Reading a diamond certificate (Diamond Grading report)

First a quick note. GIA has contacted us requesting that we use the term Diamond Grading Report rather than Certificate. Their concern seems to be that a Certificate might imply that the lab is certifying the diamond, which some may view as an endorsement of the item rather than a description. That is an important distinction, one that probably came years after GIA's lab started offering reports. However people in the trade still use the term certificate or cert for short. So we will respect GIA's wishes, but want you to be aware of the issue.


Before we dive into the anatomy of an actual Diamond Grading Report, it is important to understand the purpose of the Report. A Diamond Grading Report is a statement, issued by an independent Gemological Laboratory, that at the time of evaluation, the Diamond in question has been examined by experienced Diamond Graders, using various gemological instruments, and determined to contain the characteristics as stated in the Report. As we discuss the various elements contained in the report, we will describe which gemological instruments were used to evaluate the specific property under discussion.

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 mistakenly purchase a Diamond of lower value, believing it to be of higher value.

Note that since this article was first written, different versions of diamond grading reports have come out. We do revisit this page from time to time to make sure new elements are incorporated into the article. But if the report you have does not look exactly the same as these pictures, do not worry.


We recommend strongly that you do not buy any diamond without a Grading Report. GIA is the foremost Laboratory in the world, though there are other reputable labs out there. However, not all labs are made alike. GIA created the standards and all respectable labs follow them. They have the best instruments and the most advanced gem lab in the world. That's why all the most important diamonds in the world carry GIA reports. From the Hope Diamond to the Heart of Eternity, the Millennium Star, the Tiffany, the Premier Rose and The Incomparable.

If you found a Diamond you like, and it is not certified (i.e. does not carry a grading report) there is nothing wrong with asking your Jeweler to send it to GIA. If your Jeweler has a problem with that, then you should start asking your jeweler and yourself more questions! This request is a standard practice in the Diamond Industry.

What's in a name?

The number one most important item to look for on a Diamond Grading Report is the name of the laboratory! If you never heard of the Laboratory, do some research on them. Post a note in our forum asking about them.

Search for the word "Lab" in our Forum.

Certificate (Grading Report) Number

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 cert number, they can even reissue a certificate (report) if you lose it.

Search for the word "Certificate" in our Bulletin Board.

Laser Inscription Registry

The laser inscription registry refers to the fact that all diamonds receiving a GIA Diamond Dossier® is micro-laser inscribed with its unique GIA Report number.

Shape and Cutting Style

Shape refers to the outline of the diamond. Examples include:
Round, Pear, Heart and Oval.
Cutting Style refers to the facet arrangement. Examples include:
Brilliant, Marquise, Emerald, Princess, Step and Mixed.

Search for the word "Cut" in our Forum.

Measurements

Measurements of the Diamond's diameter:
For round diamonds these would be "minimum diameter - maximum diameter x depth" whereas for fancy shape diamonds it would be "length x width x depth". These measurements are calculated to the hundredth of a millimeter by a non-contact measuring device or a micrometer.

Search for the word "Measurement" in our Bulletin Board.

Size Matters

Diamonds are weighed to the thousandth of a carat with a digital measuring device. On the grading report, weight is rounded to the hundredth of a carat.

Add Color to your Day

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.

Search for the word "Color" in our Bulletin Board.

On a Clear Day you can see Diamonds Are Forever

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.

Search for the word "Clarity" in our Bulletin Board.

Cut Grade

The Cut Grade is a new feature of the GIA report.

Finish, Polish & 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 aligned to each other. It is easy to detect this property with a loupe. Look at the table of your Diamond. Does the right side look like a mirror of the left? Do all the facets have more or less the same shape, or do they vary greatly?

Polish Excellent Very Good Good Fair Poor and Symmetry Excellent Very Good Good Fair Poor

Search for the word "Symmetry"  in our Bulletin Board.

Fluorescence

Fluorescence refers to a Diamond's reaction to long wave ultraviolet radiation. If a Diamond has too much fluorescence, some feel strong fluorescence can make a Diamond less desirable. Below are example values for Fluorescence.

Fluorescence None VeryFaint Faint FaintBlue MediumBlue StrongBlue VeryStrongBlue FaintYellow MediumYellow StrongYellow VeryStrongYellow

Search for the word "Fluorescence" in our Bulletin Board.

Comments, Comments, 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.

The Plot Thickens!

A 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.

Key to symbols

The key to symbols helps you identify characteristics marked in the plot.

Security Features

There are several security features in place to make it hard to forge a grading report, including upc codes and a hologram. If you want to make sure that a diamond matches the grading report, have an independent appraiser, one who does not sell diamonds, verify the report for you. The reason the appraiser needs to be independent is so that there is no conflict of interest. An appraiser who would love to sell you a diamond is less likely to be fair to a diamond you bring in than someone who doesn't sell or get a commission for a diamond sale.

A picture speaks a thousand words

Gia has modified their report to include proportion information in graphical format. The following sections will only appear in older reports.

It's all Proportional

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 help determine how "well" the Diamond has been cut.

Search for the word "Proportion" or "Depth" or "Table" in our Bulletin Board.

Girdles

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. You may also see some diamonds with a laser inscription right on the girdle. It is relatively inexpensive to have a custom message inscribed and it doesn't affect carat weight. Below are example Girdle Thicknesses.

GirdleThickness ExtremelyThin VeryThin Thin Medium SlightlyThick Thick VeryThick ExtremelyThick to GirdleThickness VeryThin Thin Medium SlightlyThick Thick VeryThick ExtremelyThick , Not Faceted Faceted PartiallyFaceted

Search for the word "Girdle" in our Bulletin Board.

Culet

The Culet of a Diamond, if there is one, is the facet on the pointy bottom part of the Diamond. Its existence helps prevent chipping. Below are possible culet sizes.

Culet None Very Small Small Medium SlightlyLarge Large VeryLarge ExtremelyLarge

Where's the value?

Value or price is not included in a Diamond Grading Report. The grading report reflects quality only, not pricing. The report is meant to be valid long after market prices have changed. If you want a paper to certify value at time of purchase for insurance purposes, get an appraisal. It might be a good idea to contact your insurance broker to find out what type of appraisals they accept and what the replacement value will be based on.

SI3

If you have a certificate with an SI3 grade, you might like to know what it means. There has been talk for years about introducing an SI3 grade to further subdivide the range between SI2 and I1 stones. EGL - Los Angeles, (European Gemological Laboratory) started to give out SI3 grades, followed by the "Rap Sheet" (a trade-publication of Diamond prices), incorporating SI3 into their price list as well. Therefore, many feel the SI3 grade has "made it". While we do believe that there is nothing wrong with the concept of the SI3, the fact that GIA does not recognize it makes the SI3 grade less valuable.