The ‘100-Carat Man’ on Selling the World’s Rarest Diamonds

“100 carats has always been a mythical number,” says David Bennett, Worldwide Chairman of Sotheby’s International Jewellery Division. Few possess a deeper understanding of the ultra-exclusive 100-carat diamond market than Bennett, who has handled nearly 1,000 carats worth of them over his four-decade career at Sotheby’s. “I didn’t know I loved them until I started selling them,” he admits. Before joining Sotheby’s as a trainee in 1974, he had no prior experience with jewellery.

“From my first 100-carat diamond sale in 1990, I developed a passion for seeking out and presenting these exceptionally rare gemstones,” he recalls. This December, during Sotheby’s inaugural A Life of Luxury week in New York, another breathtaking 110-carat brilliant-cut diamond will take center stage. Ahead of the Magnificent Jewels auction, Sotheby’s sat down with Bennett to discuss this remarkable stone and his well-earned moniker, the '100-Carat Man.'

When did you sell your first 100-carat diamond and how did you earn your nickname?

Simply because I was the first to sell them at auction. Before 1990, a 100-carat D Flawless diamond had never appeared at auction. When I took over jewellery sales in Europe at Sotheby’s Geneva, a diamond cutter reached out with an extraordinary stone—a flawless, top-color, pear-shaped diamond of 100 carats. I knew such a rarity was worth the gamble. That night, I hardly slept, wondering if I had made a colossal mistake. But the diamond sold for a then-world-record price. Over the next five years, I sold two more, culminating in the sale of the Star of the Season in 1995, which held the record for nearly 15 years.

Is there a certain mine where such massive diamonds are more commonly found?

Not necessarily. Today, the largest rough diamonds are primarily mined in South Africa and Angola. Historically, the legendary Golconda mines in India produced remarkable stones. Brazil emerged as a source in 1728, followed by discoveries in Russia, Canada, and other parts of the world. Interestingly, nearly all blue diamonds originate from a single source: the Cullinan Mine in South Africa. However, large white diamonds can be found globally.

Who tends to be the purchaser? Institutions, royal families?

Almost all have been acquired by private individuals. In the 1990s, many went to buyers in the Middle East, particularly Saudi Arabia. Today, demand has become more international.

How rare are 100-carat coloured diamonds?

It’s exceptionally rare for diamonds over 100 carats to be anything other than yellow or brown. The ones that truly make headlines at auction are D color and either Flawless or Internally Flawless.

How large is a rough for a 100-carat stone?

It takes a massive crystal to produce a 100-carat stone. In general, it’s more than well over double the size of the 100 carats.

How long does it take to cut a rough diamond of this size?

It varies. Due to the differential hardness within diamonds, cutting can be a meticulous process. I recall one instance where finishing a single stone took over a year.

Why is the 110-carat diamond in the Magnificent Jewels auction in New York so special?

When I first saw it months ago, I was struck by its extraordinary quality. Only a handful of 100-carat brilliant-cut diamonds have ever been auctioned, and they are always showstoppers. Their sheer size is astonishing—if you see this 110-carat diamond in person, I guarantee it will appear even larger than you expect.

What are the most common cuts for a 100-carat diamond?

The natural shape of the crystal often dictates the cut. Because brilliant cuts require extremely precise proportions and result in significant weight loss, they are exceedingly rare in sizes over 100 carats. Most 100-carat diamonds are cut into emerald, pear, or oval shapes.

What is your favorite part about discovering and selling these diamonds?

Their rarity and breathtaking beauty. Diamonds are the hardest natural substance in the universe. Until the 17th century, they were valued more for their symbolism than their brilliance, as cutting techniques had yet to be refined. Seeing a magnificent diamond in its final form never ceases to amaze me.

How often do newly mined 100-carat diamonds appear at auction?

I do know a few, but the timing of when they will come up for auction is another question. When they discover a very large rough, generally you hear about it in the press because obviously the mine is very proud of it. It’s not impossible, it’s just a very auspicious event.

What are some of the most memorable jewels you have sold?

I have the world record for a ruby, known as The Sunrise Ruby. When the client showed it to me, I looked at it for twenty minutes before saying anything. I’m reminded of the Donnersmarck tiara, an unbelievable jewel that was literally breathtaking. It had emeralds, which were very likely from a 17th-century Maharaja necklace and were perhaps in the collection of Empress Eugénie. Then there’s the Blue Moon of Josephine, which from the second I saw it, I thought, I’ll have that. It’s such a winner – the shape of the stone was sensational, flawless, vivid blue, top colour. There was a wonderful diamond I sold in 2012 called the Beau Sancy. It has been in four royal families of Europe and bought by Henry IV of France for Marie de Medici. She wore it in the centre of her coronation crown. It is probably the most romantic and magical stone I’ve ever sold.

Sotheby's 100 Carat Diamonds

Sotheby’s made history in 1990 by selling its first 100-carat diamond—the Mouawad Splendour, a 101.84-carat, D color, Internally Flawless pear-shaped diamond—for nearly 16 million CHF in Geneva. Three years later, the Star of Happiness, a 100.36-carat, D color, Internally Flawless modified rectangular brilliant-cut diamond, sold for 17.8 million CHF (US$118,397 per carat). In 1995, Sotheby’s auctioned the Star of the Season, a 101.10-carat, D color, Internally Flawless pear-shaped diamond, which achieved US$16.4 million (US$164,223 per carat), setting a price-per-carat record that stood for nearly 15 years.

The allure of the 100-carat mark remains unparalleled, making every auction of such a diamond a landmark event. The appearance of a 100-carat D Flawless diamond is always newsworthy. Over the decades, only a handful of D Flawless or Internally Flawless 100-carat diamonds have surfaced at auction. In fact, less than 0.5% of all diamonds over one carat submitted annually to the GIA achieve the coveted D, Internally Flawless, or D, Flawless grades.

As the market leader in selling the world's largest and finest diamonds, Sotheby’s continues to set the standard for excellence in the realm of high jewellery.

Advantages to Buying Diamonds on the Secondary Market

1. Access

Sotheby’s provides exclusive access to a curated selection of diamond jewelry  from the world’s most prestigious Maison's, including Van Cleef & Arpels, Cartier, Tiffany & Co and more. Clients can find top quality diamonds from one carat to more than twenty carats from top brands and bespoke creations. Our jewelry specialists work closely with collectors worldwide to source coveted diamond jewelry to provide exclusive access to the rarest and most desirable diamond jewelry.

2. Flexibility

Sotheby’s offers unique access to a wide selection of signed and unsigned diamond jewelry available at auction around the world. We also offer diamond jewelry for immediate purchase and allow easy side-by-side comparison of top brands and unsigned diamonds. We also offer a bespoke concierge service to help source unique one-of-a-kind diamond jewelry.

3. Value

The secondary market is an attractive alternative for purchasing diamond jewelry since you can realize more value compared to traditional retailers. Top brands and jewelry retailers add a material premium to cover manufacturing and other fixed costs that are not reflected in the prices at Sotheby’s. It’s possible to purchase classic diamond jewelry from top brands including Tiffany & Co., Cartier and Harry Winston at less than half of the original retail price. These pieces also often include the original packaging and certificates. Sotheby’s Jewelry specialists also inspect every item before accepting it for sale.

4. Discovery

One of the greatest advantages of shopping in a global luxury marketplace is the opportunity to discover rare and unique diamond jewelry pieces that are no longer available through traditional retail channels. Our curated selection of diamond jewelry is continuously refreshed, ensuring that you’ll always find something new and exclusive to build your collection.

Buy and Sell Diamond Jewelry At Sotheby's

Sotheby's often has impressive diamond jewelry available at auction. Sotheby's also has a curated selection of diamond jewelry available for immediate purchase on marketplace. If you would like to view diamond jewelry, a salon specialist would be happy to assist. Sotheby's is also able to source an exceptional diamond jewelry creation from its global supplier network.

Explore upcoming jewelry at auctions in New York, London, Switzerland, Paris, and Hong Kong.
Contact a Salon Associate in New York or Hong Kong to schedule an appointment.
Speak to a Jewelry Specialist about selling diamond jewelry.

Trust our worldwide network of leading jewelry specialists from a globally renowned auction house established in 1744.