Transparency is something that fascinates humankind, especially when it’s used in design.

And what better way is there to reveal the inner workings of something than to remove the covers and reveal its very soul?

This idea was probably first successfully implemented in a wristwatch in a serial sense by Corum with its Golden Bridge in 1980. Corum, which can surely be termed the father of wearable transparency, was spurred on in exploring this route by the belief of co-founder René Bannwart and independent watchmaker Vincent Calabrese that the work of the watchmaker should not be hidden from view.

In 2009, MB&F revived the transparency idea by introducing the rectangular HM2 SV, the top half of which was crafted in transparent sapphire, completely revealing the top of the movement.

MB&F HM2 SV of 2009

Richard Mille went even further at the 2012 SIHH with the introduction of the million-dollar five-piece limited edition RM 056 Felipe Massa Sapphire, whose fully transparent case revealing oodles of complicated gearing coming together to make a split-seconds chronograph movement with 70 hours of power reserve, a torque indicator, and a function indicator was nothing short of mesmerizing.

Richard Mille RM 056 Felipe Massa Sapphire from 2012

The production of the RM 056’s sapphire crystal case took years of research and testing. When that was through, the three-part case by itself needed more than 1,000 hours of machining: 430 hours for pre-forming the sapphire crystal components and another 350 hours just for the polishing.

But it was completely worth it – the effect is stunning. And the brand continues to delight its avid collectors with variations on the theme, like the recently released RM 07-02 Pink Lady Sapphire.

Richard Mille RM 07-02 Pink Lady Sapphire

I would not like to call this a new trend, but since Richard Mille’s RM 056, other brands have done their own research into the area to come up with some awe-inspiring transparency.

At Baselworld 2016, we found five – in fact, six – examples of the ultimate in sapphire crystal transparency.

4N Sapphire Planet

“I wanted to create a new case in sapphire crystal to set in majesty the movement with its exceptional three-dimensional architecture,” François Quentin, founder and designer of 4N, explained at Baselworld. “The idea was to highlight the mechanism and offer a setting that allows the observer to plunge into the heart of the mechanism. Transparency was the key to this new project.”

4N Sapphire Planet

Mission accomplished. The sapphire crystal case, which was manufactured in one piece – certainly a massive technical challenge as evidenced by the two years it took to complete – allows us to admire the highly complicated manually wound movement comprising 514 components that Quentin created in conjunction with Audemars Piguet Renaud et Papi.

This complicated jump hour (and minute) watch boasts a complex system of three turntables displaying the minutes and hours digitally. The end effect is a beautiful dance on the dial side.

4N Sapphire Planet from the side

See A Watch Nerd’s 7 Favorite Digital Watches for more on this timepiece in its original form and other cool “digital” timepieces.

Quick Facts 4N Sapphire Planet
Case: 37 x 52 x 16 mm, sapphire crystal
Movement: manually wound Caliber MVT01/D01 with 237-hour power reserve via twin spring barrels
Functions: digital display of hours and minutes via three carousels and ten numbered discs
Limitation: 3 pieces, each customizable to an extent by the owner
Price: €280,000

Rebellion  540 Magnum Sapphire Tourbillon

Rebellion’s 540 Magnum Sapphire Tourbillon, whose modular case comprising eight separate elements needed 47,600 minutes of polishing is, to date, the world’s most complex sapphire crystal case. These 47,600 minutes do not include the time devoted to researching and developing the concept, and programming the advanced 3D software needed to research, design, and develop.

Rebellion 540 Magnum Sapphire Tourbillon

Those 47,600 minutes were needed to shape, grind, and polish the sapphire crystal components and that’s all.

To put that in perspective, 47,600 minutes is equal to 99 business days (20 weeks): that’s nearly half a year.

Rebellion 540 Magnum Sapphire Tourbillon

This incredible timepiece has equally incredible pedigree: it was conceived by designer Eric Giroud and watchmaker David Candaux.

“We had to put a lot of thought into finding ways to avoid changing the aesthetics of the watch while managing to assemble all the elements and making sure all the connecting elements were invisible,” says Candaux.

For more information, please visit www.rebellion-timepieces.com/magnum-540-grand-tourbillon.

Quick Facts Rebellion 540 Magnum Tourbillon
Case: 46 x 56.7 x 19.6 mm, sapphire crystal with transparent silicon gasket
Movement: manually wound Caliber REB T-14 with twin spring barrels for 14-day power reserve; one-minute tourbillon; magnesium-caged tourbillon diameter 17.2 mm
Functions: hours, minutes; power reserve indicator expressed in days
Price: 1.8 million Swiss francs

Hublot Big Bang Unico Sapphire and Big Bang Unico Black Magic

I seriously do not understand how Hublot has managed to not only offer 500 pieces of the Big Bang Unico Sapphire in what the brand calls “viable sapphire crystal,” but to offer it at the price it does: at $57,900, it costs only a fraction of the other sapphire crystal-encased timepieces listed here.

Hublot Big Bang Unico Sapphire

Perhaps it has something to do with an exclusive partnership with a Swiss supplier that the other brands are not using. And perhaps it also has to do with the pieces of reinforcing titanium used in components such as the screws, push pieces, deployant buckle, and silicone-molded crown as well as the transparent composite resin lugs.

Hublot Big Bang Unico Sapphire

The skeletonized dial, which celebrates the movement as much as the case does, is crafted in transparent resin.

The Big Bang Unico Sapphire follows Hublot’s foray into sapphire crystal cases with the one-of-a-kind MP-05 LaFerrari Sapphire, a $600,000 timepiece introduced in January 2016.

And, amazingly, Hublot also introduced a second sapphire crystal timepiece at Baselworld, this time to celebrate the tenth anniversary of Hublot’s all-black styling.

Hublot Big Bang Unico Sapphire All Black

The Big Bang Unico Sapphire All Black reverses the natural order of sapphire crystal: instead of revealing, it makes everything invisible.

Hublot Big Bang Unico Sapphire All Black

“In the original All Black concept, the watch is visible but the time display is invisible,” says Hublot CEO Ricardo Guadalupe. “The Big Bang Unico Sapphire All Black plays with transparency; technically it is invisible but, conversely, the time display is rendered visible. It makes our proprietary Unico movement fully and completely visible.”

Decide for yourself which one you like best.

For more information, please visit www.hublot.com/big-bang-unico-sapphire-in-complete-transparency and/or www.hublot.com//big-bang-unico-sapphire-all-black.

Quick Facts Big Bang Unico Sapphire
Case: 45 mm, sapphire crystal with transparent composite resin lugs, water-resistant to 50 m
Movement: automatic Caliber Unico HUB1242 with 72-hour power reserve
Functions: hours, minutes, seconds; flyback chronograph
Limitation: 500 pieces
Price: $57,900

Quick Facts Big Bang Unico Sapphire All Black
Case: 45 mm, smoky sapphire crystal with transparent black composite resin lugs, water-resistant to 50 m
Movement: automatic Caliber Unico HUB1242 with 72-hour power reserve
Functions: hours, minutes, seconds; flyback chronograph
Limitation: 500 pieces
Price: $64,000

Bell & Ross BR-X1 Tourbillon Chronograph Sapphire

For me the BR-X1 Tourbillon Chronograph Sapphire was one of the talking pieces of Baselworld because of its unexpectedness. And the case is cut from one single block of sapphire crystal – a very expensive case indeed.

Bell & Ross BR-X1 Tourbillon Chronograph Sapphire

Aside from its transparent case shaped in Bell & Ross’ now immediately recognizable pilot’s square, my favorite detail of this timepiece is the tourbillon cage shaped as the brand’s ampersand.

Bell & Ross BR-X1 Tourbillon Chronograph Sapphire

For more information, please visit www.bellross.com/BR-X1-tourbillon-sapphire.

Quick Facts Bell & Ross BR-X1 Tourbillon Chronograph Sapphire
Case: 45 mm, sapphire crystal with titanium crown
Movement: manually wound Caliber BR-Cal.285 with one-minute flying tourbillon (MHC base) and 100-hour power reserve
Functions: hours, minutes; monopusher chronograph
Limitation: 5 pieces
Price: $500,000

MB&F HM6 SV

With HM6 SV, MB&F has added a completely new dimension to transparent sapphire crystal cases: biomorphism. The crystal-clear, apparently amorphous curves and domes on the fully transparent – top and bottom – case plates of HM6 SV bring softness to the world’s hardest mineral after diamond.

MB&F HM6 SV

You may also like It’s Transparently Brilliant! HM6 SV By MB&F.

HM6 SV by MB&F

For more information, please visit www.mbandf.com/machines/horological-machines/hm6.

Quick Facts MB&F HM6 SV
Case: 51 x 50 mm, sapphire crystal plate sandwich construction, 5N red gold/sapphire crystal or 950 platinum/sapphire crystal
Movement: automatic caliber with one-minute flying tourbillon, 2.5 Hz frequency, 72-hour power reserve
Functions: hour and minutes on separate semi-spherical aluminum indications, retractable tourbillon cover, dual turbines to regulate automatic winding speed
Limitation: 10 pieces in platinum/sapphire crystal and 10 pieces in red gold/sapphire crystal
Price: 350,000 Swiss francs (excluding taxes) in red gold and 380,000 Swiss francs (excluding taxes) in platinum