When it’s first discovered, a raw diamond looks unremarkable: a clear pebble or rough crystal scarred by its journey from deep within the earth’s crust. It takes the diamond cutter’s art to release its brilliance, fire, and scintillation. The journey of a diamond from rough to the sparkling gem on your finger is surprisingly complex, using technologies developed over centuries.
As the hardest substance found on earth, diamond is the most challenging gem to cut. It wasn’t until the 15th century when it was first discovered that diamonds could be polished by their own dust. Before that, diamond rough and polished crystals were the only way to wear this gem. Faceting unlocked the potential for sparkle.
In 1475, a Flemish cutter named Lodewyk van Berquem invented the scaif: a diamond polishing wheel coated in oil and diamond dust with an arm above it to hold the diamond. Using this special cutting wheel he could not just polish diamonds but to actually cut facets and create brilliance.
Once cutters discovered the beauty of faceted diamonds, they kept innovating, starting by polishing crystals, cutting off the top of the crystal to create a table cut and then step cuts. In the 16th century faceted rose cuts were developed.
Mazarins, the first brilliant cuts with more facets to maximize brilliance, were developed in the middle of the 17th century for the French court of Versailles. In the eighteenth century, the mine cut was created to maximize the weight and beauty of the cut gems from the diamond crystals now available from mines in Brazil. When diamonds were discovered in South Africa, Brazil became the “old mine.” Old mine diamonds have the rounded square silhouette of the cushion with a high crown and deeper pavilion, similar to the shape of an octahedral diamond crystal.
Then the industrial revolution in the late 19th century transformed diamond cutting. New steam-powered machines and motorized saws allowed cutters to shape diamonds like never before: the round diamond was born. The Old European cut and English round cut had 58 facets, the same as round brilliants today.
Over the decades, cutters adjusted the proportions and angles to improve light performance. In 1919, a young Belgian student studying match in London, Marcel Tolkowsky, wrote Diamond Design, his thesis on the ideal proportions for round brilliant diamonds. Although his calculations omitted the girdle and needed to be adjusted, his work became the foundation for the modern round brilliant and the ideal diamond proportions still prized today.
Today diamonds are increasingly cut in sophisticated factories with high tech equipment rather than by hand. Most diamonds and almost all small diamonds are cut in India. Other important cutting centers are Israel, Belgium, and China.
Most cutters today work for surprisingly small margins, only one or two percent. Old-fashioned expertise is essential to making sure that each piece of rough is cut to unlock the highest possible value.
The yield for diamond rough is usually around 30%: that means a one-carat rough diamond will cut a one-third carat polished stone. Most of the carats of gem quality diamonds mined each year end up as dust, polished away during the cutting process.
The five basic steps to cutting a diamond are: sorting the rough, planning for manufacturing, cleaving or sawing the rough into a preliminary shape, shaping the girdle, and polishing the facets. Decisions at every step of the process affect the value of the final polished gem.
After diamonds are mined, they are sorted by hand and machine into categories by shape, size, color, and clarity in order to value them for sale. At the De Beers diamond sorting facility in Botswana, the world’s largest, experts divide rough diamonds from the mine into 12,000 different value categories, examining them in diffused daylight.
The manufacturing process is different for different types of rough: makeable rough, which will be polished into one stone; sawable rough, which will be sawn in two before polishing; near gem or cleavage rough, which needs to be cleaved into two or many more pieces before polishing, and last (and least) industrial grade diamond rough that will be cut into tools or crushed into powder.
Analyzing the diamond rough is the most complex step in the diamond cutting process and also the step that requires the most experience and technology. Should you cut one large round that will sell for more per carat but wastes more of the rough? Two smaller pears that sell for a lower price but waste less rough? What will give you the best yield? What is the current market value of all the possible gems that can be produced from this rough?
These complicated calculations are made by the marker, a very skilled cutter who weighs all the variables and decides whether a diamond should be sawn or cleaved into pieces and then marks exactly where the cuts should be made. With large valuable diamonds, this step can take months.
Today diamond cutters use sophisticated three-dimensional scans from Sarine machines to produce precise measurements, three-dimensional visualization, maps of inclusions, and estimates of the color and clarity of the final gem. The scan enable cutters to compare the size and quality of the gems that can be cut from each piece of rough with amazing precision.
Whatever shape the cutter chooses – round, princess, emerald, pear, heart, marquise, oval or baguette – there is no room for error once cutting begins.
If the cutting plan is to cut several gems out of the rough, the next step is to cut the diamond into pieces.
You know all those commercials where a cutter hits a rough diamond with a chisel and a hammer just right and it breaks in two? That is called cleaving: diamond crystals have a grain and a well-placed blow can break the diamond between the planes of the crystal. But going against the grain is very difficult. In order to cut against the grain, cutters use a circular saw with diamond dust for hours and hours or, increasingly today, a laser, which can burn through a diamond very quickly.
The shape of the final outline of each gem is created next in a process called bruting or girdling. To make a round diamond, a computer controlled bruting machine spins diamond against diamond.
Creating the outline of fancy shapes takes more time than a round diamond. The most difficult of all is creating the heart shape diamond, with its changing curves and deep cleft.
The final steps in the cutting process are faceting and polishing. Each facet is ground into the diamond by holding it in an arm called a tang against a spinning wheel called a scaif or scaife that is covered in diamond powder. The process is repeated for each facet, moving and angling the diamond precisely to keep the diamond perfectly symmetrical.
Faceting was once done manually but now relies heavily on computers to produce the proper size, angle, and symmetry of each facet. An error in the angle or placement in a single facet can result in light leaking out of the gem instead of being reflected back to your eye as brilliance so precision is crucial to the beauty of the final gem.
The diamond is than polished with fine diamond powder to smooth the facets, remove any polishing marks, and make sure that each facet is smoothly reflective.
A well-cut diamond reflects and refracts light, dancing with brilliance, fire, and scintillation. These unrivalled optics are due to careful cutting to make sure that the symmetry and proportions direct the maximum amount of light back to your eyes. Cut is the most important of the 4Cs of diamond quality. The beauty of modern diamonds is thanks to the perfection of the diamond cutter’s art.
