When you want to acquire a watch, we can be interested in the glass which composes it. In watchmaking, there are three categories of watch glass; acrylic glass, mineral glass and sapphire glass. What are the differences between these 3 watch glasses used in the watch industry?In this article, we are going to present their specificities, their advantages and their possible disadvantages.
Acrylic glass is a glass derived from plastic commonly referred to as plexiglass. The advantage of this type of glass is that it is extremely light and economical. However, it is not very impact resistant and breaks easily. It is also scratched much more easily than other types of glass, but it is easy to polish it again. Acrylic glass has a Vickers hardness of 500 which remains relatively low, the hardness of Vickers being an index measuring the solidity of the materials.
Mineral glass is a much more robust glass than acrylic and is the glass most used in watchmaking. It is a glass in the classic sense of the word, in the sense that it is not a chemical compound. Mineral glass, although heat-treated to be scratch resistant, may, due to high friction, get scratched. Unlike acrylic glass, mineral glass will be more complex to be polished again, it will then be necessary to change the entire glass. Likewise, in the event of a severe impact, this type of glass can break even though this is not common. Mineral glass has a Vickers hardness ranging from 650 to 800. In short, mineral glass is a robust glass but it can deteriorate after a few years.
Sapphire crystal is a compound that is created in the laboratory. More expensive to produce than the glasses studied previously, sapphire crystal is obtained fromaluminum oxide crystallized at very high temperature (2050 ° to be precise), it therefore has the same chemical properties as natural sapphire. Thanks to its chemical properties, sapphire crystal is a very hard and resistant component (Vickers hardness equal to 2300), it is the second hardest component after diamond. For comparison, it is also 7 times harder and stronger than hardened steel. Thus the sapphire crystal is a glass which breaks or is very difficult to scratch.
At Charlie Paris, all our mens watches as well as all our automatic watches for women are equipped with a sapphire crystal, in order to guarantee them the best possible longevity. It should be noted that the thickness also comes into play on the impact resistance of the glass of a watch. The thicker the glass, the stronger it will be. On our sport models, we therefore chose to offer them with a thicker sapphire crystal than on our city models.
WARNING ! Just because the glass on your watch is very durable doesn't mean the interior is too. Thus, if you drop your automatic watch which has a sapphire crystal, it will appear intact from the outside but the cogs of the movement may have been damaged as a result of the shocks. You should then go to your watchmaker to have it serviced. It is important to have a watch with quality glass, but that shouldn't prevent you from treating your watch with the utmost care!
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