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Diamond grading is the valuation, rating and categorisation of given features of a diamond in grades, according to internationally valid and approved rules and criteria.What is the purpose of diamond grading?

Grading of diamonds serves the possibility of valuation, comparability, and, ultimately, pricing.

What is the price of an economic good based on?

In history, only the rarity value of a diamond was decisive for its price. But with the discovery of diamonds in Brazil, or South Africa, at the latest, and with the attendant rise in world diamond production, this deteriorated rapidly. The rising production quantities meant a general rarity loss of the diamond, the loss of the hitherto paramount gem quality. It was replaced by a technique which identified the individual rarity (in contrast to general rarity). These individual rarity features were clarity and colour. To the development of the craftsmanship of the diamond cutter was added the assessment of the cut. And the fourth criterion had always been size, the weight of a diamond. Thus diamond grading rates a diamond according to its colour, purity, its cut and its weight. By means of these four distinctive features of equal rank the value of diamonds then can be determined and these made comparable among themselves (by price).

The difference between colourless and coloured diamonds, among other things, is that, with colourless diamonds, purity plays a very important role; in the case of coloured diamonds, however, intensity and attractiveness of the colour are more decisive than purity. Weight has long been stated in carats. Thus we get the famous 4 Cs which together form the basis for judging the value of diamonds. Colour Clarity Cut CaratColour GradingDistinction is made between so-called colourless and coloured diamonds.The hues are called "fancy colours" They mostly occur in weak saturation, they are pale . Almost every colour of the rainbow occurs: from red via orange, yellow, green to blue and violet.; there are also colour mixtures (brown) .These fancy colours occur rarely, which is why collector's prices exceeding even those of rare colourless diamonds are paid for such stones. This is especially true if the colours happen to be rich.Such colours are red, blue, purple, green and yellow or colour mixtures, e. g., greenish yellow.Diamonds termed "colourless" or "white" all show more or less visible colour saturation. In fact, this saturation is so weak that it will appear colourless to lay people. The trained, experienced eye is nevertheless capable of perceiving these differences in a direct comparison .The first internationally recognised definition for the classification of the colours was the so-called "yellow grading scale" also known as "Old Terms". Here the hues were given names according to the then most frequent occurrence in the respective colour saturation. The German counterpart for this was the RAL 560 A5E. In the meantime there have appeared improved guidelines of various institutes: by CIBJO, IDC and the Gemological Institute of America (GIA). Table 1 below lists the characteristics for the colour grading from the various organisations.For grading, the stone to be appraised is viewed and valued against standardised other diamonds under artificial white light. Artificial white light ("diamond light") is important because natural daylight fluctuates.

Clarity Grading:

All judging of the clarity of a diamond is made with a hand-held 10x magnifying glass (diamond loupe). This must be aplanatic and achromatic (no marginal distortions and no colour contours). Inclusions detected by a still greater magnification are not graded.As inclusions are deemed all naturally occurring and foreign substances, which may be solid, liquid or gaseous. In addition, these include cracks , structural properties and twin lamellas, etc..The internationally recognised grades are shown in Table 2.

Cut Grading:

Before the skill of diamond cutting was developed, the natural crystal form of an octohedron was the pre-eminent quality feature of the diamond. Hence a diamond with ideally shaped crystal form (geometrically-symmetrically perfect) was very highly esteemed.This criterion judges the outward characteristics and the proportions. The outward characteristics include natural and processing-driven characteristics and damage. Within the category of proportions are judged angle and percentage relationships between individual facet types , symmetry relationships, as well as polish (lustre) , see drawing with respect to proportions of a brilliant cut. The grades are listed in Table 3.

Weight (carats, cts):

1 ct = 200 mg (0.2 g). Weight unit in the gem trade since antiquity. The name is either derived from a seed ("Kuara") of the African coral tree or from a kernel (gr. "keration") of the carob tree.Subdivision in fractional (1/10 ct) or decimal numbers (1.25 ct). Very small diamonds are weighed by "points"; 1 point equals 1/100 Karat (0.01 ct)). The per-carat-price increases progressively with size, meaning that, with a price of DM 1000 for a one-carat stone, a two-carat stone would cost not DM 2000 but possibly as much as DM 3,500 .

The precise weight of a diamond can only be determined by weighing. Approximate calculation of the weight is possible with the aid of the Scharffenberg coefficient (S ~= 0,0067): d² x h x S (diameter d and height h).Until the beginning of the 20th century there still existed different carat standards (Florence C., Leipzig C., Paris C. etc.), which may result in discrepancies in the stated carat weight of historical stones The carat weight in the gem trade should not be confused with the carats stated for gold. Here carat is a term of quality : the higher the carat number, the more fine gold the piece of jewellery will contain (24 carats signifies 100% fine gold).The Grading ReportsWhat use are the above-explained values for the customer then?They are decisive. For the (reputable) dealers care about enlightening the customers and not leaving them in the dark about diamonds. That is why each diamond comes with a so-called "diamond grading report" or "certificate".NEVER buy a stone WITHOUT such a document !For safety reasons we sell our customers diamonds which are examined by one of the three internationally recognised institutes and sealed upon request. As soon as the customer is in possession of the diamond, he can of course open the seal.

The certifying institutes mentioned above:

HRD (Hoge Raad voor Diamant - Diamond High Council, Antwerp , Belgium),
IGI (International Gemological Institute, Antwerp, Belgium or New York, USA)
orGIA (Gemological Institute of America, New York, USA)

A diamond in a blister pack from HRD - the black rectangle on the right is the diamond grading report on microfilm. A diamond in a blister pack of the IGI - the black rectangle in the middle is the diamond grading report on microfilm.