Article: The grading of diamonds: How to explain it in a simple and comprehensive way

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La classificazione dei diamanti: Come spiegarla in modo semplice ed esaustivo

Mar 23, 2022

The grading of diamonds: How to explain it in a simple and comprehensive way

Diamonds are a product of nature and for this reason they are subject to changing conditions that can affect their chemical composition and the presence of foreign elements, creating diamonds of different quality. A grading system has the purpose of ordering the quality of diamonds according to specific principles and based on it to establish a price.
The diamond grading system takes into consideration 4 aspects: carat, color, clarity and cut (the 4 Cs from the respective initials of the names in English).

Carat

Diamonds are weighed in metric carats which equals 0.2 grams or 0.007 ounces, and centesimal fractions (or points). The name carat derives from the seed of the carob plant which were used in ancient times to weigh the gems, because they were believed to have a very constant mass. For operators in the sector, it is easy to understand the size of a diamond by weight, but for buyers it is not at all. The following tables of the ratio of carat weight to dimensions may be useful for this purpose.

Clarity

The clarity indicates, according to certain degrees, the presence or absence of imperfections and inclusions in the diamond. Imperfections indicate all those characteristics that are on the surface such as scratches, abrasions, small notches etc. Inclusions are those characteristics that are found inside such as crystals of other minerals, breaks, distortions of the crystal, etc.

Among the imperfections and inclusions, it is the latter that has the most serious impact on the grade, value and beauty of a diamond. The degree of clarity is determined using a 10x magnification. At the top of the scale we find pure diamonds, with no defects or inclusions, extremely rare and therefore very expensive. At the opposite end of the scale, we find diamonds whose inclusions or imperfections are visible even to the naked eye. Between these two extremes are diamonds with inclusions ranging from very difficult to easily visible at 10x magnification. Here is a summary table of the degrees of clarity of the GIA (Gemological Institute of America):

FLAWLESS (FL): Diamond with no imperfections or inclusions.

INTERNALLY FLAWLESS (IF): Diamond with no internal inclusions but only a few minutes external characteristics.

VERY VERY SLIGHTLY INCLUDED (VVS1 / VVS2): Diamond with inclusions that are extremely difficult to see (VSS1) or very difficult to observe (VVS2).

VERY SLIGHTLY INCLUDED (VS1 / VS2): Diamonds with inclusions ranging from difficult (VS1) to slightly easier to see (VS2) are classified in this category.

SLIGHTLY INCLUDED (SI1 / SI2): Diamond whose inclusions are easily seen (SI1) or very easy to see at 10X magnification (SI2).

INCLUDED:

I1 - Diamond showing inclusions visible to the naked eye with moderate effects on beauty or durability.

I2 - Diamond showing inclusions visible to the naked eye with serious effects on beauty or durability.

I3 - Diamond showing inclusions visible to the naked eye with serious effects on beauty and durability.

Color

In nature, diamonds exist in many colors such as yellow, brown, green, pink, orange, purple, blue, called fancy diamonds, but the vast majority of diamonds

are almost colorless to light yellow or brown. Towards the end of the nineteenth century the most commonly used terms to describe the color of diamonds were based on the names of the mines from where they were extracted for example in South Africa, we find the term Jagers, from the name of the Jagersfontein mine, to describe colorless diamonds with blue fluorescence, the term river was used for colorless diamonds without fluorescence, as diamonds mined from alluvial deposits were believed to be mostly of this type. The terms Top Wesselton and Wesselton derive from the Wesselton mine to indicate almost colorless diamonds. During the twentieth century other color scales were created that used numbers (1,2, 3, etc.) or letters (AA, A, B, C, etc.) or terms such as Blue White, Fine White. Towards the end of 1950, the most used color classification scale in the diamond industry was that of the GIA (Gemological Institute of America). The reason for the affirmation of this scale lies in the long history of professional teaching and the wide dissemination of its Certificates of Qualitative Analysis of Diamonds that used this type of graduation scale. Over time, these terms have also become familiar to consumers.
GIA color grading scale:

Cut

The cut is a determining factor for the brilliance of a diamond and it is also the only factor in which human work and experience intervene. The cut can both mean the shape in which a gem is cut such as round, oval, drop, etc., and how it is cut, i.e. brilliant, step or mixed.

In the cut of a diamond or a gem, 3 distinct areas can be distinguished: where the facets are distributed:

In the brilliant cut the facets are in the shape of triangles and rhombuses. A round diamond has a total of 57 to 58 facets distributed as follows:

In the step cut the facets are in concentric rows of trapezoidal shape. The number of facets can vary according to the shape of the diamond. For example, the emerald cut has 58 facets: 25 on the crown, 25 on the pavilion and 8 on the belt. The number of facets in a rectangular cut is instead 30 facets.

Proportions

When ranking the quality of the cut, the most important factor is the proportions in the background, we find symmetry and polishing. Proportions are the relationships between the dimensions of its parts and the angles. The most important elements that are taken into consideration are:

Total depth
Table size
Crown angle
Pavilion angle
Girdle thickness
Culet size
Star facet length percentage
Lower girdle facet percentage

The cut of a diamond must be performed respecting precise proportions so that the light entering a diamond follows a precise path to return to the crown. In fact, we must imagine the pavilion as a mirror that receives the light from the crown and then returns to the latter, releasing all that sparkle of light that we observe when we look at a diamond. But to do this, the light must hit the facets of the pavilion with an upper angle of 24 ° 26 'called the "critical angle" (fig. 1). Now when the proportions are not precise (fig. 2 and 3), the light hits the pavilion at an angle lower than the critical angle, making the light scatter through the pavilion.

Symmetry

Symmetry is the equality between

the corresponding parts of a gem, this is important to create a balanced aspect of brilliance, fire and sparkle. For round diamonds, it was observed whether the facets are deformed or not pointed, if the table or the culet are off-center or not parallel or if the diamond is not perfectly circular, if the belt is wavy. For fancy cut diamonds, non-uniform angles or non-parallel sides, non-uniform lobes, non-uniform wings are also taken into consideration.

Finish

The execution of the design, the precision of the cut and the quality of the polishing are important factors for an optimal brilliance of the diamond. Above all, it reflects the skill and care that the cutter has been able to instill in the execution of the cut.

Cut grades

The GIA system of cut grades takes into account the individual elements of the cut (proportions, symmetry and finish), summarizing them all in one overall grade, which starts from excellent to poor.

Written by Stefano Montemurro