4C - HODNOCENÍ DIAMANTÚ

4C - Evaluation of diamonds

The main rules of 4C

Grading diamonds based on professional expertise, grew in response to the rapidly growing market for diamonds: the GIA (Gemmological Institute of America) established the Gem Trade Laboratory in the USA in 1935, the Gubelin laboratory in Lucerne issuing certificates since 1940, in 1961 the international organization, CIBJO was established to join producers and sellers of precious stones, jewels and pearls, and in 1976 the Dutch Department of Certification established the Diamond high council (Hoge Raad voor Diamanten - HRD). There are four basic parameters for evaluating and certifying diamonds:...

The main rules of 4C

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Cut

The modern brilliant cut is based on optical calculations focusing on maximizing the beauty of a diamond that comes as a result of its brilliance and dispersion. The brilliant cut has a round outline and consists of a crown (32 facets + table) and a pavilion (24 facets + a possible culet). Examination of the quality of a stone´s cut is based on comparing its ideal proportions with the symmetry of a mathematical model. Deviations from such a model are known as cut quality and are divided into several grades: Very good, good, fair, and poor. Some laboratories have the categories excellent or ideal...

Cut

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Color

The diamond is the only gemstone that occurs in all shades of color but the most common colors (after cutting) are from white to yellow. An international rating system from “D” to “Z” was developed for these basic colors. The whiter the shade of the stone, the closer the mark of the stone is to the beginning of the alphabet. Color specification must be performed by experienced professionals by using a set of sample stones and comparing them with a given stone. Carefully controlled lighting conditions must be used for example, normalized light of 5000/5500 K (D55) and a standard procedure...

Color

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Carat

The weight of a diamond is always given in carats and the international abbreviation, ct is used. The weight is indicated in certificates with 2 decimal places. Measurement is done with an accuracy of 3 decimal places. The second decimal place can only be rounded up if the third decimal place is 9. 1 ct = 200 mg = 0.2g According to the strict defined parameters of a brilliant cut, it is possible to count the weight also by measuring the basic proportions of a brilliant-cut diamond, e.g. with the diameter (at least two axes perpendicular to each other) and height. Estimated density [ct] = (girdle...

Carat

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Clarity

The clarity is given by the number of foreign substances included in the diamond. Such in-homogeneities may be internal in which case they are called inclusions (black “carbon“, white “ice“, cracks, etc.). They arise during particular phases of crystal formation. Further, defects may be of an external character (scratches, extra facets), which may be caused through cutting and polishing or defects that couldn´t be removed during processing. The size and the placing of these inclusions are key factors for the process of grading clarity. A standard diamond grading loupe of 10x magnification...

Clarity

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