How Are Diamonds Cut and Polished?

December 21, 2023

To those who have never seen one, an original rough diamond looks like an unassuming, cloudy stone with little value. However, what is hidden underneath, waiting to be brought out into the light, is a breathtaking diamond with mesmerizing sparkle, fire, and brilliance. How can a stone transform into something of such beauty? Of course, it isn't magic, although sometimes it appears that way when comparing a piece of diamond to the finished product.
Through the artistry of diamond cutting and polishing, a diamond's true nature is revealed, and nature's hidden masterpiece is exposed. The process is painstaking; every decision is meticulous, and every move is precise. In the world of diamonds, the terms "diamond cut" and "polish" aren't just technical jargon—they are the keys to unlocking these precious gems' true beauty and value.
In this article, we'll explore the intricate process, artistry, and science used to turn a rough stone into a polished diamond.


The Diamond Cutting Process

From start to finish, the diamond manufacturing process involves many players, beginning with those who mine diamonds to diamond cutters and polishers to diamond jewelers and retailers.


Unearthing Rough Diamonds

Rough diamonds live deep within the Earth's mantle, some 150-200 kilometers below the surface. Over millions of years, intense heat and pressure - exceeding 50,000 times the atmospheric pressure - transform ordinary carbon atoms into shimmering crystals. In some cases, trace elements, such as nitrogen, sulfur, and boron, interact with carbon atoms during the diamond's formation, resulting in naturally colored diamonds that span the rainbow from pink to blue to green and even black.

Mining these treasures is no easy feat. Some diamonds surface in kimberlite pipes that carry them up from the mantle. Open-pit mines follow these pipes, meticulously sifting through tons of rock to uncover a few carats with sparkling potential. Others lie near riverbeds or on the ocean floor, carried there by ancient erosion, and require specialized heavy machinery to separate diamonds from the sediment.

How Are Diamonds Cut and Polished rough diamonds

The Diamond Cutting and Polishing Process

Once unearthed, rough diamonds make their way into the talented hands of professional diamond cutters, highly trained professionals with a discerning eye and a steady hand. The diamond cutting and polishing process can be broken down into five steps: planning, cleaving, bruting, diamond polishing, and inspecting.


Diamond Planning

Master diamond cutters conduct a thorough analysis, studying the diamond rough to meticulously understand each grain, inclusions, and potential cleavage planes, mapping a path that maximizes the diamond's yield and brilliance while preserving its unique character. Like fingerprints, no two diamonds are the same. This initial assessment is crucial to determine the best shape for the diamond, which has little to do with the shape of the rough stone.

Today, diamond cutters use a Sarin machine to create a 3D computer model of the rough stone, map it, and get accurate measurements. Even with modern technology, over 50% of the rough stone is lost as the diamond is cut and polished, ending up as diamond dust on the floor.

How Are Diamonds Cut and Polished


The process of cleaving involves splitting the piece of diamond rough crystal into separate segments, enabling cutters to concentrate on individual pieces for optimal yield. At times, cutters employ diamond saws, equipped with blades coated in diamond powder, to meticulously shape the rough diamond crystal into specific forms, moving beyond traditional cleaving methods. These diamond saws are particularly effective in precisely crafting the desired cut stone. Additionally, cutters might turn to advanced laser cutting tools for rough diamonds with challenging shapes. These high-tech solutions ensure the utmost precision and minimal waste when working on a diamond crystal, achieving the perfect cut stone.


Mechanical Bruting

The diamond's basic form emerges during bruting, where rough edges are smoothed and refined. This step, also called girdling, involves mounting two rough stones on a spinning axle, facing each other. As the axle whirls, the diamonds grind against each other in opposite directions, letting friction sculpt their outer edges into rough circles.


Polishing the Diamond

The polishing stage is about forming facets and creating flat, smooth surfaces that maximize the gem's light reflection and brilliance. Polishing happens in two parts: blocking and brillianteering. First, the cutter uses a diamond-tipped wheel on a rotating arm to grind and polish eight main pavilion facets (bottom), eight crown facets (top), a culet (tiny point cut at the bottom), and a table facet (flat top). These initial facets form the basic structure and act as a precise template for the next step.

The second stage, brillianteering, involves adding the remaining facets, bringing the total to 57 for the classic round brilliant cut. This is a critical step, as the placement and angle of each facet directly determine how the diamond interacts with light, influencing its fire, brilliance, and scintillation. This step demands incredible precision to ensure each facet aligns perfectly with the template from the blocking stage to achieve optimal light performance.

How Are Diamonds Cut and Polished

Inspecting and Grading Polished Diamonds

After all the cutting and polishing is complete, experts inspect the finished diamond to ensure it matches the manufacturer's specifications. If needed, the stone can be touched up by polishers. Finally, the diamonds are sent to a gemological lab such as the GIA or IGI, which verifies the carat weight, evaluates the stone, and issues a grading report.


Ideal Cut Diamonds

The most common ideal cut diamonds are round, brilliant, or princess cut. As the name suggests, they have ideal proportions and angles and earn excellent polish and symmetry ratings. An ideal cut diamond can reflect and refract nearly all the light that enters it, which produces the fire and brilliance seen in the stone.

The ideal cut was invented in the 1900s by Belgian diamond cutter Marcel Tolkowsky. While his calculations still serve as a guide, many modern diamond manufacturers augment it with computer models and technological scopes.

This2.02 carat princess shaped diamond reflects light beautifully:

2.02 carat princess shaped diamond

Cut, Carat, and Clarity: Which Is the Most Important?

Diamond cuts are graded on a scale from Excellent or Ideal to Poor. A diamond's cut is a quality marker. Unlike other aspects of the 4 Cs (clarity, color, and carat weight), where optimal value overlaps with aesthetic appeal, a diamond's cut is a different beast. With clarity, for instance, after a certain grade, there is minimal visual improvement to the naked eye but a substantial price jump. A VS1 or VS2 diamond will likely appear eye-clean to most, making the upgrade less impactful.
Cut, however, is the "must-have" C. While imperfections in clarity or color can be subtly disguised, and even smaller diamonds can radiate beauty, a poor diamond cut can rob a gem of its light-bending magic and, ultimately, its captivating sparkle. We don't advise compromising cut quality for carats or choosing a cut below Good.


Diamond Shapes: Colored Diamonds VS. Colorless Diamonds

How the stone is cut and shaped can affect the sparkle and color of the diamond. Interestingly, round colorless diamonds look the 'whitest,' and round brilliant cut diamonds reflect the most light.

When it comes to colored diamonds, fancy shapes enhance their natural color. This is why you will often find natural green color diamondspink color diamonds, and yellow color diamonds in these shapes. When selecting a colored diamond, consider opting for pear, oval, and marquise cuts. These shapes excellently cut the diamond to enhance its color and brilliance. 

Moreover, diamonds can be cut in various shapes, each offering unique characteristics. While the round brilliant cut is famous for maximizing sparkle, square shapes like the radiant cut provide a different aesthetic. The radiant cut is an example of a shape that merges the brilliance of a round cut with a more modern feel. Oval cut diamonds achieve elegance by rounding the edges, offering a softer alternative to the round cut. Similarly, with its elongated shape, the marquise cut diamond makes a striking choice, often appearing larger than other cuts of the same carat weight.

Certain cut shapes are used more frequently for specific colored diamonds. For instance, green color diamonds are most often found in round or cushion cuts to enhance their rare hue. On the other hand, a poorly cut diamond, regardless of its shape, can diminish color and brilliance, underscoring the importance of expert cutting and shaping a diamond. Each shape and cut, whether for colorless or colored diamonds, is pivotal in bringing out the best in the stone, transforming it into a dazzling work of art.

Check out this amazingmarquise cut blue diamond:

marquise cut blue diamond

A Diamond's Journey from Rough to Polished Diamond

The next time you admire the sparkle of a diamond, remember the journey it's taken. From the depths of the Earth to the skilled hands of artisans, each facet tells a story of skill and artistry. When searching for your ideal diamond, always check the stone's cut grading and see how it reflects light under different conditions.

Cutting a diamond begins with the diamond rough, where master cutters analyze to find the optimal way to cut the stone. This is a crucial stage, as how a diamond is cut can significantly influence its final beauty and value. Often, diamonds are cut using another diamond, as it is one of the few materials hard enough to split the diamond rough effectively.

In pursuit of perfection, sometimes the result of compromising cut quality is a diamond cut in a fancy shape. This requires skillful hands who can cut and shape precisely. The diamond is placed on a cutting wheel for the final polishing, where all facets are polished meticulously. This process must be done carefully, as each facet's angle and finish contribute to the diamond's overall brilliance and fire.
Remember, every polished diamond you see results from a long and intricate journey, from being found as a rough diamond to its transformation into a dazzling gem.

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