Greubel Forsey's $1.7m watch is made from transparent sapphire

Transparency isn't just a buzzword in politics: for a few years now, it's been a genuine trend in the world of luxury watches. For example, earlier this year, Hublot introduced its Big Bang Unico Sapphire timepiece cut straight from the sapphire – the first time the material had ever been cut on this scale.

And now from Greubel Forsey, maker of what are some of the most super-complicated timepieces in the world, comes the the Double Tourbillon 30° Technique. It's a watch the company has made for a while, but now it's offered in – you guessed it – an all-sapphire case.

Clear winner

Greubel Forsey calls it the "pinnacle of transparency," and it's easy to see why. No metal is used at all in the creation of the dial and case (save for the winding pin), allowing for a panoptic view of as much of the movement architecture – and its dynamic interactions – as possible.

Cut from a single large sapphire crystal, including the rounded, multi-angular case horns, the entire movement is flooded with light within its 38.4mm case, allowing a view into its multi-tiered design from all angles. This is a more complicated watch than the Hublot, and uses sapphire in more places, including the crown.

On tourbillon

Its actual 396-part movement may not be new – the patented tourbillon movement was first unveiled in platinum-but now its prowess is on full display. The hand-wound caliber, with 120-hour power reserve, packs two tourbillon escapements, one inside the other.

Two tourbillons that rotate at different speeds are showcased here: an outer tourbillon rotates every four minutes while an inner tourbillon, every 60 seconds. All of this has helped the movement achieve a never-before-seen 915 out of a possible 1000 points at the International Chronometry Competition.

In an edition of eight pieces to be individually created by hand over the course of the next three years, the watch is priced at US$1.275 million ($1.71m).