A watch case made entirely out of sapphire crystal is one of the top achievements in high watchmaking. The Bugatti Chiron Blue Sapphire Crystal is the result of several months of computer-aided design and manufacturing processes and traditional hand polishing. It's a challenging, multi-faceted endeavor that takes several months to complete.
For example, the tonneau-shaped Chiron case isn't a singular exterior but a mix of geometric surfaces. Then there's the hardness of sapphire. It measures 9 on the Mohs scale of hardness. Very few materials are harder, including diamond, which measures a 10. Because of this, diamond cutting and polishing tools are used to craft the case. This is both costly and time consuming, but it's absolutely necessary to produce a case with the exact dimensions and transparency that the Chiron exhibits.
Adding color to the sapphire crystal complicates the manufacturing process. The sapphire crystal begins as a powder. This is when the color is created by combining to the powder a proprietary mix of rare earth elements (a set of 17 metallic elements that are difficult to mine and process), raw minerals and metals in a process called "doping." In order to a achieve a proper deep rich color, more of these minerals, elements and metals are added.
Then this powder is heated under extreme temperatures and grows to one very large round piece of raw sapphire, about the size and shape of a coffee can. This can take anywhere from three to 15 days. Adding the color, changes the chemistry of the sapphire and increases the chances that there will be inclusions in the piece, which will make it impossible to use. Then they will have to start again.
A slice is cut out of this large piece of colored sapphire that will become the case of the Bugatti Chiron. The piece is machined and hand-polished. Because the color affects the sapphire's chemical compensation, machining and hand-polishing must be conducted in a slower and more delicate manner. Again, adding to the time it takes to complete the process. Because of this added time and difficulty, producing colored sapphire is more expensive than clear sapphire.
The most challenging aspect is the hand polishing. It's the final task of the long and complex process. This same delicate technique is used for the caseback, the top, the three crowns and other pieces that are attached to the case. A single craftsman took about of 120 hours to complete the case. Every shape of every piece has a different polishing process. The different angles of the exteriors and interiors of the case required a delicate and steady hand. But the quality, including the transparency, must be consistent throughout.
The result is a fully transparent highly stylized case that exposes every part of the 578 hand-decorated and hand-assembled components of the JCAM37 manual wound caliber. This includes the groundbreaking fully functional replica of the Bugatti W16 engine with its pistons pumping, turbochargers spinning as well as the whirl of the flying one-minute tourbillon.