Principle 4C in diamond valuation
GIA Color Evaluation of Diamonds
All diamonds can be divided into two groups by color: the first - from colorless to yellow -cape and the second - fancy-colored diamonds. To determine the exact color of the cape group diamonds, there are sets of color standards, for example, the most famous GIA scale of standards (from D to Z).
Other recognized international diamond grading systems use verbal descriptions rather than alphabetic designations when describing and evaluating color. Often, a certificate issued by one system contains a table of translations into the terms of another system's color.
Diamond clarity assessment by GIA system
As with the color estimation, all diamonds are placed on the "defect-free - defective" scale when determining the purity group. At the same time, if internal inclusions are visible only in the microscope, but not in the magnifying glass with 10x magnification, the diamond is considered to be pure (defect-free). Five factors are taken into account when estimating the purity: size, quantity, position, nature and color of inclusions.
Evaluation of the quality of diamond cutting using the GIA systemCut quality is a composite parameter. It is defined as the aggregate of observing the proportions and symmetry of diamond elements and the quality of facet polishing. The influence of the quality of the cut on the cost is great, because diamonds with different cut quality look completely different. Regardless of the quality of the raw material, the quality of the cut can both lower and increase the cost of the finished diamond. The degree of influence on the cost of certain proportions, deviations in symmetry or defects in polishing is always a difficult question. Therefore, price lists do not contain tables that clearly indicate discounts or markups for the quality of cut. A stone can have proportions that will please one buyer and push away the other. That is why we can say that the quality of the cut is a speculative parameter that allows market professionals to buy cheaper and sell more expensive.
Jewelers have been experimenting with diamond cutting forms for a long time. In 1919, Marcel Tolkowsky proposed the angles for the facets of a round diamond, the most advantageous in terms of the diamond producing the greatest sparkle and colorful game. The proportions of the "ideal diamond" according to M. Tolkowsky (% of the diameter of the stone) are as follows: the site (Fig. Diamond Elements) - 53%, the total height of the stone - 60%, the height of the crown - 16.2%, the angle of inclination of the coronal edges - 34.5 °., the height of the pavilion - 43.1%, the angle of inclination of the pavilion edges - 40.75 °., the thickness of the girdle - 0.7% Diamond features, various specific tasks faced by the diamond cutter, often selfish goals of increasing the weight of the diamond due to distortion of the reference shape of the diamond lead to the fact that in practice there are always deviations from these values, although diamond cutters try to get into certain tolerances in terms of proportions when processing the diamond. They try to keep the pavilion's edges close to the ideal angle of inclination (41°), as the full internal reflection of the diamond depends on it. For example, the size of the site can vary from 55% to 65%, the thickness of the girdle can be up to 5%, the angle of inclination of the facets of the crown varies from 30 ° to 40 °. The play of light is also strongly influenced by the plane of the facets, the thoroughness of their polishing, the sharpness of the edges, symmetry (i.e., it is desirable that deviations from the norm were in "one way") and many other technological factors that depend on the level of technology of cutting production.
The practice of cutting has led to the fact that there are about two dozen forms of cutting, which can be divided into two groups: classical - a round and fantasy forms (up to one-off, individual) cutting. The classical form of cutting is conservative and is used for expensive diamonds, when diamonds are not only a jewelry piece, but also a means of capital investment (unlike fantasy forms, they give the maximum play to a diamond and are not subject to fashion trends).
Fantasy cut forms are used, on the one hand, to increase current trend demand, on the other hand, to increase the weight or other characteristics of the resulting diamond. Almost always, all other things being equal, a round-cut diamond is more expensive than a fancy-cut diamond. The existing diamond price lists provide for reference discounts on the price of round diamonds for common fancy cut diamonds.