The International Diamond Council (IDC) recommends for the first time in its suggestions for a nomenclature in 1977, that in future all external defects should be included in the clarity grading, and has kept to this recommendation up to now. Excepted are loupe clean diamonds, in the case of which large external faults and definite structural distortions should be mentioned under "remarks", but not evaluated.
The size of inclusions is measured in microns. The diamond is termed "loupe clean" if it does not show any inclusions larger than five micron with 10 x magnification. To establish these limits a series of test brilliants with inclusions varying in size from two to fourteen microns was shown to diamond dealers and experts who tested the clarity under a 10 x magnifying loupe. The inclusions were studied solely with a loupe and not under a microscope.
The test yielded the following results:
Inclusions of the size five microns and under were not recognised by
anybody. Light-colored inclusions between six and seven micron were
only recognised by a few graders.
Inclusions of eight microns and over were seen by every test grader.
Based on these results the limit between loupe clean and VVS was set at an inclusion size of five microns. In the "IDC-Rules For Grading Polished Diamonds" of 1980 the definition for a loupe clean diamond is as follows:
"A diamond is loupe clean if it does not contain any internal faults which are larger than a dot-shaped inclusion of five micron viewed with good light contrast". In border-line cases the 1 Ox loupe is decisive.
Not only the number and size of inclusions are of importance when grading, but also their color, their position in the diamond and the number of facets through which the inclusion can be seen. A table which takes these factors into consideration is to be consulted to find the correct clarity grade. Other factors, apart from the ones mentioned, influencing the clarity grade are transparency, structural faults (for instance graining) and external features faults (for instance nicks, polishing marks or naturals). These irregularities have to be considered if they are easily discernable because of their color or reflecting properties or if the diamond has additional inclusions. On a certificate of a diamond graded as loupe-clean any irregular feature must be mentioned under "identification marks" or "comments".
It should be pointed out that the term "loupe clean" is to be preferred to the previously common designations of "clean" or "internally flawless". This nomenclature is logical, as diamonds are never entirely free from inclusions, and it is only a question of the magnification used whether they can be discerned or not.
In the practice of clarity grading, there are, of course, borderline cases in which inclusions of less than five microns must be graded as VVS, as not only brightness or reflectivity but also size are crucial in discerning inclusions. For if a highly reflective inclusion of less than five microns is located in a highly visible position, for example, just under the table, it can certainly nevertheless be seen under 10 x magnification, while the same inclusion in a less visible or well-lit position in the diamond remains invisible.
A crystalline inclusion looks quite different from a cloudy inclusion of the same size. How, for example, can a foggy cloud be measured, in which each particle is less than five micron? Longish inclusions have different lengths in different directions. Ultimately it is always the degree of discernibility which is decisive, and this cannot be registered by measuring techniques. Moreover nothing is said about the kind of light source to be used or its intensity. Far from decreasing, the sources of error could increase.
The varying importance attached to external defects in loupe clean brilliants as opposed to those in inclusions seems illogical and is not in accordance with international usage.
| GIA | Definitions of Clarity Grades according to Internal Defects in Accordance with the IDC |