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5th C : Certification

Though the 4Cs are commonly used as guides in diamond purchase, only experts in gemology can really evaluate a diamond based on these 4 characteristics. In grading a diamond, gemologists use highly sophisticated spectrometers and other high-tech equipment. Independent gemological laboratories issue a document containing the vital characteristics and the grading of the 4Cs.

Certification is the 5th C of a diamond purchase. The certificate does not give the monetary value of the diamond; it conveys straightforward product information that fully describes and evaluates the critical factors about the gem that affect quality, beauty and value. Even diamond experts rely on certification to verify their purchases.

A certificate is also useful for identification purposes in the future. For example, in the case of a lost or stolen diamond, a certificate will facilitate its replacement with a diamond of equivalent quality.

Here's what to look for in a reliable diamond certificate:

Date of the report: It's possible that the diamond has been damaged since the report was issued. Ask your retailer to show how your diamond matches with the certificate offered.

Unique identification number: EGL USA offers consumers an easy on-line verification of their individual certificates. Very often the ID number will be laser inscribed on the diamond. If not, you can ask your jeweler to have it done. All certificate numbers issued by The EGL USA Group are preceded by either "US" or "CA," depending on whether it is issued in the U.S. or Canada.

Issuer of the report: Make sure that the issuer is an independent, well-established and respected laboratory. GIA is not affiliated with any retailer, wholesaler, or manufacturer, you gain extra peace of mind knowing that your GIA report represents the impartial opinion of unbiased professionals.

Shape and cut: Shape, such as round, pear or oval, and cutting style, such as brilliant or step cut, are noted on a certificate.

Measurements: Major laboratories measure diamonds in millimeters, typically to the hundredth of a millimeter. Exact dimensions are very important in identifying a diamond, as it is unlikely that two diamonds will have identical weight and dimensions.
Carat weight: An exact measurement must appear on the report.

Colour Grade: A grading which assesses the absence of colour in a diamond.

Clarity Grade: Clarity grade determined under 10x magnification.

Cut Grade: A grade of cut as determined by a diamond's face-up appearance, design and craftsmanship. A cut grade is available on round diamonds graded after Jan. 1, 2006.

Proportions: Good proportion--particularly the depth and table percentages--influences the brilliance and fire of a diamond. In fact, proportion is as important as color and clarity grades.

Finish: Grades that represent a diamond's surface and facet placement.

Polish: Rating the overall smoothness of the diamond's surface.

Symmetry: Measuring the shape, alignment and placement of the diamond's facets in relation to one another as well as the evenness of the outline.

Fluorescence: Colour, and strength of colour when diamond is viewed under UV light.

Comments: A description of additional diamond characteristics not already mentioned in the report.

Clarity Plot: A map of the approximate size, type, and position of inclusions as viewed under a microscope.

Proportion Diagram: A map of the diamond's actual proportions.

Reading a Proportion Diagram

Proportion diagrams will typically include the following information:

Depth: The height of a gemstone measured from the culet to the table.

Table: Located at the top of the diamond, the table is the largest facet of a diamond.

Girdle: Range of girdle thickness.

Culet: Appearance, or lack thereof, of the culet facet.

Take the time to understand how to read a certificate, however, your diamond purchase should not be based solely on this document. It cannot replace a visual inspection of the diamond you are considering. Some diamonds are beautiful even if they don't look good on paper.

Finally, remember that diamond certificates are not guarantees, valuations or appraisals. While professional labs employ experienced well-trained graders and use the most accurate gemological instruments to grade gemstones, laboratories make no warranties regarding the accuracy of their certificates. Diamond grading, like diamond cutting, is both an art and a science.

Carat Weight


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