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Diamond cutting is the practice of shaping a diamond from a rough stone into a faceted gem. Cutting diamonds requires specialized knowledge, tools, equipment, and techniques because of its extreme difficulty.
The first guild of diamond cutters and polishers (Diamantaire) was formed in in Nuremberg, Germany,[1] and led to the development of various types of "cut". This has two meanings in relation to diamonds. The first is the shape: square, oval, and so on. The second relates to the specific quality of cut within the shape, and the quality and price will vary greatly based on the cut quality. Since diamonds are one of the hardest materials, special diamond-coated surfaces are used to grind the diamond down. The first major development in diamond cutting came with the "Point Cut" during the later half of the 14th century: the Point Cut follows the natural shape of an octahedral rough diamond crystal,[2] eliminating some waste in the cutting process.
Diamond cutting, as well as overall processing, is concentrated in a few cities around the world. The main diamond trading centers are Antwerp, Aviv, and Dubai from where roughs are sent to the main processing centers of India and China.[3] Diamonds are cut and polished in Surat, India and the Chinese cities of Guangzhou and Shenzhen.[4] India in recent years has held between 90% of the world market in polished diamonds and China has held the rest of the world market share in a recent year.[3] Other important diamond centers are New York City and Amsterdam.[5]
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The basic diamond cutting process includes these steps; planning, cleaving or sawing, bruting, polishing, and final inspection.[6] A simplified round brilliant cut process includes the following stages:
This is just one, although a fairly common way of creating a round brilliant cut. The actual process also includes many more stages depending on the size and quality of the rough stone. For example, bigger stones are first scanned to get the three-dimensional shape, which is then used to find the optimal usage. The scanning may be repeated after each stage and bruting may be done in several steps, each bringing the girdle closer to the final shape.
It is possible only because the hardness of diamond varies widely according to the direction in which one is trying to cut or grind.
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Diamond manufacturers analyze diamond rough from an economic perspective, with two objectives steering decisions made about how a faceted diamond will be cut. The first objective is that of maximum return on investment for the piece of diamond rough. The second is how quickly the finished diamond can be sold. Scanning devices are used to get a 3-dimensional computer model of the rough stone. Also, inclusions are photographed and placed on the 3D model, which is then used to find an optimal way to cut the stone.
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Man-powered diamond cutting mill in 18th centuryThe process of maximizing the value of finished diamonds, from a rough diamond into a polished gemstone, is both an art and a science. The choice of cut is influenced by many factors. Market factors include the exponential increase in value of diamonds as weight increases, referred to as weight retention, and the popularity of certain shapes amongst consumers. Physical factors include the original shape of the rough stone, and location of the inclusions and flaws to be eliminated.
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The weight retention analysis studies the diamond rough to find the best combination of finished stones as it relates to per carat value. For instance, a 2.20-carat (440 mg) octahedron may produce (i) either two half-carat (100 mg) diamonds whose combined value may be higher than that of (ii) a 0.80-carat (160 mg) diamond plus a 0.30-carat (60 mg) diamond that could be cut from the same rough diamond.
The round brilliant cut and square brilliant cuts are preferred when the crystal is an octahedron, as often two stones may be cut from one such crystal. Oddly shaped crystals, such as macles are more likely to be cut in a fancy cut'that is, a cut other than the round brilliant'which the particular crystal shape lends itself to.
Even with modern techniques, the cutting and polishing of a diamond crystal always results in a dramatic loss of weight, about 50%.[7] Sometimes the cutters compromise and accept lesser proportions and symmetry in order to avoid inclusions or to preserve the weight. Since the per-carat price of a diamond shifts around key milestones (such as 1.00 carat), many one-carat (200 mg) diamonds are the result of compromising cut quality for carat weight.
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The 253-carat Oppenheimer Diamond'an uncut diamond does not show its prized optical propertiesIn colored diamonds, cutting can influence the color grade of the diamond, thereby raising its value. Certain cut shapes are used to intensify the color of the diamond. The radiant cut is an example of this type of cut.
Natural green color diamonds most often have merely a surface coloration caused by natural irradiation, which does not extend through the stone. For this reason green diamonds are cut with significant portions of the original rough diamond's surface (naturals) left on the finished gem. It is these naturals that provide the color to the diamond.
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The other consideration of diamond planning is how quickly a diamond will sell. This consideration is often unique to the type of manufacturer. While a certain cutting plan may yield a better value, a different plan may yield diamonds that will sell sooner, providing an earlier return on the investment.
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Cleaving is the separation of a piece of diamond rough into separate pieces, to be finished as separate gems. During the planning stage, diamond manufacturers identify cleavage planes, and use those planes to decide how to split the diamond. Diamond manufacturers make a groove in the diamond with a laser or saw or another diamond, and then split the diamond by placing a steel blade in the groove and giving a gentle tap.[8] Cleavage can be along any of the four planes parallel to the faces of an octahedral diamond (i.e. perpendicular to body diagonals of the unit cell).[9]
Sawing is the use of a diamond saw or laser to cut the diamond rough into separate pieces. Unlike cleaving, this step does not involve cleavage planes. This step gives diamonds their initial shape.
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Bruting is the art of cutting a diamond to make the girdle round. In the modern era diamonds are rounded using either a laser, a diamond disk impregnated with diamonds, or spinning two diamonds so they cut against each other. Industrial diamonds can also be used for bruting a diamond round. Modern computer software measures the roundness of each diamond and ideal cut diamonds have to round within a tenth of a millimeter to qualify as an excellent cut diamond.
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Diamond polisher in Amsterdam. Polishing is carried out by forcing a diamond against a spinning disk with abrasive.Diamond polishing is the final polishing of the diamond. In a diamond factory, one would find a diamond crossworker who first places the main facets on a diamond (blocking the diamond). This is done to ensure maximum weight, clarity and best angles for the specific shape of diamond. After initial crossworking is complete, the diamond is finalized by smoothing the main facets by the crossworker, which is known as polishing the diamond. After the main facets have been polished by the crossworker, the final facets are polished onto the diamond by a brillianteer. The facets added are the stars, top and bottom halves are also known as upper and lower girdle facets.
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The final stage involves thoroughly cleaning the diamond in acids, and examining the diamond to see whether it meets the quality standards of the manufacturer.
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Due to changes in market desirability and popularity, the value of different styles of diamond fluctuates. All diamonds can be recut into new shapes that will increase value at that time in the market and desirability. An example of this is the marquise cut diamond which was popular in the s to s. In later decades, jewelers had little success in selling this shape in comparison to other shapes like the oval or pear shape.[citation needed] The marquise can be cut into an oval diamond by any diamond cutter with a loss of 5 to 10% in total weight.[citation needed] For example, a 1.10-carat marquise shape would be a 1.00 oval cut diamond by rounding the sharp points and creating an oval which currently in the market has a much greater desirability and resale value. The same marquise shape also could become a pear shape instead by only trimming and rounding the side which will be turned into the base of the pear shape.
In the 18th century there was a trend for recutting Indian diamonds to suit English tastes. The Koh-i-Noor's original cut weighed a little over 186.00 carats. When it was recut to an oval-shaped brilliant, almost 80 carats were lost.[citation needed]
Other aspects are affected in recutting for value as well, such as the clarity. If an original shape contained inclusions on the tips, the recut would yield an increase in clarity since trimming down to a new shape would yield a cleaner overall finished diamond.[citation needed]
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By
Bryan Boyne (g.g.)
The process of cutting of a rough diamond crystal into a finished gem is sometimes referred to generally as diamond polishing. While the process of crafting a polished diamond involves many different steps, the final polishing of all the facets is a crucial step in determining the quality and beauty of the finished gem.
A rough diamond crystal before it has been polished
Before the actual final step of polishing, a rough crystal must be planned, sawn, and shaped. Each rough diamond offers a unique challenge. Determining the best approach requires careful analysis of the potential of the crystal which involves a complex calculus involving clarity features, shape and orientation the crystal, and the economics of different potential yield scenarios. The crystallographic orientation is a critical consideration in the plan as certain directional planes differ in hardness making it impossible to polish in certain directions.
Hand drawn markings on a rough diamond crystal marking cut lines
Planning has been significantly aided in recent years by advance scanning hardware coupled with sophisticated computer software. Once the plan is decided upon, the crystal is sawn into the pieces that will eventually become individual diamonds. Each of these pieces is then blocked into basic shapes.
Screen shot from diamond planning software showing how three diamonds can be cut from an actual piece of rough considering clarity features and crystallographic orientation.
Illustration of two princess cuts that can be produced from an octahedral diamond crystal
Illustration of two different potential yield scenarios from a single crystal
The main cutting instrument is the cutting 'wheel' called a scaife ' a disk impregnated with diamond powder that turns at rpms. The diamond is held against the scaife in a device called a tang.
Scaife with tang holding diamond crystal
The first basic facets that are placed on the diamond with the cutting wheel determine the overall proportions and outline of the diamond. Proper proportions are critical to the eventual light performance (and beauty) of the polished diamond as they will determine the internal reflection and refraction of light within the diamond and back to the eye, as well as how much light will be lost to leakage.
After the main facets are placed on the diamond, the ancillary facets are cut. Finally, every facet is polished to a mirror finish, or as perfect a finish as the crystal will allow. Certain aspect of the crystal will influence the ultimate finish that can be achieved. Things like graining in the crystal may make a mirror finish on some facets difficult or impossible.
Stages of the Diamond Polishing Process
A mirror finish enables the diamond to possess as much external luster as possible and optimizes the internal reflection of light rays as they bounce from facet to facet before being returned to the eye of the observer. Light rays exiting from a facet with an imperfect polish are degraded in terms of dispersion (fire) or brightness (brilliance). Facets that do not have a high polish are also prone to accumulating dirt and oils that result in further loss of performance. Diamonds with inferior polish require more frequent cleaning in order to look their best.
Polish and symmetry are the two factors of finish that are assessed on a laboratory grading report . A diamond graded as having Ideal polish indicates that each and every facet on the diamond has a mirror finish.
A polished diamond is a tiny system of mirrors. A well designed facet structure will capture and return a high percentage of light entering through the crown, bounce it around internally and then return it to the eye with a dazzling display of brilliance and fire. Corresponding facets need to be in three dimensional alignment (sometimes referred to as optical symmetry or optical precision) in order for that to happen to the fullest extent possible. Facet arrangements that are not optimized for light handling, or failures in execution by the diamond cutter, result in polished diamonds that are deficient in capturing the full beauty of the gem. An in-depth look at the magical property of diamond fire reveals how this miniature system of mirrors operates.
A problem that has plagued the diamond cutting industry for over a hundred years is the philosophy of maximizing yields at the expense of light performance and beauty. What is truly special about diamonds, in addition to their rarity and durability, is their unsurpassed potential for fire and brilliance. It is the design and craftsmanship of the cutting and polishing that determines whether a given diamond will fulfill this promise. Compromises in proportioning and precision result in deficits in optical performance. And these compromises are routinely made in order to retain the most carat weight out of the starting rough.
Exactly how this philosophy arose and was perpetuated in the diamond trade is the subject of a fascinating historical account by Al Gilbertson. In his book American Cut: The First 100 Years we learn that the early cutters from Europe were paid a wage based upon how much finished weight in polished diamonds they could retain from the roughs that were supplied them by their shop owner. Although there were a few pioneers even in those very early days who insisted on cutting for beauty, the status quo would prevail and to a significant degree, continues to persist to this day.
As mentioned in Mr. Gilbertson's book, one of those early pioneers and champions of cutting for beauty was Robert Morse who was fond of saying 'Shopping for diamonds by the carat is like buying a racehorse by the pound!'
While most diamond manufacturing is still driven by yield, a few modern cutters and retailers have dedicated themselves to the goal of maximizing light performance and beauty. The more expensive practice of forgoing some carat weight for the goal of producing the finest performing diamonds has given rise to a relatively small niche of merchants offering Ideal and Super Ideal cut diamonds. A diamond report from the American Gem Society Laboratories (AGSL) is the document of choice for these demanding merchants. AGSL has the most scientifically advanced cut grade system in the market. It uses sophisticated ray tracing technologies to measure the fundamental aspects of light performance; brightness, contrast, dispersion and leakage. Only diamonds with no significant deficits in any of these aspects can earn a grade of Ideal.
The super ideal category is even more restrictive. The stringent requirements for this designation involve assessment of three dimensional precision and other characteristics that further distinguish this elite category from Ideal diamonds. The A CUT ABOVE® is one of the most celebrated of the super ideal brands and features a full set of published specifications and qualifications making these diamonds some of the finest ever brought to market.
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