Diamond Grading Report
Today’s ‘5th C’ is the diamond grading report. ‘Certificates’ as such do not exist for diamonds since the labs issuing them eschew giving any guarantees. ‘Grading reports’ as they are rather called, at their very best communicate a neutral opinion based on unbiased evaluation principles where personal preferences do not affect the judgement of a stone. However due to human involvement throughout the grading process and continuous development of the grading process itself any results will remain at least slightly subjective. And despite human graders working to their best of knowledge and experience, mistakes do happen. Particularly ‘borderline’ grade stones are at risk of being incorrectly graded. To remove any doubts two grading reports from two independent reputable labs are sometimes requested, particularly for more important stones.
To be safe buyers should always opt for one of the internationally reputable labs. These include the Gemological Institute of America (GIA), the Hooge Rad voor Diamant (HRD), the International Gemmological Institute (IGI) and the American Gem Society (AGS). All aforementioned labs grade against a globally accepted standard. In-house ‘certificates’ on the other hand should always be strictly avoided.
GIA reports are overall the most highly regarded grading reports. The AGS, the oldest lab is also sound but remains little known. Reports issued by the HRD of Antwerp, Belgium, a name familiar accross Europe, and the International Gemmological Institute (IGI), also known to Asians, are well established alternatives. Whilst arguably a touch softer in terms of grading standards, particularly IGI reports are considered to be fairly consistent.
A layman should however never rely solely on a paper but rather consult a well versed diamantaire who can accurately interpret a report and assess a stone for what it truly is. Only diamond professionals possess the profound knowledge to compare the inherent qualities of a particular diamond against the dataset provided by a grading report. Furthermore certain qualitative factors will overrule others. Moreover particular stones as opposed to the best ‘paper stones’ can represent relative value-for-money. The global diamond wholesale market further tries to eliminate pricing inconsistencies by applying appropriate premiums or discounts respectively to stones according to their certificates. For example a GIA stone might be the best and most costly witin its class in absolute terms, however a certain HRD stone could be a relative bargain since it is still a good stone yet it’s price may be considerably lower. This is particularly true for non-investment stones below the 50k usd.
A grading report will always provide a summary of a the 4C’s of a stone covering carat weight, colour, clarity and fluorescence as well as overall cut grade. The cut of a diamond includes its proportions, symmetry, and polish which are always depicted. A report will contain the precise metrics of the diamond including important ratios in percentage as well as relevant angles expressed in degrees.
The grading report also incorporates an annotated proportion diagram which illustrates the cross-sectional profile besides a reference/plotting diagram. The latter is composed of a top and a bottom view which act as illustrative ‘maps’ showing external (blemishes etc.) and internal (inclusions etc.) features of the stone. Such features are plotted, if present, according to their true positions as external (in green) and internal (in red) features. Extra facets in black may also be shown.
Usually clarity characterists are also listed in the grading report, with the first one being grade-setting. If this is not the case the final clarity grade is derived from the totality of internal features present and the overall impact they may have on the particular stone.
The grading report for round and fancy shaped diamonds of the normal colour range (D-Z) will always be the single most important determinant of price.
Contrarily a natural fancy coloured diamond grading report represents more of an approximation since for example the colour descriptors mentioned may vary from the true colour. ‘Good paper’ stones are visually less pleasing than their report as opposed to ‘bad paper’ stones which are more beautiful than their actual grading report implies. The trade will always differentiate in such instances and pricing will usually reflect a more accurate integration of both these sets of information. Ideally a fancy coloured diamond will possess both an optimal certificate and a corresponding colour.
Factors such as cut, depending on the actual colour of the stone are also not given the same level of attention as is the case with colourless diamonds due to absolute rarity. Furthermore the actual color intensity described in a fancy colour diamond report merely represents a range within a certain saturation level. To accurately value a fancy coloured diamond the visual impact of both the tone and the intensity of the colour needs to be assessed. A report fails at this task. Although there is much scope for new grading labs to enter this specific domain, the currently only accepted natural fancy coloured diamond grading report is that of the GIA.