Sapphire is known as a particularly scratch-resistant material and one of the hardest materials on Earth, with a Mohs rating of 9.0. Made of aluminium oxide (Al2O3) crystals, it is transparent thanks to its molecular composition.
The machining of such components was the biggest challenge faced by Richard Mille, a challenge made all the more difficult as the sapphire machining process is exceptionally delicate. Although extremely tough, sapphire does not allow for even the slightest error during milling and cutting. Creating a case of this quality took over 1000 hours of machining, of which 430 hours were spent on pre-forming the case components and 350 hours on polishing the whole watch case. The cutting tools must be specially designed and tipped with diamond.
For excellent optical properties, bezel case parts have been treated with an anti-glare coating. The tripartite case is water resistant to 50 metres, ensured by two Nitrile O-ring seals. The case is assembled with 20 Spline screws in grade 5 titanium and abrasion resistant washers in 316L stainless steel.