How Do I Read a Diamond Certificate?
A diamond grading report — often called a "certificate," though "report" is the correct industry term — is organised into clearly defined sections. Reading it top to bottom takes you from the diamond's identity to its grades to its visual detail. Once you understand the layout, any report from GIA, HRD, or IGI becomes straightforward to interpret.
The Header: Identity and Report Details
The top of the report identifies the document itself: the laboratory name, report number, date of issue, and the type of report (for example, GIA Diamond Grading Report or GIA Diamond Dossier). The report number is your key reference — it links to the laboratory's online verification database and, in many cases, to a laser inscription on the diamond's girdle.
Shape and Cutting Style
This section tells you what kind of diamond was examined: round brilliant, oval modified brilliant, emerald cut (step cut), and so on. It confirms the shape you expect and clarifies the cutting style, which affects how light interacts with the stone.
Measurements
Three numbers appear here — for a round diamond, minimum diameter, maximum diameter, and total depth in millimetres (e.g., 6.41–6.44 × 3.98 mm). For fancy shapes, these become length, width, and depth. These measurements determine the diamond's face-up size and are essential for setting compatibility.
The 4Cs Panel
This is the core of the report:
- Carat Weight — recorded to the hundredth of a carat (e.g., 1.01 ct)
- Colour Grade — on the D-to-Z scale for colourless-to-light diamonds, or a descriptive grade for fancy colours
- Clarity Grade — from Flawless (FL) to Included (I3), based on the visibility of inclusions and blemishes under 10x magnification
- Cut Grade — for round brilliants on GIA reports, graded Excellent to Poor. Fancy shapes do not receive a GIA cut grade
Each grade results from standardised assessment procedures. They are the common language the market uses to compare and price diamonds.
Finish: Polish and Symmetry
Below or alongside the 4Cs, you will find polish and symmetry grades (Excellent to Poor). Polish refers to the smoothness of the facet surfaces. Symmetry refers to the alignment and consistency of the facet arrangement. Both contribute to light performance but are rarely the deciding factor unless they fall below Very Good.
Fluorescence
This section records whether the diamond emits visible light under long-wave ultraviolet radiation, and if so, how strongly (None, Faint, Medium, Strong, Very Strong) and in what colour (typically blue). Fluorescence can affect appearance — sometimes positively, sometimes negatively — depending on the diamond's colour grade and the fluorescence intensity.
Clarity Plot
The clarity plot is a diagram of the diamond showing the approximate location, type, and relative size of notable inclusions and blemishes. Common symbols represent crystals, feathers, clouds, needles, and other characteristics. This is one of the most informative sections of the report — it tells you not just the grade, but where the inclusions sit and what type they are. An inclusion near the edge of the diamond has a very different visual impact than one beneath the table.
Proportions Diagram
A cross-section diagram showing key angles and percentages: table percentage, total depth percentage, crown angle, pavilion angle, girdle thickness range, culet size, and star and lower-half facet lengths. These proportions determine how the diamond handles light. For round brilliants, GIA's cut grade synthesises this data, but the individual measurements let you evaluate the stone at a more granular level.
Comments
The comments section records additional observations: whether the diamond has been laser-inscribed, whether specific clarity characteristics are not shown on the plot, whether the stone has undergone any treatments, and other notes the grading team considered relevant.
How to Use the Report
Read the 4Cs first for the broad picture, then study the clarity plot and proportions diagram for the detail. The grades tell you the category; the plot and diagram tell you the character. Two diamonds with identical grades but different clarity plots and proportion sets can look and perform quite differently.
At Arete Diamond, every stone comes with the full grading report alongside HD video and detailed data, so you can see how the grades translate into actual appearance.
Learn More
- How to Read a Report — our comprehensive section-by-section guide
- The 4Cs Panel on a Report — what each grade line means
- The Clarity Plot — how to interpret inclusion symbols and positions
- The Proportions Diagram — reading angles, percentages, and what they control