When you are going to buy a watch then you will notice that there is a lot of choice regarding watch glasses that are used.
In this blog I want to reflect on the types and which is particularly interesting when you buy a new watch. Watch glasses exist in all kinds of hardness and materials. In combination with all forms of glasses, a profession in itself.
Here is the most common information about watch glass.
Plastic / Plexiglas
This so-called unbreakable glass was developed in the First World War. Made of celluloid, it had its drawbacks: it was gray in color, susceptible to scratching and very quickly deformed in heat. To place it, it was brought into a vaulted form with a press and placed under tension in the rebate, as is currently the case. Because of the disadvantages of this glass, this has been further developed.
Another development in 1934 was acrylic glass (brand name: Plexiglas), which was preformed in the factory. Advantages were a better fit, clear as glass and relatively harder than celluloid. Due to the greater elasticity, it is easy to deform and install. A disadvantage is the water resistance of watches. Another disadvantage is distortion under the influence of temperature change: if the plastic glass expands more than the surrounding metal of the cabinet, it can crack. Conversely, disproportionate shrinkage can affect water resistance. This problem was solved by applying a metal tension ring in the inner edge of the plastic glass, which ensures a better seal against dust and water. Plexiglas is a soft material and therefore very sensitive to scratches. The advantage is that you can easily polish out scratches and replacing Plexiglas is easy and cheap for a watchmaker to do. This glass also gives the dial a warmer authentic glow. Plexiglas is actually not used much anymore. You often come across them with vintage watches, such as old vintage Invictas that actually use all of this. But there are exceptions:
A good example is the first watch "on the moon": the Omega Speedmaster. This is still equipped with a plastic glass. The reason? Otherwise it would break into small dangerous pieces on the moon! Plastic glass does not break so quickly, and if it does break, then not into small pieces such as sapphire glass and mineral glass.
The next is mineral glass, which is about seven times harder than plastic glass and is used with most watches. Mineral glass is made from glass crystals that have been heated or chemically treated, making them harder to become more scratch-resistant. This glass is not the most scratch-resistant on the market, but you have to do your best to make it crack or shatter. Although there is not much difference between mineral and sapphire glass, the latter is more expensive to purchase. When your watch needs to be replaced, this is not expensive in most cases. This is also the reason why many brands choose to use this for their watches.
Sometimes people try to make this glass even harder with a coating, making the glass more scratch-resistant.
Sapphire glass is three times harder than mineral glass and is therefore slightly under diamond. Sapphire glass is widely used in watches from the top segment and it is therefore logical that this is the most expensive glass on the market. Sapphire glass is scratch resistant and can take a beating. In fact, you can only really scratch it with other hard materials such as diamond or other hard rocks. With sapphire glass you can quickly think that it is natural sapphire crystals, this can be misleading. They use a synthetic fabric with the same properties for watches. Sapphire glass is clear and very reflective, which is why sometimes an anti-reflective coating is used. You have to take into account when this coating is used on the outside of the glass that it is not as hard as the glass itself and can therefore be damaged.
Although sapphire glass offers good protection against scratches, it can break faster than mineral glass. Replacement costs more than a new mineral glass.
Invicta has found a combination that combines the scratch resistance of sapphire and the impact resistance of mineral glass and has been using it in many of its collections for years. But what is it anyway? Flame Fusion Crystal comes about after a process in which synthetic crystal is produced under high pressure and temperature. This synthetic sapphire that is developed with the help of oxygen and hydrogen by melting different minerals. The end result is a synthetic sapphire that, in terms of toughness and durability at a lower cost, corresponds to real sapphire. The glass is impact-resistant due to the mineral glass that forms the basis and scratch-resistant due to the sapphire. In addition to this Flame Fusion process, Invicta also adds other tricks to the glass of some watches in some of its models. These are equipped with glass that colors along with the light, which of course has a beautiful effect.
No matter how beautiful these developments are, you always have to take one thing into account:
"No matter how hard a glass is, glass can always break ...!"