Sapphire is worth paying for. It is the part of a watch you look through every time you check the time, and it is the part most likely to pick up damage that you cannot ignore. A sapphire crystal is why a five-year-old watch can still look new.
What the three materials are
Acrylic is plastic. It is cheap, it will not shatter, and light scratches can be polished out at home. It also scratches if you look at it wrong. Mostly found on vintage watches and inexpensive modern ones.
Mineral glass is hardened glass. Far more scratch-resistant than acrylic, considerably less so than sapphire, and it cannot be polished, so scratches are permanent.
Synthetic sapphire is grown in a furnace from aluminium oxide, the same material as natural sapphire. On the Mohs scale it sits at 9, second only to diamond at 10. In practice that means the ordinary things that scratch a watch, door frames, desk edges, keys, stone worktops, do not mark it.
So why does anyone still use mineral glass?
Cost, mostly. Sapphire is harder to grow, harder to cut and harder to shape into a domed or boxed profile.
There is also a real trade-off. Sapphire is hard, but hardness and toughness are not the same thing. Very hard materials tend to be brittle. A sharp impact that would put a scratch in mineral glass can chip or crack sapphire outright. In everyday wear this almost never happens, and scratches are far more common than impacts, which is why sapphire wins for most people.
What about "sapphire coated"?
Sapphire coated glass is mineral glass with a thin sapphire layer applied to the surface. It sits between the two in both price and performance. It resists light scratching better than bare mineral glass, but the coating is thin, and once it wears through the glass underneath behaves like glass.
It is a legitimate middle option and it should be described honestly. If a specification says sapphire coated, it is not the same thing as a solid sapphire crystal. Every Claude Bernard product page states which one the watch carries.
Anti-reflective coating
Sapphire reflects more light than glass, which is why many sapphire crystals carry an anti-reflective treatment on the inside surface, sometimes both. Inside-only coating is more durable, since the coating cannot be scratched off. Both-sides coating gives better legibility in bright light but is more easily marked.
If you have ever seen a watch photograph with a faint blue or violet cast across the dial, that is the anti-reflective layer.
How to tell what you are looking at
Check the specification rather than guessing. If you have the watch in hand, a drop of water beads tightly on sapphire and spreads more on mineral glass, and sapphire feels colder to the touch because it conducts heat away faster. Neither test is conclusive. The specification is.
Does it affect resale?
Indirectly, and significantly. A scratched crystal is the single most visible sign of age on a watch, and replacing one costs money. A watch that has kept a clean crystal for a decade simply presents better.
Common questions
Can a scratched sapphire crystal be polished?
Not practically. Sapphire is too hard to polish with normal materials, so a marked sapphire crystal is replaced rather than repaired. This is rare, because it is difficult to scratch in the first place.
Is sapphire unbreakable?
No. It is highly scratch-resistant, not impact-proof. A hard strike on the edge can chip it.
Is a domed crystal better?
It is a design choice. A domed or boxed crystal gives the dial depth and a warmer look, at the cost of more reflection from certain angles.
Which Claude Bernard watches use sapphire?
The crystal is listed in the technical specifications on every product page, under Glass. Both sapphire crystal and sapphire coated glass appear across the range, so check the reference you are looking at rather than assuming by collection.