Component record · Case
Crystal (Glass)
VerifiedThe transparent cover, historically glass and today also acrylic (plastic) or synthetic sapphire, that protects the dial and hands while allowing them to be read.
What it does
Shields the dial and hands from dust, moisture and impact while remaining optically clear.
How it works
Mineral glass is inexpensive and reasonably scratch-resistant but can shatter on hard impact; acrylic is highly shatter-resistant and can be polished to remove minor scratches, but scratches easily; sapphire crystal is extremely scratch-resistant (second only to diamond in hardness) but more prone to shattering under sharp impact and is costlier to produce.
Crystals may be flat, domed, or fitted with a magnifying 'cyclops' lens over the date window; anti-reflective coatings are commonly applied to sapphire and some glass crystals to reduce glare.
Evolution
From glass, to acrylic in mass-market and sports watches of the mid-20th century, to sapphire becoming a mark of quality and durability in watchmaking from the later 20th century onward.
Known variations
- Flat crystal
- Domed crystal
- Cyclops (magnifying) crystal over a date window
- Anti-reflective coated crystal
Identification for collectors
- Fine, buffable scratches suggest acrylic; a crystal that resists scratching from a steel implement suggests sapphire; shattered glass fragments (rather than cracks) suggest mineral glass
Common failure modes
- Scratching (acrylic) or shattering (glass or, less often, sapphire under sharp impact)
- Cracking from thermal shock or case flexing
- Delamination of anti-reflective coatings
Photographs
Photographs are illustrative examples of the type, not necessarily the exact object described. Verify details against the source file page.
Sources & references
- de Carle, D., Watch and Clock Encyclopedia
Where sources disagree, the disagreement is stated rather than resolved silently.