The Williamson Pink Star

The mine a Canadian geologist built

The stone takes its name from the Williamson mine in northern Tanzania, about 23 kilometers northeast of Shinyanga. John Thoburn Williamson, a Canadian geologist born in Montfort, Quebec, in 1907, found the kimberlite pipe there in March 1940 after years of prospecting from a base at the small Mabuki mine. He named the site Mwadui after a local chief. A local lawyer, Iqbal Chopra, helped fund him and became his partner.

Short of equipment and capital during World War II, Williamson nonetheless built the first significant diamond mine outside South Africa. By 1952 it was handling 10,000 tons a day. He owned all of its output, which made him one of the richest men in the world, and he managed it closely until he died of cancer in 1958 at 50. He never married. His three siblings sold the mine for about £4 million to a partnership of De Beers and the colonial government of Tanganyika.

Tanzania nationalized the mine in 1971. De Beers bought back 75 percent in 1994, and in February 2009 Petra Diamonds completed its purchase of that share. In 2022 it was described as one of the oldest operating diamond mines in the world, known for a lively 'bubblegum' pink.

A queen's brooch and a namesake

The mine's most famous stone came out of the ground in October 1947, a few months after Princess Elizabeth's engagement was announced. It was a 54.5-carat pink rough, and Williamson, a royalist, gave it to her as a wedding present. It was cut in London into a 23.6-carat round brilliant. Accounts differ on who cut it: one names the London firm Briefel and Lemer, and another credits Cartier.

Cartier set the stone at the center of a platinum brooch shaped like a jonquil, designed by Frederick Mew. Williamson supplied the white diamonds, 170 small brilliants, 12 baguettes and 21 marquises. His partner Chopra presented the brooch to the Queen on June 22, 1953, about three weeks after her coronation.

The 2022 stone was named for that brooch and for the CTF Pink Star, the 59.60-carat diamond that holds the auction record for any jewel. It came to market a month after Queen Elizabeth II died at Balmoral on September 8, 2022.

From 32 carats to 11

Diacore, a manufacturer that specializes in rare fancy-colored diamonds, bought the 32.32-carat rough in late 2021 for $13.8 million. The rough was Type IIa, a rare class of diamond with little or no nitrogen that includes some of the most chemically pure stones.

Cutting a colored diamond means balancing weight, clarity and color: lose too much rough and the value goes with it, but keep too much weight and the color can weaken. Diacore's cutters produced a cushion-shaped stone of 11.15 carats with Internally Flawless clarity and Fancy Vivid Pink color. Diacore had also turned the CTF Pink Star's rough into its finished stone.

GIA described the result as 'among the rarest of all gemstones,' noting that a Fancy Vivid grade in a pink diamond this size 'requires a very strong inherent bodycolor in the rough crystal,' and that the Internally Flawless clarity made the combination special. The stone was offered on an 18-karat gold ring between trapeze-cut diamonds.

Why pink is so scarce

Fewer than 3 percent of the diamonds submitted to GIA are classified as colored diamonds, and fewer than 5 percent of those are mainly pink. Most pinks fall in the faint to fancy range. In a 2018 sample of 1,000 pink diamonds GIA graded between 2008 and 2016, 83 percent weighed less than one carat.

Scientists still do not fully understand what makes a diamond pink. Yellow diamonds owe their color to nitrogen and blue diamonds to boron, but no trace element explains pink. Manganese was once suspected and has been ruled out. The leading explanation is distortion in the crystal lattice from pressure and heat deep underground, which changes how the stone absorbs green light.

The supply has also shrunk. The Argyle mine in Australia, which produced more than 90 percent of the world's pink diamonds, closed in November 2020 after its gem-quality supply ran out. The Williamson Pink Star is only the second Internally Flawless Fancy Vivid pink over 10 carats ever offered at auction. The first was the CTF Pink Star.

Twenty minutes in Hong Kong

The stone was unveiled in London on August 31, 2022, and toured Dubai, Singapore, Taipei and Hong Kong. It was estimated at about HK$170 million, or $21 million. The first announcement set the single-lot sale for October 5, but it was held on the evening of October 7 at the Hong Kong Convention and Exhibition Centre, between two modern and contemporary art sales.

The bidding lasted about 20 minutes and drew nearly 50 bids. Reports disagree on the opening bid: the sale announcement said HK$130 million, while two reports written from the live stream said HK$140 million. By HK$200 million, three bidders were left, one in the room and two on the phone. They raised in steps of HK$5 million to HK$300 million, the room applauded, and the bidding went on. The hammer fell at HK$392 million, about $50 million. With fees the price was HK$453,223,000, or $57,736,078.

The sale announcement said the stone sold to an overseas representative in the room and described the buyer as a private collector based in the US. A trade report said the winning bid came by phone from a collector in Boca Raton, Florida, and that the buyer renamed it 'The Rosenberg Williamson Pink Star.' The buyer has not been publicly named.

Five million dollars a carat

At $5,178,124 per carat, the Williamson Pink Star set a world auction record per carat for any diamond or gemstone. It beat the Blue Moon of Josephine's 2015 record of $4,028,941 per carat and nearly doubled the previous pink record of $2,656,909 per carat, set by the Winston Pink Legacy in 2018.

By total price it is the second most valuable jewel or gemstone ever sold at auction, behind only the CTF Pink Star at $71.2 million. The final price was more than two and a half times the $21 million estimate.

It sold for about four times the $13.8 million Diacore had paid for the rough less than a year earlier.

The numbers

Carat weight

11.15 carats (from a 32.32-carat rough)

Color / clarity

Fancy Vivid Pink / Internally Flawless; Type IIa

Origin mine

Williamson (Mwadui) mine, Tanzania

Cutter

Diacore

Cut

Cushion shape

Price per carat

$5,178,124

Timeline

1. 1907

   John Thoburn Williamson is born in Montfort, Quebec.

2. Mar 1940

   Williamson discovers the Mwadui kimberlite pipe in what is now Tanzania.

3. Oct 1947

   A 54.5-carat pink rough is found at the mine. Williamson gives it to Princess Elizabeth as a wedding present.

4. Jun 22, 1953

   The 23.6-carat Williamson pink, set in a Cartier jonquil brooch, is presented to Queen Elizabeth II.

5. 1958

   Williamson dies of cancer at 50. His siblings sell the mine to De Beers and the government of Tanganyika for about £4 million.

6. 1971

   Tanzania nationalizes the Williamson mine.

7. 1994

   De Beers buys 75 percent of the mine.

8. Feb 2009

   Petra Diamonds completes its purchase of the mine from De Beers.

9. Nov 3, 2020

   Australia's Argyle mine, the main source of the world's pink diamonds, stops operating.

10. 2021

    Diacore buys the 32.32-carat Type IIa rough from the Williamson mine for $13.8 million in late 2021.

11. Aug 31, 2022

    The cut 11.15-carat stone is unveiled in London before a tour of Dubai, Singapore, Taipei and Hong Kong.

12. Oct 7, 2022

    It sells at a single-lot auction in Hong Kong for HK$453,223,000 ($57,736,078) with fees, a world record per carat for any diamond or gemstone.

13. Oct 2022

    A trade report says the buyer has renamed it 'The Rosenberg Williamson Pink Star.'

The world in 2022

• Sep 6, 2022

  Liz Truss becomes Prime Minister of the United Kingdom.

• Sep 8, 2022

  Queen Elizabeth II, owner of the Williamson pink brooch, dies at Balmoral Castle at 96. Charles III succeeds her.

• Sep 19, 2022

  The Queen's state funeral is held at Westminster Abbey.

• Sep 27, 2022

  Hurricane Ian strikes Cuba and the United States, leaving the whole of Cuba without power.

• Oct 5, 2022

  OPEC+ announces a production cut of up to 2 million barrels a day.

• Oct 20, 2022

  Liz Truss announces her resignation after 45 days in office. Rishi Sunak succeeds her on October 25.

• Nov 16, 2022

  NASA launches Artemis 1, the first flight of its Space Launch System, on an uncrewed trip around the Moon.

Price record

A realized auction price is what a buyer actually paid on the date shown, including the buyer's premium where the sale reported it. It is the strongest kind of reference price, and it is a record of one sale of one object on one day, not a promise of what the next example will bring.

By reference price, The Williamson Pink Star is number 2 of 100 in the jewelry entries of the FLOAT 100. 44 of those 100 rest on a realized sale; the rest carry an asking price or a guide value, and each page says which. Rank within the FLOAT 100 itself (4 here) is editorial: how much an object defines its field, not price alone.

Did you know

• Its name honors two other diamonds: the Queen's Williamson pink and the CTF Pink Star.
• The same company cut both the Williamson Pink Star and the CTF Pink Star, the two most valuable diamonds ever sold at auction.
• John Williamson has been called the only man in the 20th century to create his own diamond mine. One visitor described him as 'an almost total recluse' whose one hobby was collecting first editions.
• It went on sale one month after the death of Queen Elizabeth II, owner of the most famous diamond from the same mine.
• It was offered between two modern and contemporary art sales because the sale's organizers compared it to a great work of art.
• No one has fully explained why pink diamonds are pink. Manganese was once suspected and has been ruled out.
• In a GIA sample of 1,000 pink diamonds, 83 percent weighed under one carat. This stone weighs 11.15.