Sapphire Crystal for Watches: A Deep Dive into its Beauty, Strength, and Application

Over the last century, a variety of materials had been employed to create watch dials. Today, sapphire is most typically used on watches with specific price points. In other words, it's time to let the crystal shine!

Simply put, a sapphire crystal is a transparent cover for a watch face; it’s made of synthetic sapphire, which is a very durable material. It is now coveted in the watch industry for its superior scratch resistance property and clarity. Sapphire gets 9 out of 10 on the Mohs hardness scale, which places it just below diamond; this makes it significantly more scratch-resistant than such materials as mineral glass and acrylic, which are typically used in watch crystals. It may be noted here that the Mohs scale is purely a relative scale, yet it is sufficient for basic hardness measurement. 

A crystal cover works as a protective coating for a watch’s dial and caseback, providing an unimpeded view of the dial's timekeeping features as well as the partially or fully exposed watch movement on the caseback.

History of Sapphire Crystal

A fascinating development rooted in advancements in watchmaking, the use of sapphire crystal in watches dates back to the early twentieth century when French chemist Auguste Verneuil made the first synthetic sapphire. Verneuil invented a procedure known as flame fusion, which employed a flame to melt aluminium oxide powder and gradually deposit it on to a seed crystal. This method enabled the manufacturing of massive, high-quality sapphire crystals.

In the 1930s, Corning Glass Works in New York invented the Verneuil technique, which improved on Verneuil's initial approach and allowed for the production of even larger and higher-quality crystals. This procedure is still used today to make sapphire crystals for watches. Sapphire crystal was initially used in watches in the 1960s, when Swiss manufacturer Omega released the Seamaster 300 model with a sapphire crystal. With manufacturing processes continuing to improve, sapphire crystal became more accessible, and even mid-range watches began to feature it by the 1990s. 

Brands such as Rolex, TAG Heuer, and Breitling integrated sapphire into most of their product lines, emphasising its durability and clarity as the key selling points. Take, for example, the Rolex 1908, which is protected by a domed sapphire crystal with anti-reflective coating; it features a delicate railway minute track around the edge and provides excellent legibility.

Advantages of Using Sapphire Crystal

Sapphire crystal glass is revered in watchmaking because of its strength, clarity, and scratch resistance. It can also be coated to prevent glare. This provides a sharper view of the watch dial and improves legibility, particularly in high lighting conditions. 

As far as its strength is concerned, this crystal can endure slight blows without cracking, and therefore, it’s a shield for luxury, sports, and dive watches in harsh environments. Another reason why watchmakers employ sapphire crystal is that it is commonly associated with high-quality, luxury timepieces. Its application increases a watch's value, and appeals to collectors and aficionados.

Disadvantages of Using Sapphire Crystal

Sapphire crystal has several drawbacks though. To begin with, it is more expensive than mineral glass and acrylic. This additional expense might raise the price of sapphire crystal watches, and this hike is frequently passed on to customers. 

Furthermore, sapphire is extremely scratch-resistant, yet it is also fragile. It is more likely to shatter or crack upon contact than acrylic and mineral glass, which are softer and more impact-resistant. Because sapphire is smooth and clear, it often attracts fingerprints and smudges, somewhat marring its beauty and necessitating frequent cleaning. Sapphire is also denser than, say, acrylic, and hence, a sapphire crystal watch may feel slightly heavier.

How Are Sapphire Crystals Created for Wristwatches?

A highly complex technical procedure is used. Because of the material's exceptional hardness, the resulting ceramic ‘boules’ can only be cut or honed with diamond-studded tools. This also makes further processing of the raw material extremely tedious. Domed sapphire glass is especially expensive since the curve on both sides must be cut into the raw cylinder with diamond cutters. The ultimate high-gloss polish, required for the optical quality of the glass, can only be accomplished with diamond-based grinding pastes; it’s a time-consuming operation.

Despite these challenges, sapphire remains highly popular, especially with regard to high-end watches, due to its durability and premium appearance.

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