The Diamond Cutting And Polishing Process

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.
Rough Diamond Crystal
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.
Rough Diamond Crystal Planning
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.
Diamond Planning
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.
Diamond Rough Illustration
Illustration of two princess cuts that can be produced from an octahedral diamond crystal
Yeild Potential of a Single 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 4000 rpms. The diamond is held against the scaife in a device called a tang.
Scaife with Tang holding Diamond Crystal
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.
Diamond Polishing Stages
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.
Ideal Cut Diamonds
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 Tiny Sculpture of Mirrors

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.

Diamond Cutting For Weight Over Beauty

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!”

Ideal and Super Ideal Cut Diamonds

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.
Super Ideal Diamonds
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.

Find Your Perfect A CUT ABOVE® Super Ideal Cut Diamond

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