A New Approach to Assessing Cut Quality

I once heard the opinion that the quality of a cut is primarily determined by the quality of the polish. I couldn't agree more, but let me elaborate.
The term "precision cut" has become very popular recently. Let's try to understand what it means from the perspective of different market participants and how precise one cut is compared to another. I've heard different definitions. Some say precision cutting is done on automatic machines—using the same design, the same size, and with the same imperfections. Others characterize such gemstones as more or less symmetrical ones with a small "window" (!) and a medium polish, but rare and quite valuable. Still others say a precision cut must be innovative, incorporating concave facets and even carving elements: the more complex the design, the more precise the cut. Finally, some experts believe that precision cutting is anything that deviates from standard shapes. How can these opinions be reconciled?

Let's start with a definition. According to this expression, a precision cut must be, first and foremost, precise. Only precise. Not innovative, not artistic, not valuable—simply precise. This means the gemstone must be free of cutting flaws—I mean noticeable flaws. This raises two questions: what does "cutting flaws" mean, and how noticeable can they be?

To answer the first question, let's imagine our gemstone has a "perfect cut"—without the slightest deviation. Let's consider it not only as a whole, but also as a complex of individual design elements—design points such as facets, edges, intersection points (where four or more facets meet), and pairs of symmetrical facets (according to the original cut design). Each design point on a real stone may differ from the ideal model. For example, a facet surface may have scratches, pits, irregularities, cracks, and so on. Edges may not be straight, but chipped or rounded—that is, not sharp and reflective. Intersection points may not be points, but additional edges. Finally, identical facets—for example, the main facets in a standard brilliant cut—may also differ in size or shape. Optical effects such as "windowing" or light suppression are a different matter altogether.

Regarding the level of visibility, it would be logical to divide these defects (or deviations from the ideal model) into several categories. Indeed, the tiniest scratch, barely noticeable even under 10x magnification, should have a much lesser impact on the cut quality assessment than a scratch clearly visible under a loupe, especially if the scratch is so deep and noticeable even to the naked eye. A tiny, almost invisible chip on the girdle is not as significant as a missing piece measuring half a millimeter. A 10x loupe can be used as a tool for identifying such defects.

Another important point: the visibility of cut defects (especially on facets and facet joints) depends on lighting. For example, tiny polishing scratches ("cat hairs") are clearly visible under a spotlight—such as an LED or incandescent lamp—but completely invisible under the diffused light of a gemological lamp. To assess the precision of a cut, it's necessary to use lighting that makes the defects most visible. Of course, the expert requires knowledge and experience in how to observe and direct the light.

Some experience in assessing cut quality has already been accumulated through technical cutting competitions held by cutting guilds in various countries, such as the United States, England, Australia, and Thailand. The rules and evaluation criteria in these countries vary in detail, but not significantly – cut perfection is assessed on a 100-point scale; similar assessments are made for facets, edges, facet joints, and symmetry. However, these rules and criteria must be adapted to market conditions if they are to be used to assess cut quality overall.

I recently introduced such a cut quality grading system in collaboration with GIT and AIGS. The method is quite simple: a gemstone is considered as a collection of design elements (pattern points), which are the aforementioned facets, edges, facet joints, and facet pairs of identical shape and size, consistent with the symmetry of the selected design. If any design element contains a defect (a chip on an edge, a scratch on a facet, etc.), points for the defects are entered into a special table, depending on the size of the defect (or, more accurately, its visibility):
a) barely noticeable at 10x magnification;
b) clearly visible through a magnifying glass and barely noticeable with the naked eye;
c) clearly visible to the naked eye.

Each error point category is weighted toward the final grade: 25%, 50%, and 100%, respectively. However, only the design elements with defects should be considered, not the defects themselves. For example, if one facet has two or more scratches, only one point should be added for each defect, assigning it the weight of the largest defect. After analyzing and entering all the design points with various defects into the spreadsheet, the spreadsheet calculates the final cut quality assessment on a 100-point scale with four decimal places.

I can add that the final score itself doesn't tell non-professionals much.

To understand all possible outcomes, we classified and divided them into three classes, each of which also has three subclasses. The subclasses of the two lower classes are designated by numbers (e.g., Commercial-I or Quality-III). However, each subclass of the highest (elite) class has its own name – Elite Premium, Elite Extra, and Elite Ideal. To qualify for the elite class, a gemstone must not only have a score of 95 points or higher, but also be free of obvious defects (category C). The Elite Ideal subclass must include only gemstones with a score of over 99 out of 100 and without any defects of categories B and C. Stones with a "window" must also be excluded from the elite class.

Why do we need such rigorous and highly accurate testing? Why not use the well-known GIA grading system (symmetry/proportion/cut quality)? Some might say, "In any case, the eye can't detect cut flaws visible only through a loupe, and it's also unclear why we need to calculate them." Let me start with that last question.
Once upon a time – 11 years ago, to be exact – I cut a stone for the American Cutters Guild competition. I showed the stone to a friend, and he asked me to cut the same stone for him. Okay, so I did. But since it was the second stone, it was cut a little more precisely: some facets were polished a little better, some mating points were a little more perfect… If I were to grade these stones today using my method, they would score about 97.5 and 99 points respectively. The difference is minimal, which means there are a whole bunch of commercial cuts even below 70 points. But… I deliberately showed both stones to many people – usually non-professionals, and, of course, without a magnifying glass. Almost all of them – almost all! – agreed that they liked the second stone more than the first, even though both stones are identical with microscopic deviations in accuracy – no more than 1 point out of 100! No one could explain why, they simply said they liked the second stone better – simply by feel.
This led me to a surprising discovery. Our eyes are perfect optical instruments, capable of perceiving the smallest details. However, to prevent overload with "unnecessary" information, our minds set a certain sensitivity threshold, beyond which these details are not recognized at the conscious level. But they reach another level—the subconscious—and evoke the aforementioned feelings. The fewer imperfections, the more harmonious the gemstone appears, because the sense of harmony and the pursuit of perfection are inherent in each of us.

There are many connoisseurs of beauty and perfection in the world. People are willing to pay enormous sums for works of art that convey emotions through the harmony and perfection of nature or the human body with incredible precision. Such connoisseurs are also found among gemstone lovers, although many still don't understand just how perfect gemstones can be. Our task—gemologists, appraisers, dealers, and cutters—is to express this perfection in numbers.

What do we see in the market today? It's claimed that the value of a gemstone is determined by the four "Cs": color, clarity, carat weight, and cut. But, in fact, the fourth "C" is currently ineffective. Almost no one (with the possible exception of the Spanish Gemological Institute) includes cut details on their certificates, only occasionally mentioning the shape—round, oval, cushion, and so on. But, firstly, a gemstone's shape isn't a determining factor in value. And secondly, the current cut grading system offers a rather vague understanding of precision. What are five grades, from poor to excellent, really? Each grade isn't a point, but an interval, and a huge interval at that, denoting a surprising variety of cuts. And "proportions" as a definition is difficult to use for colored stones, because the optimal shape depends on the jewelry design.
But thanks to advances in cutting equipment, more and more finely cut stones are appearing on the market. The difference in perfection between jewelry crafted with a microscope and gemstones cut with a 3-5x loupe is becoming smaller and smaller—at best.

There are emerging masters with experience in technical cutting competitions and knowledge of how precise a cut can truly be. And, most importantly, there are buyers who are beginning to ask "difficult" questions about cutting precision. These first harbingers of change don't yet signal the storm itself, just as the first drops of rain don't mean a downpour, but they do indicate one. And if we want to be prepared to answer these questions tomorrow—correctly and reasonably—then today we need a simple, reliable, and accurate tool for assessing the fourth "C"—cut quality. What seems exotic and eccentric today will become possible tomorrow, and the day after tomorrow, commonplace. Such is evolution. Such is history being made.