Why watches have sapphire crystal...

by Zhang Ron on Feb 21, 2024

Why watches have sapphire crystal...
Watches come in a wide variety of sizes, designs, and materials, making each timepiece unique. However, one common feature that stands out is the use of sapphire for the watch crystal, the protective window over the dial. Sapphire has become the standard for luxury watches, much like tempered laminated glass is the baseline standard for car windshields.

But how did sapphire become so integral to watch manufacturing? And what materials were used before its introduction? Furthermore, what sets different types of sapphire crystals apart, and are there any other materials used in the watch industry besides sapphire? Additionally, is sapphire used for anything else in the realm of watches?

Surprisingly, that little lens on your watch dial is made from one of the hardest substances on Earth. Sapphire is one of the two precious gemstones derived from the mineral corundum, with the other being ruby. Corundum, which is crystallized aluminum oxide, is naturally clear. The blue color of sapphires and the red color of rubies come from impurities, such as traces of titanium and iron for sapphires and chromium for rubies. Sapphire boasts a rating of 9 on the Mohs Hardness scale, surpassed only by moissanite at 9.5 and diamond at a perfect 10. It is essentially scratch-proof, making it an ideal material for watch crystals that are prone to encounters with hard surfaces.

Sapphire has been used in watchmaking since 1902 when French chemist Auguste Verneuil developed a process to create synthetic crystals and rubies. Synthetic rubies quickly found their place in watch movements as friction-reducing ball bearings, replacing the more expensive natural jewels. However, sapphire crystals only appeared sporadically on certain watch models until the 1970s. The first watch believed to have a sapphire crystal was the Jaeger-LeCoultre Reverso in the 1930s, while Omega started using sapphire crystals on some of its watches in the 1950s. Brands like Rado, Enicar, and Rolex also adopted sapphire crystals during this time, considering them an upgrade over their predecessors.

Traditionally, three materials have been extensively used for watch crystals: acrylic, mineral crystal, and sapphire. Each material has its own unique characteristics and drawbacks. Acrylic, also known as Plexiglas or Lucite, is a durable and impact-resistant plastic. It offers high optical clarity, dimensional stability, and is lighter and more shatter-resistant than glass. Acrylic crystals are still used in many affordable watches today, including the iconic Omega Speedmaster. However, with a hardness rating of only 3 on the Mohs scale, the need for a tougher and more scratch-resistant alternative became apparent.

Mineral glass, made from silica in a process similar to tempered glass, emerged as a more scratch-resistant option. It is more transparent than acrylic and significantly harder. While mineral glass is less reflective and relatively inexpensive compared to sapphire, it is more prone to scratches. Seiko's Hardlex material, a type of mineral glass, is commonly used in their lower-priced mechanical watches.

Rolex's adoption of sapphire crystals in the early 1970s paved the way for other luxury watchmakers to follow suit. Sapphire offered undeniable benefits, including extreme hardness and scratch-resistance. Despite its higher production costs and susceptibility to shattering under extreme impact, sapphire crystals became the preferred choice for most watchmakers and consumers. Technological advancements in horology, such as the use of anti-reflective coatings, helped address some of the challenges associated with sapphire crystals. These coatings significantly reduce glare and enhance dial readability.

While sapphire crystals have become the standard for high-quality watches, some brands are exploring alternative high-tech materials for their economical and aesthetic advantages. Large manufacturers like Timex and microbrands like Vortic have used Gorilla Glass, a material developed by Corning, for their watch crystals. Gorilla Glass offers similar hardness to sapphire but is more shatterproof, making it a popular choice for display screens on various devices. Most sapphire crystals are finished with an anti-reflective coating on at least one surface to reduce glare. Applying the coating on both the inside and outside surfaces eliminates glare but may increase the risk of scratches on the outside.

Depending on the watch's purpose, sapphire crystals can be domed, flat, or extra-thick. Domed crystals reduce light distortion, ensuring legibility in different environments, while flat crystals help reduce overall thickness and weight. Some dive watches, designed for extreme depths, feature extra-thick sapphire crystals. Sapphire is not only used for crystals but also for the dials of skeleton watches, as they provide a transparent surface to showcase the movement. In recent years, a few watchmakers have even experimented with sapphire cases, pushing the boundaries of innovation and design.

In conclusion, sapphire has become an indispensable material in watch manufacturing due to its exceptional hardness and scratch-resistance. While other materials like acrylic and mineral glass havetheir own advantages and are still used in certain watches, sapphire crystals have become the standard for luxury timepieces. The use of sapphire provides durability, clarity, and a touch of luxury to watch dials, enhancing the overall aesthetics and longevity of the timepiece.