They say that an important criterion for gemologists when evaluating a diamond is the cut of the stone. And they are right. Imagine that you are looking at two stones with the same characteristics – both VVS (Very Very Slightly Included), i.e. clean, almost without defects, very small inclusions can be seen only in a microscope. And the shape of the cut is the same. But one of them shines with stellar brilliance, mesmerizes and beckons, and the second one next to it looks like an unattractive poor relative, in which there is neither strength, nor play, nor brilliance, nor, to put it bluntly, special beauty. And it seems to be smaller in size than its luxurious counterpart.
What is the difference between the “twins”? It lies in the quality of cut, the notorious “ABVG” according to the Russian TU 117-4.2099-2002 and the 4th C (CUT) according to the international GIA system.
Cut quality
What is diamond cut quality and why is it so important? Nature creates a diamond, endowing it with magnificent characteristics that have yet to be seen and revealed. And the cutter acts as Pygmalion, extracting his shining Galatea from a seemingly insignificant white, translucent cobble.
It is not by chance that a facetter is the most respected profession in the jewelry business. Not every master is allowed to approach quality diamonds. And these royal stones will not be entrusted to him immediately, but only when the diamond cutter has at least 5 years of experience and thousands of carats of cut semi-precious stones.
A “diamond sculptor” creates a multifaceted prism out of a diamond, in every facet of which light reflects and shines. And it is the skill of the diamond cutter, his ability to reveal the diamond’s ability to reflect light rays, to play, to “burn”, that determines the attractiveness and beauty of the stone. The more skillful the cutter is, the more dazzling the diamond that comes out of his hands. And the higher the characteristics and value of the stone.
It should be noted that the quality of the cut and its shape are different categories. Any shape – oval, round, rectangular, pear-shaped and others – can have an arbitrary number of facets:
There are stones with 73, 86 and even 102 facets (facets). As a rule, in these cases we are talking about large diamonds weighing 1 carat or more.
Now that we have sorted out the terms, let’s move on to where we started – the systems for assessing cut quality.
Cut quality according to the Russian TU system
The quality of diamond cutting in our country is assessed according to the TU 117-4.2099-2002 system, which applies both to gems in jewelry and to individual stones not set in a setting. Depending on the cut characteristics, round diamonds are “enrolled” in one of 4 groups.
Types of diamond cut quality:
Diamonds with 17 facets or with some fancy cut shapes can be assigned only to groups “A” or “B”.
Fig 1. What are the parts of a Kr-57 cut diamond called?
According to the specifications, the cut is evaluated according to 5 parameters:
Each of these parameters must lie within a well-defined range.
Fig 2. Ideal proportions of a diamond
According to Marcel Tolkowsky, the ideal proportions of a diamond (calculated as a percentage of the diameter) are as follows:
These proportions, which make it possible to reveal all the “talents” of the stone, were calculated by a scientist-mathematician almost a century ago, and to this day are considered the standard. Of course, in practice it is not often possible to achieve such an exact ratio, so there are tolerances. For example, the girdle thickness is allowed up to 5 %, and the size of the pad can range from 53 to 65 %.
The Russian grading system is seriously different from the global GIA system. First of all, it is stricter – a diamond that has received the highest characteristic according to the GIA is often able to be awarded only the second group – “B” according to the Russian TU. This is due to the fact that the Russian system was developed for the production of gemstones, while the international system is used to assess their value.
GIA cut quality
The GIA system of comprehensive diamond grading (the 4C’s system) was developed in the United States around the middle of the last century and is considered more universal than the Russian TU. It considers the parameters of a stone, with the name of each stone beginning with C:
According to the GIA, the cut quality of a stone is evaluated on three parameters: Cut Grade, Polish and Symmetry.
Each parameter is rated on a 5-point scale:
A stone that has been awarded Excellent in all characteristics receives the Triple X “title”. In addition, in the GIA certificate you can see the line “fluorescence” (Fluorescence) – the glow of the stone in ultraviolet light. It also affects the value of the diamond.
The international and Russian systems for assessing the quality of a diamond cut do not overlap, as both were developed for different purposes. We wrote about this above.
Why the proportions of a stone are so important
The importance of a stone’s proportions cannot be overemphasized. It is their correct ratio that guarantees that bright shine, play, “fire” that mesmerizes us in a quality cut diamond. After all, a natural diamond is a rather unassuming thing, and only precise calculation and filigree skill of a person turn it into a symbol of beauty. What happens if a master starts cutting a stone as God would have it, without observing the proportions?
Fig 3. Reflection of light in a diamond
If the height of the stone is too high relative to its diameter, the gem will appear smaller and the center will appear darkened. This is due to the fact that the light from the bottom of the diamond is reflected at the wrong angle.
Well, if the height is insufficient, the stone will not refract light rays, but scatter them, which will make its shine less bright. Moreover, a flat stone can often have a fisheye effect. From the top of the stone, a dark dim ring will become clearly visible, resembling the extinguished eye of an aquatic inhabitant.
The rundist is that “girdle” of small facets at the junction of the crown and pavilion. It is this surface that serves to anchor the stone in the setting. If the width of the girdle is insufficient, it will make the edges of the diamond brittle. Everyone understands what this is fraught with. But too wide girdle is not good either. It makes the stone visually appear smaller, especially after it is placed in the setting.
Fig 4. Calette of a diamond
The calyx is where the diamond ends, the smallest facet at the bottom of the pavilion, parallel to the top. Ideally, if it is not present at all, or if it is vanishingly small (a spike). In the GIA certificate, this parameter is also present. Although the main purpose of the kaleta is to ensure the strength of the stone, aesthetics are also important. If you look at a gem with a large kaleta from above, it will look like a dark dot in the depths.
How symmetry affects a diamond
Symmetry is an important indicator of cut quality. If the facets of a gem are well lined up and perfectly positioned relative to each other, light from them will be reflected at clear angles and at maximum volume. A symmetrical stone truly shines.
An unsymmetrical diamond is a diamond that:
If the GIA grades the symmetry as Excellen or Good, the stone will look just perfect. But you should realize that a Good grade reduces the gem’s value by 10-15%. So, if your goal is a diamond for jewelry and not as an investment, you can save on symmetry.
The perfect cut of a diamond
And now for some romance, burning hearts and dagger-sharp arrows. However, speaking of the perfect diamond, you can’t do without it. Perhaps you know such a child’s fun – a kaleidoscope tube with an eyepiece and a handful of colored glasses inside a body lined with mirrors. Remember, what mesmerizing magic was created at every turn of the tube. An equally marvelous spectacle, but only static, can be seen in a well-cut diamond.
Fig 5. Hearts and arrows in a diamond
“Hearts and arrows” is an effect that occurs in a round-cut stone when it is looked at with a magnifying glass through special colored filters. If you look at the diamond from the side of the culet, you can see converging figures-“hearts”, and if you look from above, from the side of the pad, you can see “arrows” with sharp “tips”. This visual effect is due to the stone’s excellent symmetry and good cut. Nevertheless, the presence of “arrows and hearts” cannot be a guarantee of the highest quality of cut, since its main parameter is not symmetry, but correct proportions.
Why not all diamonds are perfect
Let’s return to our “twin” stones from the example at the very beginning of this article. Why didn’t the master cut them the same way? After all, such gems are trusted only to experienced cutters. Moreover, if the stone has some small defects, quality processing can correct them, which means that the gem will be more expensive. So why?
The main reason is economic. Even if a diamond is cut incorrectly but has an impressive weight, its cost will be higher than a gem with an excellent cut but smaller in mass. That is, if a jeweler has a large diamond, then, not being able to give it a correct cut without reducing its weight, the master will deliberately cut it with defects.
Fig 6. Cost-effective cutting
Another alternative is to saw the stone into two pieces and cut each one to the highest level. But the result is the same: a pair of perfect gems, even together, will cost less than one non-perfect gem. So, our unattractive “twin” was at first the rather large diamond that the jeweler did not want to reduce or divide.
How polishing affects a stone
And, finally, let’s talk about polishing. This is the most important stage in cutting a stone. Without it, the gem will not sparkle. What happens during polishing? The master uses a special tool – a movable metal wheel – to polish the facets of the stone, using diamond dust and oil as an abrasive. This is an extremely labor-intensive and time-consuming process – a facet can be polished for several hours. What if there are 57 or 86 of them? The cutter must be in complete control of the process, otherwise the luster and brilliance of the stone will suffer. If the facets are polished correctly and there are no white lines, abrasions or irregularities on them, then the diamond is rated Excellent or Good in the GIA system.
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