What is sapphire glass?

Glass... or sapphire? Why not both! Sapphire glass is used in the best timepieces ever, thanks to its transparency and great durability. Let's discover together what sapphire glass is.

A bit of background…

It is a resistant and hard material, very prestigious. It is made, in fact, of sapphire, or rather Corundum, a mineral composed of aluminum oxide. We usually find it in jewelry, with its gems in various colors. It is important to remember that the different shades are due to the presence of impurities, such as hematite or rutile. Natural sapphire/corundum is actually transparent.

There is also synthetic sapphire, thanks to the creation of the French chemist Auguste Verneuil, who lived between the mid-1800s and early 1900s.

What to choose?

As we have seen, sapphire glass is usually chosen for luxury timepieces. However, it is not the only material used for watches. Let's look at the alternatives.

Acrylic

It is the cheapest material but also the most prone to scratches. A positive aspect of acrylic is that it can be polished back to shine very easily. It has high resistance to impacts and pressure. Compared to glass, it does not shatter. It is preferable in sports watches or those requiring great durability.

Mineral glass

It is, in fact, a traditional glass that undergoes a chemical treatment to improve scratch resistance. It has a low cost, although higher than acrylic. It is a true middle ground between the other two materials.

Sapphire glass

Definitely the best for scratch resistance and toughness, it is unlikely to show cracks due to impacts. Unfortunately, the downside is that if it suffers a strong impact, it tends to shatter. It has a higher cost compared to the other two materials.

It has a hardness superior to mineral glass and, on the Mohs scale, which measures the hardness of materials, it is second only to diamond. It can therefore only be scratched by diamond.

A curiosity

Although it is difficult to trace the history of the use of sapphire glass in watchmaking, it seems that around 1930 it was used by Jaeger-LeCoultre on some Reverso models, very popular watches. From the 1960s, it gained more fame with the first Rolex watches with sapphire glass: these are the Perpetual Date ref 1530, Perpetual Datejust ref 1630, and Oysterquartz.

Since the mid-1990s, sapphire glass has been the choice of Rolex for all new watches. Today the brand also treats it with scratch-resistant and anti-reflective coatings to make the dial of its watches perfect in every detail.

 

It is therefore the preferred material of the best brands, thanks to its durability. It protects what it covers, ensuring its visibility. A true jewel of watchmaking, waiting to be discovered.