Sapphire crystal on watches: almost scratch-proof… but not indestructible

For more than thirty years, it has been said in the watch world that sapphire crystal is
"scratch-proof." It sounds logical: sapphire is, after all, one of the hardest
materials known to us and is even used in high-tech applications
such as lasers and military optics. But anyone who wears watches long enough knows
that the reality is a little more nuanced.

Sapphire crystal is extremely scratch-resistant, but not immune to damage. In this
article, we explain how daily use can still cause scratches or damage
and how this can easily be prevented in practice, without compromising the
design of the watch.

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What makes sapphire crystal so strong

Sapphire crystal on watches is synthetic sapphire: crystalline aluminum oxide (corundum), which scores 9 on the Mohs hardness scale. Only diamond (10) and a few very hard industrial materials are even harder.

Therefore, sapphire can effortlessly withstand almost everything we touch daily, such as keys, metal objects, tables, and coins. For many wearers, sapphire thus seems "unscratchable", and in normal circumstances, this is indeed true.

But sapphire doesn't only have strengths; it also has limitations.

How sapphire crystal can still be damaged in everyday life

1. Sand and Dust: Small Particles, Big Effect

At the beach, in the garden, or at work, watches come into contact
with grit and sand particles. Much sand consists of quartz (hardness 7), which is not
harder than sapphire itself. But sand also contains impurities:
small pieces of mineral particles, sometimes harder than 9, which under the right pressure
or shearing motion can leave micro-scratches. These scratches are often
subtle but visible in bright light.

2. Unassuming Culprit: The Anti-Reflective Coating

Many modern watches have an anti-reflective (AR) coating. Ironically, this layer is much softer than the sapphire itself. As a result, most damage perceived as "scratches in the sapphire" turn out to be scratches in the coating. This is also why some watch manufacturers opt for only internal AR coating; the outermost layer is simply more vulnerable.

3. Indirect Contact with Diamond or Industrial Materials

The sapphire crystal does not need to come into contact with a diamond itself to be at risk.

A rough surface containing diamond dust, silicon carbide, or other industrial
abrasives can cause a scratch with a single movement.

This occurs particularly in:

  • workshops
  • construction sites
  • gym bags also containing jewelry
  • studio or hobby environments.

4. Point Load and Impacts: Sapphire is Hard, but Brittle

Hardness is not the same as toughness. Sapphire is extremely hard, but also brittle. A hard, (targeted) impact, for example against a curb, door handle, or metal workbench, can cause chipping or cracking. This is not a scratch, but a small fracture along the edge.

  • How do you recognize if it's really a scratch?

    • Does the damage feel rough or does your nail catch a little? → true scratch or chip.
    • Is the spot dull, milky, or purple/blue at a certain angle? → likely AR coating damaged.
    • Do light lines disappear after polishing? → not a scratch, but dirt or a coating problem.

  • Can you remove scratches from sapphire crystal?

    In practice: hardly. Sapphire is so hard that polishing rarely works; usually, the entire crystal needs to be replaced (read more about polishing here). Therefore, prevention is the best strategy.

Many watch enthusiasts think that a screen protector on sapphire is a "waste" because it would detract from the design. Modern protectors, however, prove otherwise:

Benefits of a crystal protector

  • Completely transparent: Crystal clear despite the layered structure. The subtle color nuances, the depth of a dial or the elegant curve. Everything
    remains exactly as intended.
  • Invisible after installation: custom-made for each watch.
  • Protects against scratches in sapphire and coating.
  • Inexpensive to replace, unlike sapphire crystal.
  • No impact on the function of the dial, bezel or AR effect.

In practice, most wearers don't notice it until a deep scratch could have occurred.

Conclusion

Sapphire crystal remains one of the best choices for high-quality watches. It is exceptionally scratch-resistant, clear, and durable. However, it is not "unscratchable." Daily use, grains of sand, industrial particles, AR coatings, and hard impacts can still cause damage. With a subtle Chaperon crystal protector, both the sapphire and the watch remain perfect, without altering the appearance, and without
the fear of that one scratch that does stick.



Find a screen protector for your watch here