Jewelry In Focus

Discovering the Gemology of Diamonds at L’École Van Cleef & Arpels

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Continued from Exploring the Science of Diamonds at L’École Van Cleef & Arpels

After our espresso-fueled break, we returned to our classroom to learn how man has tamed the invincible diamond. First step, figure out how to cut the hardest material on earth.

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The true beauty of a diamond is difficult to glean from the diamonds rough octahedral form, so man first learned how to polish the surface of the stone. Since only a diamond can cut or polish another diamond, early polishers used wood or iron wheels coated with a thin layer of fat (diamonds are lipophilic) sprinkled with diamond dust. This initial cut was called the point cut which closely followed the diamond roughs octahedral shape. As people learned more about diamonds, they discovered that by polishing down the point of the octahedron, creating a ‘table’, resulted in a more lustrous stone. The table cut was the crude original that would pave the way to the modern brilliant cuts we see today.

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Cleaving is a vital facet of the diamond taming process. While a diamond may be the hardest mineral, it is not the toughest. The diamond’s crystal structure produces perfect cleavage, resulting in smooth fractures when force is applied along the appropriate crystal planes.

Joseph Asscher prepares to cleave the Cullinan diamonds

Joseph Asscher prepares to cleave the Cullinan diamonds. Photo courtesy of Artemisia’s Royal Den

Mr. Dufermont shared one of the most famous moments in diamond cleaving history. Joseph Asscher, a renowned artisan in the industry who developed the Asscher cut, was selected to cleave the 3,106-carat rough Cullinan diamond in 1905. In order to yield the large diamonds determined from the rough, Asscher needed to hit the Cullinan in precisely the right place. When made the initial strike, in front of a notable audience, he fainted. Apparently, the sound that resulted from the blow was unlike anything he had ever heard throughout his long career, so he believed something had gone disastrously wrong. After he regained consciousness, he saw that his blade had broken while the diamond remained perfectly intact. Asscher would later cleave the Cullinan into nine large diamonds and several small stones with a larger, stronger blade.

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The nine numbered Cullinan Diamonds in their rough shapes (left) and after polishing (right). Photo courtesy of Artemisia’s Royal Den

While cleaving the rough generates the basic template for a faceted diamond, it is the cutting process that really makes the diamond sparkle. From the simple table cut evolved the round brilliant cut, the modern standard established by Marcel Tolkowsky in 1919. An engineer by education, Tolkowsky calculated the ideal proportions of the round brilliant cut that delicately balanced both brilliance and fire. Today, the modern round brilliant cut emits that classic fiery sparkle through a total of 57 facets (or 58 if a culet facet is present) in the ideal proportions in the diagram below.

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Optimizing the most of a rough diamond was a skill reserved for experienced experts who had a innate eye for visualizing faceted diamonds within the rough. However, some 60 to 70 percent of the stone is lost when performed by humans. Today, advanced scanners now analyze a majority of rough diamonds and propose the most optimal cuts, a process resulting in only 30 to 40 percent carat weight loss.

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Most diamonds are cut as round brilliants, however there are many other cuts of the diamond as well. One cut in particular was inspired by the lips of a mistress. According to legend, the marquise diamond was commissioned by Louis XV to resemble the smile of his mistress, the Marquise de Pompadour. Other popular cuts include oval, emerald, Asscher, pear and heart.

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Next, we learned the importance of evaluating diamonds, particularly the diamond’s color. For diamonds in the normal color range, their color is graded on a scale from D to Z, where D is perfectly transparent with no tint of color. We were given a box with four cubic zirconia of slightly varying color grades. With tweezers in hand, we were tasked with arranging the stones from colorless to off color. Easy enough you would think, but they ranged from D to G in color. Though much of the processes for evaluating a diamond can be done or aided by technology, color grading can only be determined by comparison with the human eye.

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After tackling the color task, clarity was up next. Clouds, feathers, knots, and cavities may have no relation to one another in their general meaning, but when it comes to diamonds all are types of inclusions. Our next challenge was to determine the clarity of three diamonds by arranging them from least included to most using the standard clarity grading scale: FL (flawless), IF (Internally Flawless), VVS1 (Very Very Slightly Included), VVS2, VS1 (Very Slightly Included), VS2, SI1 (Slightly Included), SI2, I1 (Included), I2, I3. With jewelry loupes in hand, we set about finding minute inclusions in the small diamonds.

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The last portion of the class looked at diamond modification, such as heat treatments to affect color and laser treatments to improve clarity, and the efforts of man to create synthetic diamonds. The latter has come a long way in recent years through the methods HPHT (High Pressure, High Temperature) and CVD (Chemical Vapor Deposition). If we can economically grow diamonds for various industry uses, the applications of the diamond are limitless. Ample research and testing has opened new frontiers for diamonds, including semiconductors and optical uses.

Overall, I not only enjoyed the experience but left with a deeper understanding of and appreciation for diamonds. I highly recommend this class at L’École Van Cleef & Arpels as well as the many others offered in the curriculum. There are still a few seats left in a few of the classes before the New York session is over on June 18th!

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