Cerachrom is a special type of ceramic used by Rolex.
Rolex was among the pioneers of ceramic watch cases and components. Their proprietary Cerachrom ceramic is designed to be highly resistant to fading in sunlight and corrosion by water. Most Cerachrom bezels include numerals and marks that are coated in gold or platinum through PVD.
Cerachrom is used in the modern Rolex GMT-Master II, Rolex Submariner, and Rolex Sea-Dweller watch bezels.