A sapphire case is a watch case made from synthetic sapphire. Watchmakers value the material because it is clear, very hard and difficult to scratch. That same hardness makes it hard to work. Only diamond is harder, and sapphire is brittle as well, so shaping a case is slow and demanding work.
What is sapphire?
Sapphire is a form of corundum, which is aluminium oxide. Ruby is also corundum, so the two stones belong to the same mineral family. Watch cases use synthetic sapphire, which is grown in a laboratory. Lab-grown sapphire can be made in any colour, so a case does not have to be clear. Hublot appears to have been the first brand to make a watch in orange sapphire. It has probably released more sapphire-cased models than any other brand.
Why is a sapphire case so hard to make?
Diamond is the only material harder than sapphire, so cutting tools struggle to shape it. Sapphire is also brittle, which means it tends to crack or chip rather than bend. Together, these make every stage slow. Richard Mille says milling and polishing a single sapphire case takes more than a thousand hours. Each case of its RM056 was cut from one solid piece of sapphire. That took about six weeks of non-stop machining.
Where it comes from
Watchmakers began using sapphire roughly a hundred years ago, at first only for crystals, the clear covers over the dial. In 1980 the watchmaker Vincent Calabrese designed a sapphire-cased watch for Corum. The modern form of the sapphire-cased watch has been dated to 2012, when Richard Mille released the RM056. The same brand brought out its first coloured sapphire case in 2015, on the RM 07-02 Automatic Sapphire. Writing about four decades after the first sapphire-cased watch appeared, Watchonista treated it as a milestone.
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