What Is a Watch Crystal?
The crystal is the transparent cover that sits over the dial. In common usage it’s called the ‘glass’, though only mineral and sapphire crystals are actually glass — acrylic is a plastic. The crystal is held in place by the bezel or pressed into a groove in the case, and it forms part of the water-resistance seal. A cracked or chipped crystal breaks that seal immediately.
The Three Crystal Materials Compared
| Property | Acrylic | Mineral Glass | Sapphire Crystal |
|---|---|---|---|
| Scratch resistance (Mohs) | ~3 | ~5–6 | ~9 |
| Shatter resistance | High (flexible) | Moderate | Low (brittle on impact) |
| Polishable by watchmaker | Yes | No | No |
| Optical clarity | Good (slight distortion) | Very good | Excellent |
| Cost to replace | Low | Moderate | High |
| Common on | Vintage, entry-level, field watches | Mid-range, everyday | Luxury, tool, dive watches |
The Three Crystal Types
Acrylic (Plastic / Hesalite)
Mohs ~3. Acrylic scratches easily — even fingernails can mark it — but this is its strength: scratches can be polished out by a watchmaker, restoring near-perfect clarity. Acrylic is also flexible, so it bends rather than shatters on impact. The original Omega Speedmaster Moonwatch used Hesalite acrylic; it was chosen for space use partly because shattered sapphire inside a spacesuit is dangerous.
Mineral Glass
Mohs ~5–6. Mineral glass is the most common crystal type on everyday mid-range watches. It handles light scratches from daily wear much better than acrylic, but it cannot be polished — once scratched, it stays scratched. It’s also more brittle than acrylic; a hard impact can crack or shatter it.
Sapphire Crystal
Mohs ~9. Synthetic sapphire (aluminium oxide) is second only to diamond in hardness and virtually scratch-proof in normal use. It offers exceptional optical clarity. It’s expensive to produce and significantly more brittle than the other materials — hard concentrated impacts can crack it despite its surface hardness. Standard on luxury watches from Rolex, IWC, and Omega.
How to tell which crystal your watch has: Price is the easiest indicator. Watches under approximately €100–150 almost always use mineral or acrylic. Watches over €300–400 from established brands typically use sapphire. You can also tap the crystal lightly with a fingernail: acrylic sounds dull and plastic-like; mineral and sapphire sound crisper. Anti-reflective coating is applied almost exclusively to sapphire.
Sapphire crystal is scratch-resistant, not shatter-proof. The same hardness that resists surface scratches makes it brittle under concentrated impact. Dropping a watch with a sapphire crystal face-down onto concrete or tile can crack or shatter it completely — a repair that can cost €150–500+ depending on the watch. Don’t assume ‘sapphire’ means indestructible.
Don’t replace a scratched acrylic crystal yet. A watchmaker can polish acrylic back to near-new clarity in a few minutes using a buffing compound. It costs a fraction of a replacement and the result is often indistinguishable from new. Bring it in before spending money on a new crystal.
What to Do If Your Crystal Is Cracked or Scratched
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1Assess the severity — fine surface scratches on acrylic are polishable; deep gouges, cracks, or chips on any material mean the crystal should be replaced. Run your fingernail across the scratch: if it catches, it’s too deep to polish.
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2Protect against water immediately — any crack or chip, no matter how small, breaks the water-resistance seal. Until the crystal is replaced, keep the watch away from water entirely: no handwashing, no rain, no shower.
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3Bring it to a watchmaker — crystal replacement requires the correct diameter, curvature (flat, domed, or double-domed), and thickness for your specific case. A generic fit risks an incomplete seal and future water damage.
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4Discuss the material with your watchmaker — we typically match the original material. However, if your vintage watch has an acrylic crystal and you prefer sapphire, or if you want to restore an original acrylic, we can discuss what’s right for your watch.
Crystal Cracked or Scratched? We Can Help.
Walk into our workshop in Durrës. We carry replacement crystals for a wide range of watches, can polish acrylic crystals while you wait, and will advise on the best replacement material for your specific piece. No appointment needed.
Rruga Aleksander Goga · Durrës 2001 · Albania · +355 67 636 0510
Published by Iglisi Watch · Durrës, Albania · April 2026. Crystal replacement availability depends on case specifications.