What prevented watchmakers from using it to make cases were prohibitive high costs, the diffi culty in machining it, and the immense amount of fi nishing needed. Its unyielding nature means it requires expensive diamond-tipped milling machines to cut and sculpt, but then its brittleness makes it prone to shattering while being worked on.
Then there is the question of geometry. A flat or domed crystal is easy, but a case – even a simple round one – is infi nitely more complicated to sculpt. According to Richard Mille, its RM 056 required 1,000 hours of machining, including 430 hours of filing and 350 hours of polishing to turn the naturally opaque surface transparent. That translates to 125 days of work.
Finally, there is the issue of, well, transparency. With a fully transparent case, everything is on show, so the movement needs to be well constructed and fi nished.
But the watchmaking industry loves nothing more than a challenge, because surmounting that challenge gives bragging rights. So despite all these obstacles, more and more companies are jumping on the sapphire bandwagon. We bring you a clear look at the latest pieces.