Color grading of lab grown diamonds
Having considered the main mechanisms for the formation of fancy colors of laboratory-grown diamonds, we smoothly move on to how to correctly characterize the color of such a stone, because the color of a diamond is the key factor that most strongly affects its value. In assessing the color of synthetic diamonds, as well as in the mechanisms of color appearance, one cannot get away from their natural counterparts. The color grading of any diamond is predominantly made according to the GIA systems developed for natural stones. But this is good, there is no need to come up with new classification systems, assessment tables - everything is ready, you just need to adapt a little to the specifics of the grown diamonds. Color is a subjective characteristic visually determined by the human eye and located in the visible range of the electromagnetic spectrum. A particular color is determined by the wavelength of the observed radiation. There are three characteristics for describing color: hue, lightness, and saturation. The term "fancy" means a rare or attractive intense color, used to describe the combined effect of hue and saturation.
How do I correctly assess the color of a diamond?
Evaluation of colorless diamonds in gemological practice is carried out under a D 65 lamp with a color temperature of 6500 K, on a white paper tray and using standards. The diamond is positioned spike upwards at a 45o angle of view (in the case of LGD, sometimes they look through the platform too), to the left and to the right of it, two reference stones that are closest in color are placed. Also, gemologists sometimes use a colorimeter - a device designed to determine the color (D-L) of a diamond by measuring the values of absorption and transmission in the visible part of the electromagnetic radiation spectrum.
Fantasy colors of diamonds are evaluated under all the same conditions as colorless ones, but with the platform up. For a rigorous assessment, the laboratory uses a viewing cabinet - a spacious chamber of about 0.5 m3 with special lighting and walls in a neutral color.
Now, instrumental methods for assessing color with computer data processing are also being developed - this is an analysis of the absorption spectra of diamonds in the visible region, the selection of corners that emphasize the color as much as possible for cutting a stone, an analysis of the resulting color by the coordinates of the color space. Because fancy diamond colors are unique and have an incredible range of shades, they cannot be compiled as a compact set of reference stones. Therefore, Munsell's atlas of colors is used as color standards - a book with pages in the form of plastic sheets with cells in which colored color swatches are inserted. Each sample in this atlas has its own coordinates in terms of hue, lightness and saturation. For example, a sample chip with coordinates 5Y7 / 4 will have a description for a hue of 5Y (yellow), lightness 7 (light), and saturation / 4 (negligible). The comparison method is used to select a chip sample that is as close as possible in color to the diamond under study. The GIA system adapted Munsell's atlas to its requirements in diamond grading, resulting in 27 color tone names and about 9 lightness and saturation groups.
(J.M. King, GIA colored diamonds, color reference charts)
The color gradation of laboratory-grown diamonds in terms of lightness and saturation (i.e., according to the degree of fantasy) generally consists of the following groups and in the following sequence: a number of colorless (DZ), then a gradual increase in one or another color in terms of tone and saturation - the Faint, Very Light and Light, then fancy colors - Fancy (Light, Intense, Vivid, Deep, Dark). After this description, the name of the color tone is substituted, for example, Fancy Light Blue. Sometimes there is an additional shade, it is placed in the name before the main color (for example, fancy intense purplish pink).
The cost of laboratory-grown fancy color diamonds.
In the laboratory-grown diamond market, there is no price gap between colored and colorless diamonds that exists in natural stones. Quite often, a premium to a lab-grown colored diamond is placed relative to the same (by weight and shape) diamond of color D (for example, a cushion 3.05 ct Fancy Vivid Blue diamond may have a 20-30% premium to the value of the price of the same diamond of color D). The complexity and cost of production of colorless, yellow, blue LGDs are almost the same, therefore their price cannot differ by much. Pink is a little more complicated, because the price of irradiation and annealing of this stone (about $ 100 / ct) is added to the price of a yellow diamond.
The most expensive group is Fancy - stones with a distinct fantasy color throughout the entire volume of the stone. The most expensive positions among the Fancy group are Intense and Vivid, for such stones a more significant premium to the cost can go (you need not only to grow a colored crystal, but also to correctly cut it, emphasize the color). The most attractive and trendy colors among LGD are pink, yellow, blue. Colorless stones are always in trend, they are classics.
Colors with prefixes Faint, Light and Dark are not attractive to buyers, therefore the cost of diamonds of this color is lower than colorless (D-F) and it is more difficult to sell such stones. For example, colorless stones with a very weak Faint Blue color are sold either at a higher discount, or at the price of low colors of the colorless range. The variation in shades of natural diamonds is wider than that of synthetic stones. This is due to the fact that each natural stone contains a unique inimitable set of admixtures, sealed in its structure, like DNA. And in laboratory-grown diamonds, we can control the concentration of impurities and, accordingly, the color.
This is much more convenient for the jewelry market - you can easily pick up a necklace with perfectly color-calibrated fancy diamonds.
Thus, the assessment of fancy colors of laboratory-grown diamonds requires additional equipment and the qualifications of a gemologist, however, reproducible colors are often found on laboratory-grown diamonds and this simplifies the work.
For a complete description of the color, you need to correctly determine the tone and degree of fantasy of the stone (lightness + saturation). The cost of the best colored LGDs is higher than colorless (D-F), but not significantly (not several orders of magnitude higher). Pink, canary and blue remain the most sought-after colors on the market. LGD color has a significant impact on the visual characteristics of the jewelry and the aesthetics of its perception.
Author: LGDeal Gemology Department