Understanding a Diamond Grading Report

A Diamond Grading Report documents the specific characteristics of a diamond. These reports are issued by the Gemological Institute of America (GIA), EGL, AGS and many others. GIA is among the most respected organizations in the diamond industry.

Anatomy of a Diamond Grading Report

Date: Please make sure the certificate is not very old. Usually a certificate, which is 2-3 years old, should be good. In the case of an old certificate, usually 4 – 5 years old, you should make sure there is no damage done to the stone. No matter how old the report is, or what the jeweller tells you, check for nicks, chips, abrasions (can be caused by storing the diamond with other diamonds). Look around the circumference of the diamond with a 10 power loupe (your jeweller should have on handy, if not, perhaps this is not the right person to deal with).

Report Number: This is very important in case you loose your certificate. The number assigned to the Diamond Grading Report is on file with the grading institution that produced the report. Additional copies can be requested for a nominal fee.Shape and Cutting Style: The diamond shape and cutting style, e.g. round brilliant, pear shape, oval, princess etc.

Measurements/Dimensions: Lists the diamond’s dimensions in millimeters. This part of the report has the measurements of the stone in millimeters to the hundredth of decimal. The measurements could be the highest diameter measurement and the lowest diameter measurements for a round. Fancy shapes have the length and the width.

Carat Weight: The weight of diamond listed to the nearest hundredth of a carat. e.g. 1.01carats.

Color Grade: A grading which assesses the absence of color in a diamond.

Clarity Grade: Clarity grade (number and placement of inclusions in the diamond) determined under 10x magnification.

Cut Grade: A grade of cut as determined by a diamond’s face-up appearance, design and craftsmanship and based on several factors such as visual appeal, facet arrangement, pavilion facet angles, girdle percentages, etc. A cut grade is available on round diamonds graded after Jan. 1, 2006.

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: Color, and strength of color when diamond is viewed under UV light. Avoid diamonds with yellow or strong blue fluorescence. They make the higher color grade diamonds look milky or oily. Fluorescent diamonds have a very blurred brilliance. In lower grade diamonds they add value as it makes the stone look whiter than what is actually is.

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. Proportions are usually mentioned in percentage or angles. The right percentage and angles result in an optimum balance of dispersion and brilliance. They consist of Table %: The table decides how much brilliance (white light) is reflected back to the eye. A majority of diamonds have their table percentage ranging from 53 % to 64 %.

Reading a Proportion Diagram

Proportion diagrams will typically include the following information:

Total Depth %: The height of a gemstone measured from the culet to the table. This is very important. A diamond with a high total depth % (more than 63%) could add weight to the stone but no beauty. On the other hand low total depth percentage will look bigger to the naked eye than its weight. In both cases the stone looks dark when looking straight through the table.

Table: The table is the largest facet of the diamond and considered the window. In round brilliants, the range of generally accepted table to overall diameter is 53% to 66%.In fancy shapes, the table diameter and other proportions are not scrutinized in the same way as in round brilliants.

Girdle: Range of girdle thickness. This is probably the most neglected part by the consumer and rarely mentioned by the jeweller. A thick girdle adds to the weight of the diamond without adding to the brilliance or fire of the stone. It also makes a diamond setter’s life miserable. On the other hand, a very thin girdle is susceptible to chipping and breaking. I have seen diamonds that look like 0.80cts. but actually weighed 1.01cts. The girdle was so thick, it added to the weight but the diamond had no fire.

Culet: Appearance, or lack thereof, of the culet facet. It is the bottom tip of the diamond. The culet is not visible unless it is large, very large or extremely large These should be avoided. However nowadays minimal amounts of diamonds have these. They are mainly seen in older cuts like European, old mine cut. I have seen mishandled diamonds where the culets are abraded or chipped because they rubbed against other diamonds. Also, if the diamond is pre-owned, the setter could have caused damage to the culet or girdle of the diamond.