Investing in a luxury watch? Lovely! But while movements and materials often steal the spotlight, there’s one feature quietly working overtime to protect your timepiece: the watch glass or crystal.
If you’ve ever admired a watch that still looks flawless after years of wear, chances are it’s because of its sapphire watch crystal. Known for being almost impossible to scratch, sapphire is a go-to material in high-end horology.
But what gives sapphire that incredible toughness? And how does it stack up against other materials?
What Is Sapphire?
What is sapphire glass? While most think of sapphire as the classic deep blue gemstone, in watchmaking, the term usually refers to synthetic sapphire, which is engineered in labs to exacting standards. This synthetic sapphire is crafted into flawless, ultra-clear crystals that protect the watch face.
The use of sapphire crystal in watchmaking is a mark of quality and sophistication. Its hardness ensures that your timepiece remains virtually free of scratches, preserving the flawless view of the dial beneath.
The Mohs Scale of Hardness
The Mohs scale of hardness is a simple, time-tested method for measuring how resistant a material is to scratching. Developed in 1812 by German mineralogist Friedrich Mohs, the scale ranks minerals on a scale from 1 to 10, with 1 being the softest (talc) and 10 the hardest (diamond).
Rather than relying on advanced equipment, the Mohs scale is based on a straightforward principle: a harder material can scratch a softer one. For example, a mineral rated 9 (like sapphire) can scratch materials rated 8 or below but not those rated 10.
Here’s a quick snapshot of key materials on the scale:
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1 – Talc
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3 – Calcite
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5 – Apatite
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7 – Quartz
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9 – Sapphire (Corundum)
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10 – Diamond
This ranking matters more than you might think. In the context of luxury watches, the hardness of the crystal protecting the dial determines how well it resists the scratches of daily life, whether from a stray key, a brushed countertop, or even dust.
Where Does Sapphire Rank in the Moh's Scale of Hardness?
Sapphire ranks 9 out of 10 on the sapphire Mohs scale of hardness, placing it just below diamond, which holds the top position at 10. This high rating means sapphire is one of the hardest materials used in everyday products.
To put it in perspective:
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Quartz, found in common dust and sand, ranks at 7.
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Mineral glass, often used in entry-level watches, ranges between 5 and 6.
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Acrylic (plastic) crystals, the softest option, fall around 3.
Sapphire Durability in Watches and Jewelry
Beauty means little without endurance. That’s where sapphire truly shines. While its hardness makes it exceptionally resistant to scratches, sapphire also offers a high degree of optical clarity, thermal stability, and chemical resistance, making it a top-tier material for both watch crystals and fine jewelry.
Why Watchmakers Choose Sapphire Crystal
Unlike mineral glass or acrylic, sapphire doesn’t haze or scuff with everyday contact. At 9, sapphire is nearly impervious to scratches from anything except materials harder than itself, primarily diamonds or other sapphires. You could brush it across concrete, drop it onto granite, or wear it daily without ever seeing a blemish. It’s this level of near-scratch-proof resilience that has made sapphire the standard for luxury timepieces.
That’s why high-end watches with sapphire crystals maintain their flawless, scratch-free appearance even after years of wear. Whether your watch brushes against a metal railing or rests beside your keys, sapphire keeps the dial beneath crystal-clear and pristine.
Jewelry-Grade Strength, Everyday Reliability
In jewelry, sapphire’s hardness means it can be cut with sharp facets that stay crisp, unlike softer stones that gradually lose definition. Its toughness also means it’s less likely to scratch, though it should be noted that hardness isn’t the same as toughness. A sapphire can still chip or crack under a hard impact, especially along edges or corners.
Caring for Sapphire: What You Need to Know
While sapphire crystal is renowned for its exceptional hardness and scratch resistance, it’s important to remember that hardness doesn’t make it indestructible. Proper care can help preserve your watch’s pristine appearance and ensure its longevity.
Handling and Daily Wear
Sapphire watch crystals are incredibly resistant to scratches from everyday objects. However, they can still suffer from chips or cracks if subjected to sharp, forceful impacts. To keep your watch looking flawless:
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Avoid dropping it or banging it against hard surfaces.
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Be mindful during activities where accidental knocks are more likely.
Sapphire Cleaning
Maintaining the sapphire watch crystal’s sparkle is simple:
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Use a soft microfiber cloth to gently wipe away fingerprints, smudges, and dust.
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For more thorough cleaning, use a mild soap diluted in warm water and a soft brush or cloth.
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Avoid harsh chemicals or abrasive cleaners, which can damage anti-reflective coatings or the crystal surface.
When to Seek Professional Care
If your sapphire crystal does sustain damage---a chip, crack, looseness, for example---have it inspected and repaired by a certified watchmaker. They can replace or polish the clear sapphire crystal, restoring your watch’s elegance and protecting its inner mechanisms.
Conclusion
With a Mohs hardness rating of 9, sapphire offers exceptional resistance to scratches, keeping your timepiece looking pristine through daily wear and beyond. It’s one of the key reasons luxury watches continue to look sharp, clear, and refined for years.
