In the middle of the last century, the Gemological Institute of America developed a system for evaluating diamonds, in which a set of criteria such as color, clarity, cut and carat weight (together known as 4C) determine the quality of the diamond. It is believed that the higher each of the components the rarer, and accordingly, the more expensive the mineral. But is it really so? Let’s investigate.
As with colored stones, insignificant differences in the color of a diamond to the untrained eye can cause a noticeable difference in price. There are not so many exceptional colorless diamonds. Most of them have a yellowish or brownish hue, which makes such rocks less desirable. In the laboratories of the Gemological Institute of America (GIA), the most authoritative diamond evaluator in the world, the color of the minerals is determined under controlled conditions, comparing to masterstones — the stones of various shades estimated by a scale from D to Z — from extremely colorless to specimens with a distinctly yellow, gray or a brown tinge. In addition, more than 50% of diamonds emit a light under ultraviolet radiation that is almost imperceptible to the human eye under normal conditions; this is called fluorescence, which is the result of a change in the molecular structure of a diamond. In diamonds with D-F colors (the first three scale marks), this glow effect is undesirable, and the more noticeable, the higher the discount at the sale (up to 45% of the Rapaport price list). At the same time, fluorescence can visually improve the characteristic of a stone with a cheaper shade and make it commercially more attractive — the fact is that most often it has a bluish shade in the ultraviolet, which gives the stone a more desirable visual appearance. This effect, on the contrary, may increase the price of such minerals.
The degree of a diamond’s purity is determined by the size, shape, position and number of internal inclusions that are noticeable with a tenfold magnification. Almost all diamonds have defects, which makes every stone unique and dissimilar to each other. It is the imperfections that help specialists to distinguish natural diamonds from counterfeits, and also to identify a separate mineral. In the GIA grading system, internally flawless diamonds belong to the FL (flawless) group — they are considered to be the rarest and most expensive. On the other end of the scale there are stones with inclusions (I group, i.e. «included»), which are easy to see with the naked eye. An important role in the evaluation of the mineral is played by the defects’ locations — on the side of the faceted stone they have less influence on its transparency than if positioned under the table, hence an exemplar with inclusions in the central part can be from 10 to 30% cheaper.
The correct cut is extremely important for a diamond, since it can «visually improve» the stone with mediocre characteristics and make it more beautiful — the correct proportions, symmetry and polishing increases its brilliance. The perfectly cut diamond dazzles with its play and reflects the light by every facet. But as with other precious stones, the cutter often tries to reduce the loss of raw material; thus the processed rock may look too dim and ugly, and also have «windows» in the pavilion, the light in which is not reflected, but disappears without a trace. In the face of the common misconception, some customers are looking for stones with a larger diameter and less carat weight with the idea that such diamonds look more expensive. Visually, such a stone seems larger than it really is, but because of the «broken» symmetry it will come off worse. If we talk about liquidity, the range of choice should be narrowed to stones with a color from D to H; purity, from FL to VS2; and the quality of polishing and symmetry, no lower than «very good». Such stones reveal the beauty of a cut diamond.
The carat weight and price are also closely interrelated. The bigger the mineral the more expensive it is per carat. However, in search of a better diamond, it is always more appropriate to sacrifice its mass than any other characteristic. And also it is worth remembering that if we took two stones of the same weight, color, purity and shape, but the cutting, polishing and symmetry of the first one were excellent with a lack of fluorescence, while the second one were just good and emitted a very strong blue glow, the difference in their prices could be from 15% to 60%.