|DIAMOND GRADING. (INTERNATIONAL EXPERIENCE)|
|The main parameters of diamond grading are represented by four “Ñ”:
Each of these four parameters affects the price of a diamond. Therefore, appraisal is impossible without careful grading. Working with diamonds, an expert successively carries out the following procedures.
Performing diamond grading, an expert fills in the worksheet (testing records) which usually contains the following data:
When the proportions of a stone are calculated, the average girdle diameter (or width for some fancy shapes) is taken as 100%. Some parameters of stone proportions are interrelated, for example:
For this reason, some grading systems eliminate the measurements of some parameters if these parameters can be derived from other data.
When the girdle thickness is estimated in percentage, it should be noted whether the narrowest or the widest parts of the girdle are measured.
Luminescence grading often involves only determination of luminescence intensity, while its color is not graded.
To establish the effect of all cut irregularities on the diamond price, some cut parameters are described with tolerance values. For instance, within the GIA grading system, symmetry and polish are graded as "excellent", "very good", "good", "fair", and "poor". Such grades are usually applied to fancy shapes, because the effect of the geometry and pattern of a stone on its fire and the perception of the specimen as a whole is little studied, and no common standards are used for fancy cut styles.