What it is
Watchmaking ceramic is zirconium dioxide (ZrO₂) sintered at high temperature into a dense, hard, fine-grained material. Variants include yttria-stabilised zirconia (the standard luxury-watch ceramic) and silicon-nitride composites. The material is significantly harder than steel (Vickers ~1300 vs steel ~200), almost completely scratch-resistant in normal wear, and colour-stable across UV and chemical exposure. The trade-off: it's brittle to impact, with hard impacts producing fracture rather than dent.
What it's used for
Bezels: the most common application. Rolex Cerachrom (since 2005, full Cerachrom on Submariner / GMT-Master / Daytona); Omega ceramic bezel (since 2007); IWC Da Vinci ceramic bezel (1986, the original luxury ceramic application). The bezel insert holds the engraved 60-minute (or 24-hour for GMT) markings; the colour can be infused into the ceramic so it never fades.
Full cases: Hublot Big Bang Unico Magic Gold and ceramic variants; Omega Dark Side of the Moon (full black ceramic); Audemars Piguet Royal Oak Concept ceramic. Case-only ceramic adds 30-50% to retail vs steel equivalent due to manufacturing complexity. Case-back inlays: small ceramic inserts on tool-watch case-backs for shock or scratch resistance.
Why brands use it
Aesthetic permanence: ceramic doesn't fade, scratch, or develop patina over decades. A Cerachrom Submariner from 2010 looks identical to a new one. Colour stability: red, blue, green, brown ceramics hold their colour where painted aluminium bezels (Submariner pre-2007) faded to grey or pink. Modern luxury signalling: ceramic is recognisable as a 2000s+ luxury material; it differentiates a current-era watch from a vintage one. The brittleness limits use to non-impact-loaded surfaces (so case-back is fine, crown is not).