The word "carat", when referring to the weight of a diamond, comes from the Greek word keration, or carob bean, a unit that has been used to measure precious stones since the 16th century.
One carat equals one bean, roughly, and while many an aspiring bride today knows exactly what a one-carat diamond might look like on her finger, few of us are familiar with the dimensions of a single carob bean, let alone 163.41 of them. (I tracked one down, and it’s about the size of a petit pois.)

A whopping 163.41ct – that’s the official size of the gigantic emerald-cut stone anchoring a new necklace by Swiss jewellery house de Grisogono as the brand celebrates its 25th anniversary. Fittingly flamboyant, the necklace itself is a huge, swooping collar of emeralds and diamonds, with the main event on a detachable setting at its base. And while the diamond is by far the largest the brand has had the privilege of working with, the necklace is typically "de Gris" (as it’s affectionately known by its jet-set clients), bold in colour and scale and high on glamour.

The whole thing is named "the Art of de Grisogono – Beyond Jewellery, Creation 1", and while that’s quite the name for a necklace, it’s also quite a piece, and it is set to be auctioned at the Magnificent Jewels sale at Christie’s, Geneva, on 13 November. The finished product will have taken nearly two years to get to that point: the 404ct rough diamond it started as was discovered in an Angolan mine in early 2016.
The 404ct rough diamond was discovered in an Angolan mine

But how big is an emerald-cut 163.41ct diamond, carob seeds aside? How many of them would it take to fill a matchbox, or squeeze into a Tic Tac packet? Could you swallow it whole or would you need to chop it up first? I, like most, have only the vaguest idea, so I ask Fawaz Gruosi, founder and creative director of de Grisogono, to put it into words.

"It’s quite difficult to compare it to anything else," Gruosi tells says. "To compare it to an object won’t convey the true feeling I got while holding it. It is extremely soft to touch, quite heavy, and fits perfectly into the palm. A talisman that you wish to keep in your hand forever." Gianluca Maina, de Grisogono’s globetrotting marketing director, is far more upfront. "It’s domino-sized," he says, matter-of-factly, which is a description most of us can get our heads around.
Fawaz Gruosi, founder of De Grisogono, holding the rough diamond CREDIT: TOBY GLANVILLE

To say that the de Grisogono team is intimately acquainted with the stone is no exaggeration, for this rock’s journey from rough stone to the big Swiss sale has been a carefully managed process involving three main players: de Grisogono, the jeweller who created the necklace; Nemesis, the diamond trader that first acquired the uncut stone; and Christie’s, the auction house bringing the finished product to the market.

"We hope to sell one major piece a year with Christie’s; they will be a series of jewels dedicated to the incredible creations of de Grisogono, featuring equally important roughs," Maina explains.

This three-pronged, public approach to selling a very large stone (the 27th-largest diamond ever found) isn’t the usual one. When big gemstones go to auction, they’re either old, famous rocks that have passed through many hands, or new stones marketed by the auction house with little mention of the other players. All anyone generally cares about is who buys it, and for what price. But what goes on in the lead-up is just as fascinating.
The Art of de Grisogono - Beyond Jewellery, Creation 1 CREDIT: TOBY GLANVILLE

Moshe Klein, whose family company was responsible for cutting and polishing the diamond in June last year, after the initial "cleaving" of the 404ct rough. This is the point at which the diamond is first split across one of its planes, and it’s a pretty primitive-sounding process compared with all the precautions taken beforehand.

"The rough stone goes back and forth between a lot of experienced people in various parts of the world for analysis before we even make that first cut," Klein explains. "We use a Galaxy laser to examine the stone before we cleave it, which is probably the newest technology in the world, but we use the oldest technology to actually make the cut: a little scratch is made in the stone with a small piece of rough, then we put in a special knife and split it."
The rough diamond was the 27th largest ever found

Klein describes the moment of cleaving as an intense one. "I missed a couple of heartbeats," he admits. "Mr Gruosi was watching, too, and at the moment it was cleaved we were holding hands and holding our breath. God forbid it could have cleaved off a chunk of the main part of the stone we were hoping to preserve."

The goal, as with all precious gems, was to get the largest polished stone of the highest quality out of the rough. In this case, the 404ct rough yielded more than everyone’s wildest dreams: a 163.41ct, Type IIa (as close to chemically pure as a diamond can get), D-Flawless (as colourless and unsullied as they come) stone with serious value.

"We won’t know what the piece is worth until we sell it," says Rahul Kadakia, head of the jewellery department at Christie’s New York, who is responsible for not only the key auction but also for the marketing of the necklace in the run-up to it. "There is no estimate, because it depends on what the buyer is willing to pay," Kadakia, ever the salesman, explains. "But it would be at least $30 million for the diamond, and another $3 million for the necklace."
Fawaz Gruosi CREDIT: TOBY GLANVILLE

Meanwhile, after its grand unveiling, in Hong Kong in September, the necklace is accompanying Kadakia on a world tour for prospective clients in Qatar, Dubai, London and New York. "It’s the largest diamond of its kind in the world, so there’s going to be a lot of interest," he says. "Not just from members of the trade but also from clients who want to buy it as an investment. There are maybe eight or so who could afford to do so. It really catapults de Grisogono into another category, offering a diamond of this cut and quality larger than anyone has ever seen."

As for Gruosi, 13 November will be quite a day. "I’ve been a jeweller for almost 30 years," he says. "Yet I never thought it would be possible to be involved with such an exceptional stone, and from the very beginning. The diamond we ended up with is so extraordinary, it is like a dream. I can hardly believe it."


As for the auction itself, will he be there? "Of course!" he says. "But  I think I might die when the gavel comes down."

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