Why Audemars Piguet’s New Jumbo Extra-Thin Has A Glass Bezel

If you have ever owned, or know anyone who has owned, a Royal Oak, one thing you’re undoubtedly aware of is the tendency for the beautifully machined and finished bezel – a design element so iconic that I am actually forced to use the word – to pick up scratches and nicks. Of course every watch case in any material can pick up scratches and nicks – there is a Patek Nautilus in the London Science Museum, which George Daniels used as a prototype for an early version of the co-axial escapement, which has a bezel so badly scratched that I thought at first that it was diamond-set when I saw it for the first time in 2018.

The finish on the Royal Oak bezel is extremely well-defined, crisp, and since 1972 has been famous for being almost jewel-like, but the downside is that even the slightest nick or scratch has nowhere to hide. A lot of watches gradually pick up a kind of wabi-sabi appeal as they accumulate signs of wear, but the Royal Oak bezel is notorious for making even the slightest ding visible and wearing one on a daily basis has, it’s always seemed to me, required a certain level of philosophical resignation (one of the first thing that  vintage AP collectors learn to look out for, are RO bezels which have had their geometry spoiled by over-enthusiastic polishing).

Which is why one of the latest versions of the beloved Jumbo, which was updated for the 50th anniversary of the Royal Oak with the new caliber 7121 (without adding anything to the thickness) has a bezel and caseback made of a material with a somewhat misleading name: bulk metallic glass, or BMG.

Heart Of Glass, Harder Than Stone

Bulk metallic glass has a confusing name, although misleading people was not the intention of its inventors. Most metal alloys – let’s go out on a limb and say, virtually all standard metal alloys – have a crystal structure consisting of repeating geometric units, and it is the size, orientation, and strength of atomic and intermolecular bonds that determines the properties of the alloy in question. The size of the crystals is determined by several factors but one of the most important is the rate at which the alloy cools.

Rapid cooling tends to produce smaller crystals – controlling different cooling rates is critical in giving the katana, or Japanese sword, its complex metallurgic properties, which inspired a recent release from Grand Seiko. Slower cooling produces larger crystals, and one of the most amazing examples of very slow, very large crystal growth in watchmaking, are the enormous iron crystals formed in slowly cooling iron-nickel asteroids, which take millions of years to form and which are responsible for the Widmanstätten patterns seen on meteor watch dials (although there are other types of meteorites that can be used for watch dials as well).

If you cool an alloy fast enough, crystals don’t have any time to form at all, and what you end up with is technically a glass, which has an amorphous internal structure and is generally quite hard, although silica glass (the kind in your windows) is also brittle and has a tendency to shatter. However, metallic glasses can be extremely hard and much more scratch resistant than conventional watch case alloys. In recent years, several makers have experimented with BMG as a case material (it has many other applications as well) and for Only Watch 2021, Audemars Piguet submitted the last classic 15202 Jumbo with the caliber 2121, in a case with a BMG bezel and caseback. That watch ended up selling for CHF 3.1 million.

As counterintuitive as a metallic glass sounds, they are in fact classified as a type of glass, thanks to their internal crystal structure (or I guess I should say, their lack of  a regular internal crystal structure).

AP Jumbo for Only Watch 2021.

The big advantage in using BMG for the Royal Oak Jumbo – really, it’d be ideal for any Royal Oak or Royal Oak Offshore, thanks to its technical properties – is its high level of scratch resistance. AP hasn’t released an HV (Vickers hardness number) for the BMG elements in the new reference 16202XT.OO.1240XT.01 but some digging around reveals that palladium BMG, which is what AP has used here is as you might expect, pretty tough stuff. In fact, the good folks at the Johnson Matthey Technical Review, back in 2021, in a review of BMG for jewelry and watch cases, singled out palladium BMG for its notably superior performance, saying in part, “The remarkable properties of platinum-based and palladium-based BMGs and the particularly high GFA of palladium-based compositions … means they have been the subject of substantial research. While being initially developed for scratch-resistant, hallmark-compliant jewelry, it was found that some platinum-based BMGs show a record-breaking combination of excellent strength and toughness.”

Modern Watchmaking Problems, Modern Watchmaking Solutions

Audemars Piguet has, I think partly in response to stubborn nostalgists like myself who just won’t stop mourning the caliber 2121 which powered the original Jumbo, been at some pains this time around to tout the advantages of the new caliber 7121.

To quote AP on the subject, “Having taken five years to develop, Calibre 7121 produces more energy than its predecessor thanks to its new construction and larger barrel. This gain enables the mechanism to achieve greater precision over a longer period of time. The central oscillating weight is mounted on ball bearings and is equipped with two reversers1 that ensure bidirectional winding. The balance wheel is fitted with weights that are embedded into the thickness to avoid any aerodynamic friction which would slow down the movement. Calibre 7121 is also equipped with a patented date mechanism that is both extremely thin and energy efficient.”

Now I’m never going to stop wishing that the 2121 were still in the Jumbo but the truth is, as fine a piece of work as it was and is (today it is only available in a small handful of watches from AP and Vacheron and then only as the base movement for complications) it has been around since 1967 and there are perishingly few movements from that period which are still in service in an unmodified form. Expensive to produce, challenging to service and yes, lacking a quickset date, the 2121 certainly has history and sheer excellence of horological beauty and craft on its side, but that alone does not a modern movement make.

Still, the whole issue reminds me of the beginning of Butch Cassidy And The Sundance Kid, during which Butch watches a bank close for the night with an enormous number of locks, bars, and other barriers. On his way out, he asks a guard, “What happened to the old bank? It was beautiful!” The guard replies, in a stern monotone, “People kept robbing it.” To which Butch replies, “That’s a small price to pay for beauty.”

And the new reference is a gorgeous watch. AP has produced some very attractive fumé dials for the 50th anniversary of the Royal Oak (including the 16202BA.OO.1240BA.01 in yellow gold, which combines the classic tapisserie pattern with a beautiful yellow-black gradient) and the new red gradient dial on this new model is easily as charming as anything that came out for the birthday party in 2022. It’ll be interesting to see what further use AP might make of BMG’s technical properties – the stuff is challenging to work with for a number of reasons, including the rapid cooling time needed, but its structural and material features would seem to make it a perfect materials choice to protect the admirable geometry of one of watchmaking’s great classic designs.

The Royal Oak Jumbo in BMG and titanium: case, titanium with BMG bezel and caseback surround, AR coated sapphire front and back, 39mm x 81.mm, water resistance, 50 meters. Smoked burgundy dial with sunburst motif, 18k pink gold hour markers and hands. Bracelet in satin finished titanium with BMG studs and titanium folding clasp. Movement, caliber 7121, 29.6mm x 3.2mm, 55 hour power reserve, running in 33 jewels at 28,800 vph.