A watch case made entirely out of sapphire crystal is one of the top achievements in high watchmaking. The Bugatti Chiron Tourbillon 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.
The sapphire crystal begins as a powder, heated under extreme temperatures which grows to one very large round piece of raw sapphire, about the size and shape of a coffee can. This operation can take anywhere from three to fifteen days. A slice is cut out of this large piece of sapphire that will become the case of the Bugatti Chiron. The piece is machined and hand-polished. Because of the sapphire's hardness, machining and hand-polishing must be conducted in a delicate manner. Again, adding to the time it takes to complete the process.
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 takes 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.