How to Read an IGI Certificate: The Details Everyone Misses

You receive a PDF. It says: 1.00ct, D, VVS1, Excellent Cut.

Perfect, right? You wire the money.

Then the stone arrives, and something feels... off. The brilliance isn't what you expected. Under certain lights, it looks slightly gray.

What went wrong?

The Problem: Most Buyers Only Read the Top Half

The 4Cs (Carat, Color, Clarity, Cut) are prominently displayed at the top of every IGI certificate. But the real information is buried in the fine print.

Section 1: The Comments Section (Most Important!)

At the bottom of every IGI report, there's a "Comments" section. This is where IGI discloses issues that don't fit into the standard grading categories.

Red Flag Comments to Avoid:

• "Blue Nuance" — The stone has a blue tint caused by boron. Common in HPHT. Kills value.
• "Brown Nuance" — Brownish tint. More common in CVD. Also kills value.
• "Clarity Grade Based on Clouds Not Shown" — The stone has internal cloudiness that doesn't show up in the plot. This means it will look hazy in person.
• "Surface Graining" — Visible lines on the surface. Affects brilliance.

If you see ANY of these comments, demand a discount or walk away.

Section 2: Fluorescence

Fluorescence is how a diamond reacts under UV light. For natural diamonds, strong fluorescence can be a negative. For lab-grown diamonds, it's more nuanced.

HPHT Diamonds: Often have "None" or "Faint" fluorescence. This is normal and desirable.

CVD Diamonds: Can have "Medium" to "Strong" fluorescence, especially if they've been post-growth treated to improve color.

Rule of Thumb: For D-E-F color stones, prefer "None" or "Faint" fluorescence. For G-H-I, it doesn't matter as much.

Section 3: The Clarity Plot

The clarity plot shows the location and type of inclusions. Here's what to look for:

• Inclusions Under the Table: Bad. These are visible face-up and affect brilliance.
• Inclusions Near the Girdle: Better. Less visible, can often be hidden by prongs.
• Black Inclusions: Worse than white inclusions. Black spots (carbon or metal) are more noticeable.

Pro Tip: A VVS2 with inclusions near the edge is often more "eye-clean" than a VVS1 with a centered inclusion.

Section 4: Cut Grade Breakdown

IGI provides an overall cut grade (Excellent, Very Good, etc.), but they also break it down into components:

• Polish: Surface finish quality
• Symmetry: How precisely the facets are aligned
• Proportions: Table %, depth %, crown angle, pavilion angle

Ideal Proportions for Round Brilliants:

• Table: 54-58%
• Depth: 59-62.5%
• Crown Angle: 34-35°
• Pavilion Angle: 40.6-41°

If the proportions are outside these ranges, the stone may have light leakage (looks dull) or a "fisheye" effect (dark center).

Section 5: Growth Method

IGI clearly states whether a stone is HPHT or CVD. But here's what they DON'T tell you:

• HPHT stones can still be post-growth treated (annealed) to improve color. This is not disclosed.
• CVD stones are almost always post-growth treated (HPHT annealing) to remove brown tint. This is also not disclosed.

How to Tell: If a CVD stone is graded D-E-F with no "Brown Nuance" comment, it's been treated. This is standard practice and not a problem—just be aware.

The One-Minute Certificate Review Checklist

Before you buy, check these 5 things:

1. Comments section — Any red flags?
2. Fluorescence — Appropriate for the color grade?
3. Clarity plot — Inclusions under the table?
4. Proportions — Within ideal ranges?
5. Report number — Verified on IGI.org?

If all 5 check out, you're good to proceed.