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The smart consumer's diamond buying guide.... |
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Diamond Buying Made Easier > Diamond Grading ReportsDiamond Grading ReportsDiamond grading reports have become an essential element in how to buy diamonds. A diamond grading report will protect everyone involved in the sale of the diamond. Usually a diamond grading report is obtained by the diamond cutter or the diamond dealer after the diamond has been cut and the grading report will follow the diamond as it moves through the distribution channel.  Diamond grading reports are always
going through changes as the diamond market changes. At the time of this writing, AGSL (American Gem Society's grading lab) is announcing their newest product, a grading report for Oval Shape diamonds
that will include a diamond Cut grade. A few years ago, they started issuing diamond grading reports with diamond Cut grades for Round Brilliant Cut, Emerald Cut, and Princess Cut diamonds.
Having a Cut grade on these reports is a great thing as it helps to level the playing field for the consumer. These diamond Cut grades are a measurement of the diamond's optical performance that is determined by placing the loose diamond into a machine. It's not someone's opinion... it is something that is standardized so that is a good thing! Many many years ago, last century actually, I was in a jewelry store in New Orleans and I was talking to a young man that was the owner's son. After a little bit, his father showed up and he found out that I had previously worked for GIA, well the father began to give me his big long list of how GIA had ruined the jewelry business by teaching about Gemology and issuing diamond grading reports. I guess some people handle change well and others do not. The Elements of a Diamond Grading Report..... Even though diamond grading reports will continue to evolve there will still be some basics that should remain constant- > Diamond Grading Report Number- The world revolves around numbers! It is possible to go to the lab's website and check the report's validity and see additional information that might not be listed on the diamond grading report. Also this number may or may not be laser inscribed on the girdle of the diamond. Someone along the distribution chain decided to send the diamond to a certain laboratory and they also opted to purchase a certain type of report, the labs offer various types of reports. > Diamond Shape and Diamond Faceting Style- Diamond Shapes refers to the outline of the diamond.... Round Brilliant Cut, Pear Shape, Heart Shape, etc. Faceting (Cutting) Style refers to the facet style.... Brilliant, Step, or Mixed Faceting Style. > Measurement- Listed to the hundredth of a millimeter. Round Brilliant Cut diamonds- "minimum to maximum diameter x depth". Fancy shape diamonds- "length x width x depth". > Diamond Carat Weight- Must display diamond carat weight out to the hundredth of a carat, some diamond grading reports show carat weight out to the thousandth of a carat. Because the labs will only grade loose diamonds, they just throw it on the scale. > Diamond Color- Assigned a full diamond color grade, you will never see "diamond color grade ranges", G-H, I-J-K, etc. A diamond color grade range is only seen on appraisals for mounted stones. > Diamond Clarity- The labs use a system of having several people each calling the diamond clarity grade .... a system of checks and balances along with a dose of CYA. Diamond Proportions..... The following diagram is a very "well cut" diamond and it's proportions. On diamond grading reports you will see percentages for the table, crown, pavilion, and total depth. These are percentages in relation to the 100% figure, which is the diameter of the diamond (average diameter for round brilliant cuts and the width for fancy shape diamonds). Also listed are 2 important angles, the crown angle, 34.5 degrees, and the pavilion, 40.75 degrees.
> Table- The largest facet on a diamond. Mostly responsible for the amount of white light returning out of the top of the diamond. The quality and quantity of this white light coming up through the table is also called the brightness or brilliance of a diamond. The crown  (the angled facets between the table and the girdle) is mainly responsible for the breaking up of the white light that is returning up from the pavilion into its spectral
colors, this is called fire or dispersion. Just like you would see as white light passes through a prism (in the picture). As you make the table larger it will reduce the crown area and therefore
it will increase the amount of "brightness" and decrease the amount of "fire" in that diamond. It can be a matter of preference... I like tables to be less than 56% (giving it a larger crown area, so a bit more "fire") and some people like the look when the table is 60% or higher.> Crown- The crown is an angle and a percentage. The crown facet angle should be set to about 34.5 degrees.... if this angle starts to become shallower than 32 degrees there is a decrease in fire and an increased chance of durability problems. The crown height percentage is the area from the top of the girdle to the table. A 53% table with 34.5 degree crown will give you a 16.2% crown height. As the table percentage becomes larger or the crown angle becomes shallower, the crown height percentage will become less. > Girdle- The girdle should be thick enough to protect the diamond, period! If it any thicker than that it is just adding excessive weight and if it is thinner it can present durability problems. Normally a girdle that is in the range of Thin to Medium to Slightly Thick is acceptable. Sometimes it may be polished or faceted. > Pavilion- As with the crown, the pavilion has an angle and is also a percentage. The pavilion angle is very critical!.... if there is a variation from 40.75 degrees it will drastically affect the light performance of the diamond. The pavilion must act like a mirror. The pavilion height percentage is the area from the bottom of the girdle to the culet. > Total Depth Pecentage- The measurement from the top to the bottom of the diamond (depth) as compared to the average diameter. For example.... 4.04mm depth divided by 6.50mm average diameter= 0.6215 times 100 = 62.2% total depth percentage.  As shown above, the total depth percentage can be deceptive because it is the grand total of the crown height percentage, the girdle thickness, and the pavilion depth percentage. Two diamonds could have exactly the same total depth percentage but the three seperate sections of each diamond could be very different. > Culet- It may or may not be present. It is a facet placed on the bottom of the diamond for protection. As the diamond is being handled.... without the culet, the point at the end of the pavilion could easily be chipped in normal handling, such as being measured or picked up with a diamond tweezers. > Finish- A term referring to the overall combination of the polish and the symmetry grades. This is a comment on the care and skill of the diamond cutter used in cutting a diamond-  - Polish- These are minute surfaces items that are not part of the diamond Clarity grade. For example, polishing lines, scratches, nicks, pits, etc. - Symmetry- This refers to how the facets have been placed on the diamond and how precisely the facets are shaped and aligned to the top and bottom of the diamond. The reason for some of these symmetry variations was either for weight retention or an inclusion being cut away during the cutting process. Some of them just demonstrate poor cutting skills. Obviously, a grade of Ideal, Excellent, or Very Good would be more that acceptable.... a grade of Good would depend on the diamond and how you feel about it. > Fluorescence- Last, and there is a reason it is last!.... is our little friend, Mr. Fluorescence. I have had some people be so concerned about this one little aspect. I imagine that there most be some "diamond expert" who has put in a book or on their website that diamond fluorescence is some very important characteristic and so it has raised a red flag. Most of the time, diamond fluorescence will not be an important consideration unless it affects how the diamond will look under normal lighting conditions. I've seem diamonds that have fluoresced very strongly under ultraviolet light but looked fine when viewed under fluorescent lighting or outdoors under sunlight. If buying online you might want to draw the line at Medium fluorescence. It is included on diamond grading reports because it is a variable diamond characteristic that could help tie a particular diamond to a particular report. > Plotting Diagram- This is included on diamond grading reports for a few different reasons. First, to link the report to the diamond (like a fingerprint)... if I have 3 different diamonds (with the same weights, clarity, color, and measurements) and 3 different diamond grading reports (different plotting diagrams), I should be able match the diamonds to the reports. This used to happen on a pretty regular basis when I was teaching at GIA.... the students would mix up diamonds by placing a diamond into the wrong parcel paper. A diamond might have a laser inscription of the grading report number on its girdle however laser inscriptions can be polished off. A plot is kind of like a sketch of a person's face. A plotting diagram will also help in supporting the diamond Clarity grade that was assigned to the diamond. The plot below looks pretty busy so it is obvious that it couldn't be a VVS1 diamond. Internal characteristics are plotted in red, and external characteristics are plotted in green. 
- - I went online and looked at some different diamond grading reports, I took a screen shot of one of the reports and then looked up the report detail at the lab's website. Both of these items along with commentary are located here- diamond grading report examples. - - - Important Take Away Points - |
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