By Dan Robinson, managing director of The Diamond Shop
The diamond certificate is an extremely important document, which is a blueprint of your diamond’s attributes and quality. It is issued by an independent professional gemological laboratory who measure, examine, and test your loose diamond under laboratory conditions. The certificate confirms a diamond’s legitimacy and unique characteristics and will give you peace of mind for the quality of your diamond.
In order to help you understand the diamond certificate, I will explain the different terms using a GIA (Gemological Institute of America) certificate as an example. The GIA are one of the world’s leading diamond grading laboratories. They issue a Diamond Grading Report which assesses the 4 C's of Colour, Clarity, Cut and Carat Weight, and includes a plotted diagram of the clarity characteristics as well as graphic representation of the diamond’s proportions. A Diamond Grading Dossier is a more compact version of the Diamond Grading Report, for diamonds generally less than one carat and does not include a plotted diagram of the diamond’s inclusions.
GIA Diamond Grading Report
The left-hand section of the diamond certificate has the following information:
Date: When diamond was examined.
Report Number: The individual number for the diamond, which can also be verified on the GIA website.
Shape and Cutting Style: Describes the shape, outline, and cutting style, e.g. Round Brilliant.
Measurements: Diamond dimensions in millimetres. A round diamond has two measurements for its diameter: minimum and maximum (e.g. 6.41—6.43mm) and a depth measurement (e.g. 3.97mm). All other diamond shapes are measured as length x width x depth.
Grading Results
Carat Weight: Diamond weight to the nearest hundredth of a carat.
Colour Grade: Diamond colour (from D to Z).
Clarity Grade: Diamond clarity (from Flawless to Included). Graded by the size, type, location and number of internal inclusions and external blemishes of the diamond.
Cut Grade: For Round Brilliant diamonds only. This indicates the quality of the cut, graded from Excellent to Poor.
Additional Grading Information
Polish: The surface condition of the diamond facets, graded from Excellent to Poor.
Symmetry: The symmetry and arrangement of the diamond facets graded from Excellent to Poor.
Fluorescence: A measure of visible light that some diamonds emit when exposed to ultraviolet light. This ranges from None to Very Strong.
Inscription: A laser inscription on the girdle of the diamond (usually the GIA report number) that can be used to identify it. Not all diamonds are laser inscribed.
Comments: Any extra identifying diamond characteristics.
The middle section of the diamond certificate has the following information:
Proportions
The top diagram shows the profile of the diamond, indicating its specific measurements, facet angles, and shape.
Total Depth: How deep the diamond is in relation to the diameter. Total depth % = (total depth ÷ average diameter) x 100. (e.g. 3.97/6.42x100=61.8%).
Table Size: The average table size in relation to the average diameter of the diamond. Table % = (average table size ÷ average diameter) x 100. (e.g. 58%)
Crown Angle: The average of all eight crown angles. A crown angle is the angle of the bezel facet plane relative to the table plane. (e.g. 35.5%)
Crown Height: The average crown height relative to the average diameter. Crown height is measured from the table plane to the intersection of the bezel facet with the girdle. Crown height % = (average crown height ÷ average diameter) x 100. (e.g. 15.0%)
Pavilion Angle: The average of all eight pavilion angles. A pavilion angle is the angle of the main facet plane relative to the table plane. (e.g. 41.0%)
Pavilion Depth: The average pavilion depth relative to the average diameter. Pavilion depth is measured from the culet to the intersection of the pavilion main facet with the girdle. Pavilion depth % = (average pavilion depth ÷ average diameter) x 100. (43.5%)
Girdle Thickness: The girdle of a diamond is the dividing line between the crown (top part of diamond) and the pavilion (bottom part of diamond). Girdle thickness and type (faceted or not) are described. (e.g. medium-slightly thick (faceted)).
Culet Size: The culet, when present, is the facet on the pointy bottom part of the diamond which helps prevent chipping. ‘None’ is used when there is no culet facet.
Clarity Characteristics
Plotting Diagram: An approximate diagram of the upper and lower halves of the diamond is shown. Various coloured symbols on the diagram show the location, type, and approximate size of the clarity features, which are diamond inclusions (internal) and blemishes (external). This diagram is a representation of the diamond’s fingerprint, as no two diamonds share the exact same pattern of these clarity characteristics.
Key to Symbols: This lists the symbols used in the plotting diagram, which correspond to the types of inclusions and blemishes in the diamond. (e.g. Crystal, Cloud, Feather, etc.)
The right-hand section of the diamond certificate has the following information:
Grading Scales
This is a diagram of the entire scales (Colour, Clarity and Cut) used for diamond grading, to give you a clearer understanding of your diamond's grade.
Security Features: These ensure the authenticity of the report and include a hologram, security screen and micro-print lines. Verification of the document can be confirmed by scanning the QR code which takes you to the GIA website.
Which Diamond Certificate?
There are many international gemological laboratories that issue diamond certificates. Different grading labs have their own diamond grading standards and techniques, which can result in very slight grading differences.
The Diamond Shop recommends the GIA (Gemological Institute of America) and AGS (American Gem Society). These grading laboratories are highly regarded and independent of any diamond retailers or wholesalers, so they offer you an objective and unbiased assessment of your diamond.
It is important to note that your diamond certificate is a diamond evaluation and not a diamond valuation. A valuation specifies a monetary value to a diamond, which is determined by fluctuating market conditions.
The Diamond Shop provides a GIA or AGS certificate and an insurance valuation with every diamond sold on our website.
If you have any questions, or would like more information on diamond certificates, just ask! service@thediamondshop.co.nz