The Document That Tells the Truth

A diamond certificate (also called a grading report) is the only objective evidence of a diamond is quality. Without one, you have only the seller is word. With one from a reputable laboratory, you have proof. This guide walks you through a GIA or IGI certificate section by section so you know exactly what you are looking at when you read one.

Laboratory Identification

The first thing to check on any certificate is which laboratory issued it. GIA (Gemological Institute of America) and IGI (International Gemological Institute) are the two most widely accepted gemological laboratories. A certificate from any other laboratory should be treated with more caution—some labs have lower standards and may grade more generously (which benefits sellers, not buyers).

The certificate number is unique to your diamond and is usually inscribed on the diamond is girdle (the outer edge). This allows the physical diamond to be linked to its certificate.

Shape and Cutting Style

Near the top of the certificate, you will find the shape (round, oval, emerald, etc.) and cutting style (brilliant, step, mixed). This confirms the diamond is what the seller says it is. If the certificate says oval but the seller described a round, there is a problem.

Measurements

The measurements section gives the diamond is dimensions in millimeters, typically shown as length x width x height. These numbers tell you the physical size of the diamond and can be used to calculate the diameter of round diamonds or the length-to-width ratio for fancy shapes.

For round brilliants, the diameter is usually given as a range (e.g., 6.35-6.40mm) because most are not perfectly round. A diameter of 6.50mm at its widest point and 6.45mm at its narrowest is normal.

The 4 Cs

Carat Weight

Carat is the weight of the diamond, measured in metric carats (1 carat = 0.2 grams). The carat weight is listed to the nearest hundredth of a carat (e.g., 1.03 carats). Two diamonds of the same carat weight can look very different in size if their cuts differ, so never judge size by carat weight alone.

Color Grade

Color is graded on a scale from D (completely colorless) to Z (noticeable brown or yellow). The differences between adjacent grades are subtle and usually invisible to the untrained eye.

• D, E, F: Colorless. The highest grades. Expensive.
• G, H: Near-colorless. Excellent value—appears colorless in most settings.
• I, J: Near-colorless. May show slight warmth in white metal settings. Good value.
• K and below: Increasing visible warmth. Less expensive.

Clarity Grade

Clarity measures inclusions (internal flaws) and blemishes (external flaws). The scale runs from FL (Flawless) to I3 (Included). Most diamonds fall in the VS (Very Slightly Included) or SI (Slightly Included) range.

• FL, IF: No inclusions or blemishes visible under 10x magnification. Rare and expensive.
• VVS1, VVS2: Inclusions extremely difficult to see under 10x. Expensive.
• VS1, VS2: Minor inclusions. Good practical choice—usually eye-clean and less expensive than VVS.
• SI1, SI2: Noticeable inclusions under 10x. SI1 diamonds often appear eye-clean. Good value.
• I1, I2, I3: Inclusions visible to the naked eye. Generally not recommended for engagement rings.

Cut Grade (Round Brilliant Only)

GIA grades cut only for round brilliant diamonds. The cut grade evaluates brightness, fire, and scintillation, and ranges from Excellent to Poor. An Excellent cut diamond returns maximum light and sparkles beautifully. A Poor cut diamond appears dull or dark.

For fancy shapes (oval, pear, emerald, etc.), cut is not graded by GIA. This does not mean cut does not matter—it does—but there is no standardized cut grade for fancy shapes.

Proportions

The proportions section contains specific measurements of the diamond is cut:

• Table %: The width of the flat top facet relative to the total width of the diamond. Affects brilliance.
• Depth %: The total depth relative to width. Affects light return.
• Crown angle: The angle of the crown facets. Affects fire and brilliance balance.
• Pavilion depth: The depth of the pavilion relative to width.

These numbers matter more for round brilliants than for fancy shapes. For round brilliants, look for proportions within the ideal range: table 53-58%, total depth 59-62.5%, crown angle 33-35 degrees.

The Diagram (Clarity Plot)

The clarity plot is a map of the diamond showing the location, type, and relative size of inclusions. This is one of the most useful parts of the certificate because it shows you exactly what is inside the diamond, not just a clarity grade.

Common inclusion symbols:

• Feather: A small fracture in the diamond. Generally not a durability concern unless it reaches the surface.
• Cloud: A cluster of tiny inclusions too small to see individually. Can affect transparency if dense.
• Crystal: A mineral inclusion trapped inside the diamond. Can be white (diamond crystal) or colored.
• Needle: A long, thin inclusion.
• Pinpoint: A single tiny inclusion.

Finish Grades

Finish grades evaluate the quality of the diamond is polish (the smoothness of the surface) and symmetry (how precisely the facets are aligned). Grades range from Excellent to Poor. Both are usually graded on the same scale. Excellent polish and symmetry are important for maximum light return, but minor deviations are usually invisible to the naked eye.

Comments

The comments section discloses any additional information that does not fit the standard grading categories. Common comments include:

• Inscription: Notes that the diamond girdle is inscribed with the certificate number.
• Treatment disclosure: Notes that the diamond has been treated (e.g., HPHT processed to improve color).
• Key of symbols: References the symbols used in the clarity plot.

How to Verify a Certificate

Before purchasing, always verify the certificate by entering its number on the issuing laboratory is website. GIA certificates can be verified at reportcheck.gia.edu. IGI certificates can be verified at igi.org. This confirms the certificate is genuine and the diamond matches the report.

At Aranc

We provide certificates with every diamond and encourage all buyers to verify their certificate before purchase. If you have questions about a specific certificate, our team is happy to walk you through it.