Domed Sapphire Glass

The Best Watch Crystal in the World

Have you ever been annoyed by a broken phone display or watch glass? Have you ever wondered why manufacturers do not use more resistant materials? The answer is easy, many manufacturers are using cheaper and less qualitative components for their products to save costs and time with the aim to maximize their profits.

During the development process of the Novum, we analyzed thoroughly all available materials and qualities. Having insider knowledge now, we want to give you some insights into the confusing world of watch glasses by explaining the different materials with their advantages and disadvantages to you. After reading this article, we believe that you understand why a pure domed sapphire glass – the best watch glass in the world – matters.


There are various materials used for watches that are labelled as “glass”. For example, plastics, mineral glass, sapphire coated mineral glass and pure sapphire crystal.

Mineral glass

We have to distinguish between untreated and tempered mineral glass. The chemical name is silicon dioxide (SiO2). Rock crystal and smoky quartz are closely related to mineral glass. By adding different oxides, such as aluminium oxide or boric oxide, mineral glass can be refined. This leads to better scratch resistance and hardness. In general, mineral glass is harder than plastic, it is neither osmotic nor does yellowing occur.

Though scratches cannot be as easily removed through polishing and the material can break. In the worst case, it splinters and can damage the movement and injure the person wearing it.

Mineral glass coated with a thin layer of sapphire

To compensate for the disadvantage of mineral glass, many manufacturers use mineral glass with a thin laye of sapphire, as this is only marginally more expensive. Erroneous, they often claim to have a ´sapphire glass´, which leads to significant misinformation of customers. The quality differences are huge compared to a pure sapphire glass. Therefore, when you are looking for a watch, you should always keep an eye on the type of sapphire glass that is used.


As indicated by the name, the material consists of a plastic named polymethyl methacrylate (short: PMMA). This plastic is better known by the names Perspex, acryl glass, or hesalite glass. The main advantages of these materials are: They are very lightweight, relatively impact-resistant, easy to polish and quite cheap. The major disadvantage, given by the low density, is the significant vulnerability for scratches. UV rays and time may lead to yellowing of the material. Moreover, due to its osmotic characteristics, it can also be slightly water-permeable.

Pure sapphire glass

Our foundation is quality and we will never compromise on that. That is exactly the reason why we use pure sapphire glass for every single TOMHOLM Novum. For good reasons, we are willing to pay the higher price:

Although sapphire glass is transparent, the name “glass” is misleading. Sapphire glass contains a crystalline structure which makes it highly scratch-resistant. After the moissanite and the diamond, it is the third-hardest transparent material on the planet. Sapphire glass is made out of a pure synthetic sapphire (monocrystalline) which is produced from melted aluminium oxide (Al2O3). The production creates huge crystals which are cultivated by the means of electrolysis. Subsequently, the crystals are divided into slices and the shape of the watch glass is later time-consumingly cut out of these slices.

In addition to the remarkable aesthetics, the curved shape of the TOMHOM Novum's sapphire glass provides the advantage that any external forces are deflected more easily to the sides. This leads to even higher production costs because the watch glass has to be cut out of a block, but the additional resistance to external impacts is outstanding and in our opinion worth the expenses.

Consequently, domed sapphire glass is the best watch glass in the world. It might only break if extreme forces are encountered and can only be scratched with a diamond or moissanite. If you encounter any scratches on your sapphire glass, they are probably caused by aluminium and can be easily removed with a rubber.  

During the product development, we performed several quality tests with the Novum. Besides to usual industry tests, we go one step further and permanently strive to raise the bar in order to be the best. Our watches survived extreme temperature, ice, scratch and high impact tests - without any damage to the movement or sapphire crystal.

These tests encouraged us to pay the higher costs for a pure domed sapphire crystal in order to provide you with a sustainable and reliable watch of premium quality.