass must be replaced. Similarly, in the event of a significant impact, this type of glass can shatter, although this is not common. Mineral glass has a Vickers hardness ranging from 650 to 800. In short, mineral glass is robust but can become damaged after a few years.  
• The sapphire watch crystal: Sapphire glass is a compound that is created in the laboratory. More expensive to produce than the glasses studied previously, sapphire glass is obtained from...aluminum oxide Crystallized at a very high temperature (2050°C to be precise), it therefore possesses the same chemical properties as natural sapphire. Thanks to these chemical properties, sapphire crystal is a very hard and resistant material (Vickers hardness of 2300), making it the second hardest material after diamond. For comparison, it is also seven times harder and stronger than tempered steel. Thus, sapphire crystal is extremely difficult to break or scratch. 

Watch glasses at Charlie Paris

At Charlie Paris, all our watches Automatic watches are equipped with sapphire crystal to ensure maximum durability. It's worth noting that the thickness also affects the impact resistance of a watch crystal. The thicker the crystal, the stronger it will be. On our sport models, We have therefore chosen to offer them with a thicker sapphire glass than on our city models.

ATTENTION ! Just because your watch crystal is very resistant doesn't mean the internal mechanism is as well. So, if you drop your automatic watch with a sapphire crystal, it may appear intact on the outside, but the movement's inner workings could be damaged by the impact. In that case, you should take it to your watchmaker for servicing. It's important to have a watch with a high-quality crystal, but that shouldn't stop you from treating your watch with the utmost care!