This is Oystersteel, a high-performance steel of grade 904L produced for Rolex.
A stainless alloy which, once polished, will retain its brilliance and beauty in all circumstances. Rich in chromium and molybdenum and extremely resistant to impact and corrosion, Rolex inspects Oystersteel on a microscopic scale – from the shaping throughout the priming processes – to control and refine its microstructure prior to machining and final polishing.
But its greatest test is not in Rolex's inspecting or polishing: the true challenge is found out in the world, in everyday life as much as nature’s most extreme conditions.