Modern watch crystals are very advanced, have superior optical characteristics, and are long-lasting. The price difference between the low cost acrylic glass and the most expensive sapphire watch face is considerable.
Because sapphire watch faces are so hard, it is very difficult to scratch the surface. However, it is not impossible if one of the harder materials is used to scratch the surface, and perhaps more alarmingly, if the sapphire watch face is dropped from a height, it may shatter.
Choosing a watch with a suitable watch face is an important cost – benefit analysis. While Sapphire crystal glass will last longer, it is substantially more expensive, and if damaged, it cannot be repaired.
It Is Difficult To Scratch A Sapphire Watch Face
Sapphire measures a score of nine on the Mohs Scale Of Mineral Hardness, making it one of the hardest materials on the planet.
Due to the hardness of Sapphire watch crystal, most manufacturers’ marketing material that describes Sapphire watches tends to refer to them as “deep scratch resistant” instead of “scratch proof.
The reality is that it is not impossible to scratch them.
As seen in the list below, there are twenty one materials with the same or higher on the MOHS Scale Of Mineral Hardness.
Theoretically, a sapphire watch face can only be scratched by a material that has a higher MOHS Scale Of Mineral Hardness score than Sapphire.
Materials that can scratch a sapphire watch face include diamonds and Carbonado.
The full list of materials with an equivalent or higher score on the MOHS Scale Of Mineral Hardness is listed below.
Mohs Scale Of Mineral Hardness
If the watch face is struck with sufficient force, on a rough surface, and at the correct angle, it is possible for a sapphire crystal watch glass to be scratched by a softer material.
An example of the type of event which could scratch the sapphire crystal watch glass is if it is dropped from a height and slides along a hard abrasive surface.
Chipping is also common if it is struck right by a hard angular object.
While Sapphire watch crystal may be hard to scratch, the same cannot be said for its ability to crack.
As with many of the materials with a high score on the MOH scale of hardness, there is often an inverse relationship with brittleness – which means that sapphire watch glass is more prone to shattering.
Sapphire Coated Mineral Crystal Glass
Sapphire-coated mineral crystal glass is a compromise between the convenience of mineral crystal glass and synthetic crystal’s strengths (and expense).
In this process, a layer of sapphire laminate coating is overlayed (laminated) on top of conventional mineral crystal glass.
This produces a product that is scratch resistant but costs much less than Sapphire Coated Mineral Crystal Glass.
Sapphire Coated Mineral Crystal Glass was first commercialized by the manufacturer, Seiko, under the brand name ‘Sapphlex.’
Advantages And Disadvantages
The advantages and disadvantages of Sapphire-coated mineral crystal glass are as follows.
The advantages of sapphire-coated mineral crystal glass.
- Sapphire-coated mineral crystal glass has an Increased tensile strength over mineral crystal glass.
- Sapphire-coated mineral crystal glass with High impact strength.
- Sapphire-coated mineral crystal glass with High flexural strength.
- The product costs less than a sapphire synthetic crystal (sapphire glass)
- The product has good optical characteristics.
The disadvantages of Sapphire coated mineral crystal glass.
- It costs more than mineral and acrylic glass.
- There have been instances when the Sapphire coating has peeled off the underlying mineral glass.
- It cannot be repaired, and if it is damaged, it has to be replaced.
Sapphire Synthetic Crystal (Sapphire Glass)
Sapphire crystal is a synthetic material and is categorized as a crystal.
A crystal is any substance where the atoms/molecules settle into repeating patterns. Most metals and ceramics (including Sapphire) are crystals. I’m sure you could probably produce a “fused sapphire” that had an amorphous structure and thus wasn’t a crystal, but generally, Sapphire is only a crystal.
The first production of synthetic ruby crystals was invented in 1902 in a process called flame-fusion.
The process (Czokhralski process), which produces Sapphire crystals, was first designed in 1916 and commercialized for the production of watch faces in 1960.
The modern method combines the best features of each of the earlier methods.
The method was refined in 1964 into the gradient-freeze technique, where instead of the molten material being withdrawn from the furnace, it is allowed to cool before it is pulled out.
The Sapphire Synthetic Crystal (Sapphire Glass) is produced by mixing crystallizing pure aluminum oxide, by mixing it with “sapphire seed” and placing the uncrystallized Sapphire in a furnace where it is heated to 2,2000C and left to cool for two weeks.
After cooling, the rough raw sapphire crystals are cut into thin paper sheets ready for shaping into the watch face glass.
A diamond saw is used on the grown sapphire crystal to shape them into a watch face, after which it is ground and polished to the finished “glass” product.
Advantages And Disadvantages
The advantages and disadvantages of Sapphire Synthetic Crystal (Sapphire Glass) are as follows.
The advantages of sapphire synthetic crystal glass are:
- It has superior optical characteristics.
- It is incredibly hard and is scratch resistant.
- They can withstand very high temperatures (2030 °C).
- It has an excellent anti-reflection coating.
- It has superior clarity.
The disadvantages of sapphire synthetic crystal glass are:
- It is very expensive.
- It can shatter if hit at sufficient velocity and at the correct angle.
- If damaged, it cannot be repaired and must be replaced.
Conclusion
While sapphire crystal watch faces are resilient and scratch resistant, they are not scratch proof. They can be scratched by materials with a higher MOH score and have been known to shatter if dropped from a height.
