Luxury Guide to Buying an Exceptional Round Diamond Engagement Ring
What to Consider when Buying a 3-Carat or Larger Round Cut Diamond
Learn everything you need to know about buying a round diamond engagement ring.
History of Round Cut Diamonds
The first round cut diamonds can be traced back to the 17th century with the development of the "Mazarin cut," named after Cardinal Mazarin of France. This cut featured 17 facets and was a precursor to the modern round brilliant cut. The "Old Mine Cut" emerged, characterized by a squarish shape with a high crown, small table, and large culet. These early round diamonds had fewer facets and less symmetry compared to modern cuts. The "Old European Cut" was developed, which was more round in shape than the Old Mine Cut. It had a higher crown, smaller table, and more symmetrical facets. This cut was a significant step towards the modern round brilliant cut. Advances in diamond cutting technology and the use of steam-powered cutting wheels allowed for more precise and consistent cuts. This period saw the transition from Old Mine Cuts to Old European Cuts.
The modern round brilliant cut as we know it began to take shape in the early 20th century. The use of mathematical principles to optimize light performance was pioneered by Marcel Tolkowsky, a mathematician and diamond cutter. Marcel Tolkowsky published his seminal work, "Diamond Design: A Study of the Reflection and Refraction of Light in Diamond." He calculated the ideal proportions for a diamond to achieve maximum brilliance and fire. Tolkowsky's ideal cut included 58 facets: 33 on the crown (top) and 25 on the pavilion (bottom). The introduction of advanced diamond cutting machines and computer-aided design (CAD) further refined the precision and consistency of the round brilliant cut. These technologies allowed cutters to achieve Tolkowsky's ideal proportions with greater accuracy.
Continuous improvements in cutting technology, including laser cutting and 3D modeling, have enabled even finer precision and creativity in diamond cutting. The round brilliant cut remains the most popular and sought-after diamond shape, accounting for over 70% of all diamonds sold.
Popularity of Round Cut Diamonds
The round diamond is timeless and versatile, complementing various ring settings and styles. It has been the most popular diamond shape for over a century, making it a classic choice for engagement rings. The round diamond is often associated with timelessness, eternity, and unbroken commitment, which aligns with the symbolic meaning of engagement rings. This emotional resonance enhances their popularity.
Famous rounds diamonds include The Cullinan I or Great Star of Africa. It is a D flawless round diamond weighing 530.20 carats. The Cullinan I is the largest polished white diamond in the world. It was cut from the largest rough diamond ever found, the Cullinan Diamond, which weighed 3,106 carats. The Cullinan I is set in the head of the Sovereign’s Sceptre with Cross, part of the British Crown Jewels, and is displayed in the Tower of London. The Orlov Diamond is 189.62 carats and slightly blueish green. The Orlov Diamond is believed to have originated from India and is part of the Diamond Fund of the Moscow Kremlin. It is known for its rose-cut and its historical association with Catherine the Great, who received it from her lover, Count Grigory Orlov.
The 4 Cs: Carat, Clarity, Color, and Cut
Round brilliant cut diamonds are designed with 58 facets to maximize light reflection, which gives them unparalleled brilliance and fire compared to other diamond cuts.
Carat: As a luxury seller of diamonds, Sotheby's generally carries round diamonds that are 3 carats and larger. Sotheby's sells some smaller round diamonds but these are either colored diamonds or very high quality diamonds that are classified as colorless and in the flawless/internally flawless clarity grade.
Clarity: We recommend VS clarity or better for a round cut diamond.
Color: We recommend H color or better for round cut diamonds 3 carats and larger.
Cut: The modern round brilliant cut typically has 58 facets (57 if there is no culet). Key proportions include a table size of 53-58%, a depth of 59-62.5%, and specific angles for the crown and pavilion to maximize light performance. The round brilliant cut is known for its unparalleled brilliance (white light return) and fire (dispersion of colored light).
Type I and Type II Diamonds
About 95% of diamonds are Type Ia and contain trace amount of nitrogen. Most engagement rings and other diamond jewelry are made from Type Ia diamonds. Type Ib diamonds are often associated with intense canary yellow diamonds and are often used for jewelry. Type II diamonds are much rarer than Type I diamonds and have fewer inclusions and higher clarity than the more common Type I diamonds.
Type IIa diamonds are the purest form of diamonds with no measurable nitrogen or boron impurities. These diamonds are often colorless but can also be found in rare colors like pink, brown or blue. These are extremely rare and comprise less and 2% of all mined diamonds. These diamonds are formed under high-pressure and high-temperature conditions which can give the diamond higher clarity and brilliance. Sotheby's sold a Harry Winston Type IIa round diamond ring weighing 15.18 carats for just over $1 million in 2023.
Type IIb diamonds contain boron which give them blue or grayish-blue color. Unlike other diamonds, Type IIb are semiconductors and can conduct electricity and are even rarer than Type IIa diamonds. The Hope Diamond is an example of a famous Type IIb diamond.
Fancy Colored Round Cut Diamonds
While there are fancy colored round diamonds, it a less popular cut for colored diamonds. Round cuts are known for their brilliance and ability to reflect light, but this can sometimes dilute the color of a fancy colored diamond. Fancy colored diamonds are valued for their intense and pure color, so cuts that maximize color retention, like cushion, radiant, or pear shapes, are often preferred. Cutting a diamond into a round shape typically results in more material loss compared to other cuts. Since fancy colored diamonds are rare and valuable, preserving as much of the rough diamond as possible is often a priority. This makes less wasteful cuts like cushion, radiant, and oval more popular choices. While round brilliant cuts are the most popular and traditional choice for colorless diamonds due to their optimal light performance, fancy colored diamonds are often showcased in cuts that enhance their unique hues. The aesthetics of the cut and its ability to showcase the diamond’s color are major considerations.
Celebrity Round Cut Diamond Engagement Rings
Emily Blunt received a 3 carat round cut diamond engagement ring from John Krasinski in 2009. Ashton Kutcher proposed to Mila Kunis with a 5 carat round cut diamond ring set on a platinum band. Carry Underwood's engagement ring is a round cut yellow diamond estimated to be 5 carats. Ciara's engagement ring from Russell Wilson features a carat round cut diamond that is estimated to be 16 carats. Kate Upton received an 8-carat round cut diamond engagement ring from Just Verlander.
Buying a Round Cut Diamond Engagement Ring at Sotheby's
Sotheby's sells natural round cut diamond engagement rings on its marketplace, available for immediate shipping. Prices start at around $40,000 for a 3 carat round cut diamond engagement ring that is VS clarity and H color. This price can vary depending on the cut, fluorescence, polish, brand and provenance. Along with high quality unsigned diamond rings VS clarity and H color or better, Sotheby's also sells round cut diamond rings from top luxury brands including Harry Winston, Tiffany, Cartier and more. Sotheby's also sells rare and impressive round cut diamond engagement rings at auctions in New York, London, Switzerland, Paris and Hong Kong. You can also contact a Client Advisor in New York or Bucherer in Zurich to learn more about Sotheby's diamond engagement rings. In addition to the available round cut diamond rings listed on marketplace or available at auction, Sotheby's is also able to source a round cut diamond ring from its global supplier network. Browse our curated selection online and reach out to a Salon associate to schedule a viewing.
