To celebrate two of the largest, purest white diamonds ever to come to auction, Sotheby’s takes a look at the art of diamond cutting - the process of sculpting a rough diamond and transforming it into a polished diamond. To find a rough diamond that allows the cutter to end up with a stone over 50 carats is a very rare discovery and to cut a perfect diamond over 50 carats is truly a masterpiece of both nature and man. The diamonds will be offered in the Magnificent Jewels and Noble Jewels sale (Geneva, 15 May).


A 51.71-CARAT ROUND BRILLIANT-CUT DIAMOND, ESTIMATE CHF 7.8–9 MILLION AND A 50.39-CARAT OVAL DIAMOND, ESTIMATE CHF 7–7.6 MILLION

With a single glimpse at any sculptural masterpiece such as Michelangelo’s “Pieta” or Rodin’s “The Kiss“, the observer is instantly left astonished by the raw power of form and emotion these magnificent figures impart. Through a slow and deliberate process, these master sculptors unlocked the inner beauty of the stone, slowly releasing a dimensional form and ultimately liberating the form from within a single block of material. Just as these artists painstakingly studied their dimensional canvases to craft dynamic forms, so to do diamond cutters as they cut away sections of the diamond and then polish it to reveal its inner brilliance and innate value.

Perhaps not often associated with the art of sculpting, diamond cutters are highly skilled sculptors in their own right. Through years of experience, a scholarly understanding of geology, patience and concentrated precision, these artisans have hatched the most dazzling gems in existence.

In 1375 the first guild of diamond cutters and polishers was established in Nuremberg, Germany. Called the Diamantaire, the guild developed various types of “cuts”: the shape and the quality of cut within the diamond. The first major development in diamond cutting came in the latter half of the 14th century with the creation of the “Point Cut”. This cut follows the natural shape of an octahedral rough diamond crystal, eliminating waste during the cutting process. This art has evolved greatly over the past several hundred years.  With the use of advanced technology, diamonds cut today are an art of precision.


THE BLUEPRINTING STAGE: ASSESSING WHERE TO CUT THE 425 CARAT ROUGH

There are several factors that must be analysed during the planning stages of cutting. A foremost consideration is how to cut the stone to maximise its value. Both the popularity of certain shapes among consumers as well as physical factors such as the shape of the rough stone, location of inclusions and flaws determine shape. Scanning devices and 3-dimensional models are used to find an optimal way to cut the stone.

Typically, round and square brilliant cuts are preferred when the crystal is an octahedron, as often two stones may be cut from one crystal. Oddly shaped crystals, such as macles are more likely to be cut in as a fancy cut. Secondly, weight retention analysis must be assessed to find the best combination of the finished stone and how it relates to per carat value. Even with modern techniques, cutting and polishing a diamond always results in dramatic weight loss, about 50%. Finally, colour retention is studied in the rough as it will influence the colour grade of the diamond, either increasing or decreasing its value. 

Once the diamond is assessed and the cutter commits to a blueprint, the first step is to cleave or saw the rough into separate pieces to be completed as separate gems.  Bruting is the process where a diamond cuts a diamond; two diamonds are set onto spinning axels turning in opposite directions, which are set to grind against each other to shape each diamond into its intended shape.  Once the diamond begins taking shape, the cutter then polishes the diamond, cutting facets onto the diamond whereby unlocking its inner brilliance.  Finally, the diamond is cleaned using acids, followed by a thorough examination process to grade its cut, colour, clarity and carat weight. 


FROM ROUGH TO REFINED: POLISHING THE DIAMOND’S FACETS   

Today, diamond cutting is concentrated in a few cities around the world. From diamond trading centers such as Antwerp and Tel Aviv to processing centers and finally to places like New York City where a majority of the most important diamonds in the world are cut, these cities hold the artisans that unlock a diamond’s inner beauty; a beauty that has inspired emotion for thousands of years.

These remarkable diamonds will be available to view, alongside other major highlights from the Magnificent Jewels & Noble Jewels sale on the following dates:

SINGAPORE
Friday, 27 April 18 | 10:00 AM - 05:00 PM SGT
Saturday, 28 April 18 | 10:00 AM - 05:00 PM SGT

TAIPEI
Tuesday, 1 May 18 | 10:00 AM - 05:00 PM CST
Wednesday, 2 May 18 | 10:00 AM - 05:00 PM CST

DUBAI
Tuesday, 1 May 18 | 10:00 AM - 08:00 PM GST
Wednesday, 2 May 18 | 10:00 AM - 08:00 PM GST

GENEVA
Friday, 11 May 18 | 10:00 AM - 06:00 PM CEST
Saturday, 12 May 18 | 10:00 AM - 06:00 PM CEST
Sunday, 13 May 18 | 10:00 AM - 06:00 PM CEST
Monday, 14 May 18 | 10:00 AM - 06:00 PM CEST
Tuesday, 15 May 18 | 10:00 AM - 04:00 PM CEST