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Diamond Grading Report: Why you need it and what it is telling you.
A Diamond Grading Report issued by an Independent Gemological Laboratory, tells you that the Diamond has been examined by experienced Diamond Graders, using various gemological instruments, and contains the characteristics as stated in the Certificate.
The reason it is important to have a Diamond evaluated by an independent Laboratory is that minute, invisible to the naked-eye, characteristics of a Diamond can have a major influence on the price. Therefore, if not for a great deal of scrutiny on the part of the buyer, it is easy to mistake and purchase a Diamond of lower value, believing it to be of higher value.
I strongly recommend that you do not buy any diamond without a Diamond Certificate. GIA is the foremost Laboratory in the world, though there are other reputable labs out there. However, not all labs are equal in their grading stringency, accuracy, and consistency.
If you found a Diamond you like, and it is not certified there is nothing wrong with asking your Jeweler to send it to a reputable independent Gemological Laboratory for certification. If your Jeweler has a problem with that, take a few steps back and ask yourself many more questions! This request is a standard practice in the Diamond Industry.
What's in a Diamond Lab name?
The number one most important item to look for on a Diamond Certificate is the name of the laboratory! If you never heard of the Laboratory, don't feel shy about giving them a call to check them out. Also, if the laboratory is an independently owned franchise and the certificate you were given is not local, you may want to call up the lab, either the local one or the one that issued the certificate, and ask them by which standards they grade their Diamonds. Find out if they honour the grades given out by other branches.
GIA is the foremost grading laboratory in the world both for their excellence in diamond and gemstone grading as well as for their comprehensive research and educational programs to both the trade and consumers.
Actual GIA Grading Report:
Basic Parts of a Round Brilliant Diamond.
Let's go over this report and examine the information it gives you:
Every lab has a certificate (or " report") number, which uniquely identifies a Diamond. The Lab keeps an internal copy of everything which you see on the certificate, plus some additional information for their files. If you call up the Lab and give them the certificate number, they can even reissue a certificate if you lost it. This report number is found in the upper left-hand margin and appears vertically. The Cert number for the GIA report shown here is: 11510402.
Diamond Shape: Self explanatory.
Measurements: Measurements of the Diamond's diameter:
"minimum - maximum x depth" are calculated to the hundredth of a millimeter by a Leveridge Guage or a micrometer.
Weight: Diamonds are weighed to the thousandth of a carat with a digital measuring device. On the certificate, weight is rounded to the hundredth of a carat. Diamonds are always measured in carat weight. One carat is the equivalent of 1/5 of a gram. Additionally, there are "100" points in a carat, so that a .50 "point" diamond would be described as a half-carat.
In general, the pricing structure for polished diamonds is directly related to the pricing structure for the diamonds in their rough state. Because there is a scarcity of large diamond rough, the price for these diamonds after polishing will be higher per carat. As you get larger in carat weight there will be an incremental jump in price even between two diamonds of same color and clarity. These plateaus are found approximately every .10-.15 points. Category examples are: .50-.59, .60-.69, .80-.89, .90-.99 carat, etc.
Proportions: Depth Percentage and Table Percentage are measured.
Depth percent refers to the percent of the depth of the Diamond, table to culet, relative to the width of the stone.
The Table of a Diamond refers to its largest facet, the main part of the Diamond you look at when the stone is face-up.
Table percent refers to the table size as a percentage of the Diamond's average width.
These ratios in conjunction with the Millimeter measurements indicate how "well" the Diamond has been cut.
Girdle: The Girdle of a Diamond is the dividing line between the crown, or top part of the stone and the pavillion, or bottom part of the stone. Girdle thickness can be very thin in part of a stone and very thick in another part. That is why it is expressed as a range. The girdle can also be faceted, or not. A faceted girdle usually improves the look of the stone, and involves having the cutter polish facets into the girdle.
Culet: If there is one, is the facet on the pointy bottom part of the Diamond. Its existence helps prevent chipping.
Finish of the Diamond, referred to as Polish and Symmetry:
Finish describes the polish of a Diamond and how symmetrical, or how evenly, the facets have been placed.
Polish refers to the quality of the polish on the facets. An excellent polish reflects the care taken by the Diamond cutter.
Symmetry refers to how precisely the facets are externally aligned to each other. All the facets should have more or less the same shape and size.
Clarity Grade:
Clarity ranges from the best grade of IF, down through VVS1, VVS2, VS1, VS2, SI1, SI2, I1, I2 until I3. Clarity is a reflection of the number, size, placement and nature of inclusions and/or surface irregularities on the Diamond. The experienced Diamond Grader examines the Diamond with the aid of a Stereo Microscope, which aids in identifying the nature of an inclusion, or finding pinpoints (very, very tiny crystals inside the Diamond). However, the actual grade is based only on what is visible under a 10X Loupe.
Color:
Color ranges from the best grade of D, down to Z. After Z are Fancy Colors. Color grade is determined by examining the Diamond next to a master set of color comparison stones, under special lighting.
Fluorescence:
Fluorescence refers to a Diamond's reaction to long wave ultraviolet radiation. Fluorescence or blue diamonds is a hotly debated topic with much erroneous information being disseminated to consumers.
Read this link on our Blog for more detailed and accurate information on blue diamonds. Blue Diamonds
The Diamond Plot:
The Diamond Plot is a graphical representation of the imperfections of the Diamond. Each Diamond is as unique as a fingerprint. By plotting its characteristics, and combining this with the physical measurements of a Diamond, a Lab can uniquely identify each stone. This plot helps the Grader in the even that a customer returns to the Lab and requests a verification that the Diamond presented with a certificate refers to the same Diamond described in the Certificate.
Internal characteristics are plotted in red, and external characteristics are plotted in green.
Comments:
Comments are used to describe characteristics not discussed elsewhere on the certificate, or to mention items not plotted. For example, "minor details of polish are not shown" is a common comment. "Crown angles over 35 degrees", or Crown angles under 30 degrees" are other comments pertaining to Cut that may also appear.
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Comments
I'm wondering if your acquainted with our eCS system of Cut Grading. We have checked it statistically and mathematically to determine it's accuracy. It has no tolerance from IDEAL to a cut less than to include it in the EXCELLENT OR "O" category. When the eCS is equal to 1.000 then the cut is IDEAL; anything less is just that .999 or less. And we give the calculation away for FREE at our web site at www.e-praise.com click on the leveridge gauge on the bottom left of the front page. It, by the way calculates the eCS for any shape diamond
Posted by: Merv Cohn on August 16, 2006 4:33 PM
Merv,
I am not familiar with it, my Dad (Barry) might be though.
Hopefully, he chimes in here.
May I ask you for some information on how exactly you derive your calculations for something (optical beauty) that by definition is often completely subjective and personal?
Any insight would be appreciated.
Best of luck to you!
Judah
Posted by: Judah on August 16, 2006 4:50 PM
Is it typical to get a grading report on diamonds if they are channel set within a band and are less than 1/2 a carat total weight?
Thanks!
Posted by: alissa on June 30, 2007 10:45 AM