A Cut Above: How a Centuries-Old Practice Affects Every Diamond

By Thomas Forwood
Three prominent stones feature in Sotheby’s upcoming Magnificent Jewels and Jadeite auction in Hong Kong: an emerald-cut diamond of 80.88 carats, a brilliant-cut diamond of 10.88 carats and a pear-shaped yellow diamond of 10.88 carats. The auspicious carat weights occur not by chance but by design – realized in an art form that is meditative, metaphoric, and often mystical in its character.

T he finest gemstones in the world are a collaboration between humankind and nature. Deep within the earth, rough gemstones are created under tremendous heat and pressure, subject to infinite random fluctuations in physical and chemical conditions that alter their shape, size, colour, clarity, and level of imperfections, making each one unique. And yet, for all the effects of nature, it is the final touches, deftly applied by skilled human hands, that are the most important and essential characteristics to many discerning jewel-lovers. It is the cut of a gemstone that reveals the majesty inside.

The cut of a stone, more than referring to its general shape, is the adherence to the optimum angles, proportions, and symmetry that optimises its brilliance. Such is the skill needed to perfect a stone’s cut that it requires years of training and apprenticeship before a diamond cutter is permitted to cut and polish a rough diamond. There is no room for error. Each and every cut instantly affects the brilliance and value of the diamond. One wrong move and the gem could be ruined permanently.

Typically, 50% of a stone can be lost by cutting. One of the most famous illustrations of the importance of diamond cutting is the historic Indian stone, the Koh-i-Noor diamond, the cutting of which became a public event and captured the public’s imagination. When it was exhibited at the 1851 Great Exhibition, it left the public unimpressed, who saw it as a dull-looking stone, and distinctly underwhelming. Despite attempts to highlight the stone using a variety of theatrics, eventually Prince Albert ordered it to be recut. The 186-carat stone became the Oval brilliant 105.6 carat stone we know today. The 43% sacrifice in weight was worth the added visual quality.

There are parts of the cutting process that are done using machines, but a skilled diamond cutter is still needed to do some very particular things. Even with the mapping done by a computer, the cutting of the stone to get the correct angles is done by hand. It is a slow business, very delicate, and takes many days. There’s a few people involved in the process, but the final person is called a Brillianteer, who puts in the final facets (the smooth planes) and makes it sparkle.

Fancy cuts include Baguette, Marquise, Emerald Cut, Oval, Briolette and Square. More modern cuts that have been developed are the Radiant Cut (created in 1977) and the Princess Cut (created in 1980). Of course, new developments in diamond cutting are always being made. In December 2018, Sotheby’s sold a ring made entirely of diamond that had 2,000–3,000 facets.

Gemstones with carat weights that have an abundance of the number eight in their digits seem particularly felicitous, appealing to the sensibilities of the Asian market today. Three important diamonds in Sotheby’s upcoming auction in Hong Kong all have auspicious weights ending in a perfect 0.88 carats.

Despite technical advances, diamond cutting has, for centuries, been considered a true art form.

Today, diamonds are still seen as the stones of romance and prized above all others by many, and choices are always made when deciding upon the perfect item of jewellery or gemstone. One can look at beauty and rarity, provenance and craftsmanship, even weight, but in the end, buying a jewel is one of the most personal purchases an individual can make, and the individual is almost always the best judge of the worth to them. There is tremendous power in diamond cutting, transforming a rough crystal into a treasure filled with light and life. Today, a high degree of skill is involved in achieving the perfect brilliant or fancy cut, aided by modern technology including lasers and computer optics, and yet some of the world’s most skilled diamond cutters maintain their own “secret” recipes for the abrasive diamond dust that is critical to the process. Just in case.

Stay informed with Sotheby’s top stories, videos, events & news.

Receive the best from Sotheby’s delivered to your inbox.

By subscribing you are agreeing to Sotheby’s Privacy Policy. You can unsubscribe from Sotheby’s emails at any time by clicking the “Manage your Subscriptions” link in any of your emails.

More from Sotheby's