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              Classification : 4Cs of diamond quality



The value of a cut diamond is not random, it is based on internationally recognized standard system. It is the rule of graduation known as of the 4Cs: Carat - the weight; Colour - the colour; Clarity - purity; Cut - size. One uses these same criteria to evaluate the invaluable and fine stones, the whole of these criteria will allow to evaluate in terms of values, the stones in question according to codified methodologies'. It classification of categories of diamond (4Cs) is realized by professionals. One calls the people in charge of this work the gemmologists. The diamond cutter a contrario of the gemmologist does not study the invaluable stone but negotiates it.

The beauty of a diamond depends on these quality standards, but they are subjective criteria there. Visual attraction as for it is likely to vary from one person to another.

There are however several scales or models of classification: Gemological Institute off America (GIA) which founded in 1953, the classification of the diamonds based on the 4C, Confédération International of the Jewellery, Joaillerie, Orfèvrerie of Diamonds, Perles and Stones (CIBJO), American Gem Society (AGS), etc. , the concepts quoted in its various models are appreciably the same ones, all depends on the country (cultural).

The criteria gemmological which will be fundamental to allot a value (in terms of price) to the stone are: 

  • The weight
  • Clarity
  • Color
  • Cut: quality of symmetry and the polish
  • Fluorescence

These criteria are retranscribed on paper in the form of certificate, thus giving an identity card to the stone. The certification of cut diamonds is the best means of guaranteeing to the purchaser the authenticity and the quality of diamond in question. For the consumer it plays a part of confidence making it possible to sell diamonds throughout the world without having diamond under the eyes.

The three aspects of certification are, the identification, classification according to 4Cs, as well as the determination of the origin of the colour of fancy diamonds.

Gem Trade Laboratory (GIA Gem Trade Lab), in Carlsbad in California, one of the many departments of this institution, is specialized in the classification of diamond, it makes authority as regards certification of cut diamonds. This scale of classification for colourless diamonds extends from D which is completely deprived of colour, therefore colourless or almost to Z which is a yellow or brown pale colour. This system is recognized and used universally, the jewellers, gemmologists and diamond cutters use it with the daily newspaper.

                                         Weight / carats

According to the main lines of the CIBJO relating to the sale and the marketing of diamonds, the gems of colour and the pearls, the weight of diamonds is expressed in carats. It is the measuring unit recognized for the weight of the gemstones. An equal carat 0.2 gram as one gram represents 5 carats.

The carat is divided into hundred points or hundredth of carat. In the trade when one speaks about small diamonds one intends to speak about, 10 points (a tenth of carat), 25 items (1/4 of carat), 50 items (1/2 carat). For diamonds which weigh less than 0,20 ct, one speaks about fray, used in particular for diamond paving. Diamonds of a carat or more being much rarer, their relative prices per carat are high.

However, the commercial practice wants that one rounds the weight of a diamond at the point
superior, only when the third decimal is equal to 9, it is the international rule.

Examples :

For a diamond of 0,349, one will round to 0,35 carat
For a diamond of 0,147, one will round to 0,14 carat

One uses to weigh the weight of a diamond an electronic balance which has a precision with the thousandths of carat. Here an example of very precise electronic balances allowing to give 3 digits after the comma.


Below a charts for estimating the weight of diamonds use only as an indication.




                                                 Clarity

Clarity of a diamond makes reference bye the presence or absence of inclusions or imperfections internal or external of the stones, detected by an exerced eyes or with a loupe x10 magnification. It is given by considering the localization, the quantity, the size, the form, the colour of inclusions. It is established when diamond is examined by a gemmologist or of a binocular microscope. If a diamond show no inclusions he will recive the grade Flawless (FL) or Internally Flawless (IF) to him, it represent the perfect purity, of great rarity and highest quality.
Diamonds contain also a large variety of inclusions which can modify its appearance. The degree of purity of a diamond as proposed by the GIA is expressed as follows:  

  • Fl – Flawless
  • IF – Internally flawless
  • VVS1 et VVS2 – Very very slightly included
  • VS1 et VS2 – Very slightly included
  • SI1 et SI2 – Slightly included
  • I1, I2 et I3– included
According to CIBJO:

Grade
Signification
Loupe clean (LC)
No inclusions visible under a 10x magnification
VVS1-VVS2 (Very Very Small inclusions)
Minute inclusions visible under a 10x magnification
VS1-VS2 (Very Small inclusions)
Minor inclusions visible under a 10x magnification
SI1-SI2-SI3 (Small Inclusions)
Shall contain noticeable inclusions visible under a 10x magnification
I1-I2-I3 (Imperfect)
Shall contain inclusions visible under a 10x magnification

According to the type of the diamond certificate, there will contains a graphic representation of the external and internal characteristics. It consists in reproducing the inclusions and the surface characteristics which contribute to determine the grade of purity. This graphic representation is very useful because each diamond are alike, it' s them fingerprint. We uses internationally recognized symbols, the red corresponds to inclusions (nternal) and the green is used for the external characteristics.


                                                  Color

The colour of a diamond is very important, contrary to the purity it is distinguished more easily with a exerced eye. In the case colourless diamonds are diamond with no colour which is required, i.e. the colourless absolute. The colour range of diamond is expressed by a letter going from D to Z, D being a perfectly colourless diamond and Z a diamond having a slight hue of yellow, grey or brown. Below, we present  the scale for colour grading as well as a comperative chart of colour grades between the GIA and the CIBJO scales.

GIA / Grade
CIBJO / Couleur
D
Exceptional white +
E
Exceptional white
F
Rare white +
G
Rare white
H
White
I et J
Slightly tinted white
K et L
Tinted white
M à Z
Tinted

To determine the slight colour present in colourless diamonds, we used masterstones, especially calibrated by the GIA. This set of masterstones are selected according to several criteria.

 

The classification of the colour of colourless diamonds or almost is done by comparing the colour of the stone to be classified with that of the master stones by using a day light lamp. There are  especially designed to classify the colour of diamonds, the name is Diamondlite.

Brown diamonds darker than the grade K will be described by employing their category of letter and a descriptive expression. Diamonds between K and M are graduated with the weak expression brown, N with R is very light brown and S by Z is graduated light brown. Diamonds with more depth of colour than range Z will be classified in the category of fancy diamonds.



                                                   Cut


Cut beauty of a diamond is determining and it is responsible for the fire and the brillance of the stone. It is that of the four criteria which is appreciated most easily with the eyes,  but at the same time it is most difficult to analyze with precision. Diamond must be cut according the proportions', it is what we say "ideal proportions". Diamond has a very high dispersion. This dispersion is responsible for the subtle flashes of colours, which one calls “fires of diamond”.

Photo : The mecanism of dspersion in diamond 

 




                                           Fluorescence

A great majority of colourless diamonds present a reaction when one exposes them under a lamp to ultraviolet ray, one calls this phenomenon “luminescence”.

This luminescence or fluorescence can be of blue colour, white, to see even yellow or green, it forms whole part of the certificate, it is an additional mark of identity, a mention will be made on the describing certificate: its colour and its intensity.

For an absence of fluorescence: “none” or “inert”.
For a light presence of fluorescence: “slight” or “light”.
For an average presence of fluorescence: “medium” or “average”.
For a strong presence of fluorescence: “strong” or “strong” .

The impact of fluorescence on the price of a diamond depends on its effect on this one. If you notice that your diamond  are fluorescent  in particular in night club, do not think that it is a “false”.

 

 

 

Did you know ?
Before the 80's, the expression “crapaut” or “crapot”, was employed for designer natural inclusions present in a diamond. This expression is obsolete, rising generation of gemmologists forgot.


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