Richard Mille was a pioneering force in this area of horological design, while MB&F, Greubel Forsey and Hublot are increasingly pushing the boundaries of form and cutting technology. Not only does the use of sapphire crystal result in a visually arresting watch housing, but its toughness is almost unrivalled. ‘It can only be marked by a diamond, so it stays beautifully transparent, without any scratches,’ says Ricardo Guadalupe, Hublot’s CEO.
Synthetic sapphire, the base material, is grown in laboratories using a melted mixture of aluminium oxide that, on cooling, forms crystal cylinders known as ‘boules’. Its scratch resistance makes it popular as a ‘glass’ in industrial design; it is used in barcode scanners, laser rods and new-generation iPhones to protect the camera lens. Watch cases, however, are an entirely different affair, demanding more complicated shapes, water resistance and a fine finish.
Sapphire crystal’s extreme hardness is countered by a susceptibility to chipping, cracking or shattering. ‘The manufacturing process is long and complicated,’ Guadalupe says. ‘There can be a lot of breakage, and we need to restart the process many times from the raw material, to have the perfect shape and colour.’
Cutting and shaping a case is a seven-step process. The raw material is cut according to the final product size. It is then ground to the general shape, followed by CNC drilling of the required holes. CNC is used again to cut different case forms. Next, sandblasting finishes the holes, followed by fine polishing and, lastly, final polishing. The time-consuming polishing stages require extremely high-quality diamond powders.
For Hublot’s ‘Big Bang Unico Magic Sapphire’ chronograph, it sought the expertise of a Swiss sapphire crystal specialist, who collaborated with its horological engineers. The titanium screws and crown complement the look. Water-resistant to approximately 100m, with a power reserve of around 72 hours, this limited-edition timepiece has a production run of just 500.
As originally featured in the Precious Index, our new watches and jewellery supplement (see W*218)