What's on an IGI Diamond Certificate (and How to Actually Read One)

If you've bought a diamond at or above 1 carat from us, your piece came with an IGI certificate. Most customers glance at it, notice it looks official, and file it away. Worth doing better than that: this document is a complete technical record of your stone, and reading it properly tells you exactly what you bought and gives you a permanent independent reference for the future. Here's how to actually read one.

What IGI is

The International Gemological Institute (IGI) is one of the major independent gemological laboratories in the world. Founded in Antwerp in 1975, IGI has grading labs in 20+ countries and is, alongside GIA (Gemological Institute of America), one of the two labs most used by the global diamond trade. IGI grades both natural and lab-grown diamonds.

"Independent" is the operative word: the lab does not buy, sell, or have a financial interest in the stones it grades. A customer, jeweler, or supplier sends a stone in, the lab grades it according to a standardized methodology, and a report is issued. The lab's reputation depends on the consistency and accuracy of its grading across millions of stones over decades.

For lab-grown diamonds specifically, IGI was one of the earliest labs to develop a full grading protocol — their reports for lab-grown stones are now an industry standard. For natural diamonds, IGI is well-established alongside GIA, with broadly comparable methodology.

Anatomy of an IGI certificate

Every IGI report contains roughly the same sections, though the exact layout varies slightly between report types (Natural Diamond Report, Laboratory Grown Diamond Report, etc.). Top to bottom, you'll typically see:

1. Report header and number. A unique alphanumeric identifier specific to that stone.
2. Stone identification. Whether the stone is natural or laboratory-grown, the shape and cut (round brilliant, princess, oval, etc.), and growth method for lab-grown stones (HPHT or CVD).
3. Measurements. Length, width, depth in millimeters — the actual physical dimensions.
4. Weight. Carat weight to two decimal places.
5. The 4Cs. Color grade, clarity grade, cut grade.
6. Additional grading details. Polish, symmetry, fluorescence (for natural stones).
7. Proportions diagram. A technical drawing showing the angles, percentages, and proportions of the cut.
8. Clarity plot. A diagram of the stone with inclusions and surface features marked.
9. Comments section. Any additional disclosures (treatments, laser inscriptions, special features).
10. Verification details. Date issued, IGI seal, and how to verify the report online.

The 4Cs as they appear on the report

The 4Cs are the four core grading characteristics, presented on every diamond report.

Carat (weight)

Expressed as a decimal: 1.01ct, 1.50ct, 2.07ct. Carat is a unit of weight, not size. A well-cut 1ct stone can look larger or smaller than a poorly-cut 1ct stone depending on its proportions. Carat is also rounded — a stone graded 0.99ct cannot be sold as "1ct," which is why you'll occasionally see prices jump dramatically at the 1.00 and 2.00 carat thresholds.

Color

For white diamonds, color is graded on the D–Z scale:

• D–F: Colorless. The highest grades. D is rarer (and more expensive) than E or F, but the difference is invisible to almost everyone without lab equipment.
• G–J: Near-colorless. The category where most engagement-ring diamonds fall. G and H look colorless face-up in most settings; I and J may show very faint warmth.
• K–M: Faint yellow. Noticeable in white gold or platinum settings; less noticeable in yellow gold.
• N–Z: Very light to light yellow.

For fancy-color diamonds (including the cognac and champagne stones in our Brownstone Collection), the D–Z scale doesn't apply. They're graded separately on hue, tone, and saturation, with terms like Fancy Light Brown, Fancy Brown, etc.

Clarity

Graded based on the presence and visibility of internal inclusions and surface blemishes under 10x magnification:

• FL / IF: Flawless / Internally Flawless. Extremely rare, top of the scale.
• VVS1 / VVS2: Very Very Slightly Included. Inclusions hard to see even under 10x magnification.
• VS1 / VS2: Very Slightly Included. Inclusions visible under 10x but not to the unaided eye.
• SI1 / SI2: Slightly Included. Inclusions visible under 10x; may be visible to the unaided eye in some stones.
• I1 / I2 / I3: Included. Inclusions clearly visible to the unaided eye.

For most engagement-ring and fine-jewelry purposes, VS1–VS2 represents the practical sweet spot: stones look clean to the naked eye, cost dramatically less than VVS or IF, and have inclusions only a gemologist would notice.

Cut

Cut grade applies primarily to round brilliant diamonds, where there's a clearly defined mathematical ideal. Other shapes (oval, princess, emerald, marquise) are graded on polish and symmetry but don't get a single overall "cut grade" the way rounds do.

• Excellent / Ideal: The stone's proportions, symmetry, and polish maximize light return.
• Very Good: Very close to ideal; small deviations that don't materially affect appearance.
• Good: Acceptable cut, may show some light leakage.
• Fair / Poor: Significant proportion problems. We don't carry stones in these grades.

Cut grade is the most underrated of the 4Cs. A stone with average color and clarity but excellent cut will outperform a stone with better color and clarity but worse cut. Pay attention to cut.

Measurements and proportions

Beyond the headline 4Cs, the report includes physical measurements and a proportions diagram. For a round brilliant, you'll see:

• Measurements: Diameter min — Diameter max — Depth, in millimeters. Example: 6.42 — 6.46 × 3.98 mm.
• Table %: The size of the flat top facet as a percentage of total diameter. Typical excellent range: 54–60%.
• Depth %: The stone's depth as a percentage of its average diameter. Typical excellent range: 60–62.5% for round brilliant.
• Crown angle, pavilion angle, girdle thickness: Geometric specifications of the cut.
• Culet: The small facet (or point) at the bottom of the stone. Modern stones usually have "None" or "Very Small."

These numbers matter for verifying the stone is the one described on the report. If you ever want to confirm that a stone hasn't been swapped (extremely rare with reputable retailers but worth knowing how), measuring the stone and matching dimensions to the certificate is the standard verification.

The clarity plot

The clarity plot is the diagram of the stone with marks showing where inclusions are located. Red marks typically indicate internal inclusions; green marks indicate surface blemishes. The clarity plot is essentially your stone's fingerprint — the specific pattern of inclusions is unique and can be used to identify your stone for life, even decades from now.

If your stone is graded VS1 or higher, the clarity plot may be very sparse — only one or two small marks. SI grades typically have more marks. The plot doesn't indicate quality directly; it indicates location, and how the gemologist evaluated the stone's clarity grade.

Additional comments and notes

The Comments section is small but important. Things that can appear here:

• Laser inscription: Many lab-grown diamonds (and some natural diamonds) have a microscopic inscription on the girdle with the report number. If your stone is inscribed, the report will note it.
• Treatments: If a stone has been treated in any way (HPHT post-growth treatment for some lab-grown, fracture filling, laser drilling for some natural), it will be disclosed here.
• Color origin notes: For fancy-color diamonds, any relevant notes about the color's source.
• Special features: Anything else the gemologist felt should be on record.

For our customers: untreated stones with no special comments — which is the standard case — will have a blank or minimal comments section. That's a good sign, not a problem.

IGI vs GIA — the honest comparison

This is the question we get most often after "what does the report mean."

GIA (Gemological Institute of America) is the older and historically more prestigious of the two labs, particularly for natural diamonds. It's the original developer of the 4Cs grading system. GIA reports tend to command slightly higher resale prices in the natural diamond market and are sometimes preferred by very high-end buyers.

IGI is the global leader in lab-grown diamond grading and has comparable methodology to GIA for both stone types. Their reports are accepted throughout the global diamond trade. IGI grades the majority of lab-grown diamonds sold in retail jewelry today.

Factor	IGI	GIA
Founded	1975 (Antwerp)	1931 (Los Angeles)
Lab-grown grading	Industry standard	Strong, more recent entry
Natural diamond grading	Well-established	Historically the benchmark
Cost per stone graded	Generally lower	Generally higher
Color grading strictness	Slightly more lenient (~half a grade)	Slightly stricter
What we use	Our standard for 1ct+	Available on request

For the customers we serve, IGI is the right choice. It's the dominant lab for lab-grown stones (which is most of what we sell), the cost is sensible, and the grading is accepted across the industry. If you specifically want a GIA report — typically for very high-value natural diamonds where the resale premium matters — we can source GIA-graded stones, but it'll add to the lead time and cost.

Why we certify at 1ct and not below

Our standing policy is that every diamond at or above 1.00 carat in our work comes with an IGI grading certificate. Stones below 1ct do not get individual certificates. A few reasons:

• Cost to certify a 0.20ct stone often exceeds the wholesale stone cost itself. Adding a $50–$100 grading fee to a small accent stone pushes the price of finished pieces up without giving the customer meaningful additional confidence.
• Smaller stones are typically sourced in melee parcels of consistent grade. The supplier provides quality assurance at the parcel level, which is the trade standard for stones under 1ct.
• The 1ct threshold is where individual certificates become genuinely useful — for resale documentation, for insurance, for identifying the specific stone if it's ever lost.

We're reviewing this policy regularly. As lab-grown supply continues to scale and certification costs drop, the threshold may come down. If it changes, customers will know.

How to verify your certificate is real

Every IGI report has a unique number printed on it. To verify the report is legitimate:

1. Go to igi.org.
2. Use the Report Check feature.
3. Enter the report number from your physical certificate.
4. The site will display the original report data — if it matches what's on your paper certificate, the certificate is genuine.

This takes 30 seconds and is worth doing once for any major purchase, even from a reputable retailer. Counterfeit certificates are rare in mainstream retail but do exist in the secondary market and at the edges of the industry.

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Diamond disclosure: Unless otherwise noted, diamonds featured at Black Pearl of Queens are laboratory-grown. Brownstone Collection pieces feature natural cognac and champagne diamonds, sourced primarily from Canada, South Africa, Botswana, and Namibia, and accompanied by IGI grading for stones 1ct and above. Learn more about our diamond sourcing.