📜 How to Read a Diamond Certificate: IGI, and What Those Letters Actually Mean

A lot of people think lab-grown diamonds don’t come with certificates. That’s not true.

A certified lab-grown diamond carries a grading report just as detailed as any mined stone. 

IGI (International Gemological Institute) is the global authority in lab-grown diamond grading. Out of every 10 lab-grown diamonds on the market, 6 to 7 are certified by IGI. Today, we’ll walk you through an IGI certificate step by step—so you’ll never feel lost in professional term again.

1.What Does an IGI Certificate Look Like?

When you open an IGI lab-grown diamond report, you’ll find these core sections:Diamond Identification:

• Certificate number, date, laser inscription (if applicable)
• 4C Grading Results: Carat, color, clarity, cut
• Proportions Diagram: Shows the actual cutting proportions of the diamond
• Clarity Plot: Marks the location and type of inclusions
• Comments Section: Additional notes, such as whether post-growth treatment has been applied

2.What Should You Look at First?
🔍 Check the Title: Confirm It’s a Lab-Grown Diamond
At the top of the certificate, it clearly states:

"LABORATORY GROWN DIAMOND REPORT"

This is a statement of identity. IGI uses the exact same grading standards for lab-grown and natural diamonds, but clearly distinguishes them in the title—this is the industry standard for transparency.

🔢 Check the Certificate Number
Every IGI-graded diamond has a unique certificate number. If your diamond has been laser inscribed, this number is micro-engraved onto the girdle and can be seen under 10x magnification.

3. How to Read the 4C
💎 Carat Weight
The most straightforward number. 1 carat = 0.2 grams. But remember: carat is weight, not size. A well-cut diamond can appear larger than its carat weight suggests.

🎨 Color Grade
IGI uses the D-to-Z color scale:

• D–E–F: Colorless (rarest, highest price)
• G–H–I–J: Near colorless (best value; yellow tint nearly invisible to the naked eye)
• K and below: Faint yellow to light yellow (not recommended for everyday wear unless part of a specific design)

Pro tip: For mounted rings, H-color and above appear colorless to most people. Put your budget toward a larger carat or better cut instead.

🔬 Clarity Grade
IGI clarity grades from highest to lowest:

• IF: Internally Flawless (extremely rare)
• VVS1–VVS2: Very Very Slightly Included (hard to see under magnification)
• VS1–VS2: Very Slightly Included (visible under magnification)
• SI1–SI2: Slightly Included (clearly visible under magnification, some visible to the naked eye)
• I1–I2–I3: Included (visible to the naked eye—not recommended)

Key point: Lab-grown diamonds can have inclusions too! CVD diamonds may contain dark carbon spots; HPHT diamonds may have traces of metal flux. The certificate is honest about them. We recommend VS2 or higher for guaranteed eye-cleanliness.

✂️ Cut Grade
This is the only grade determined by human craftsmanship—and it directly affect a diamond's brilliance and fire:

• Excellent: Reflects nearly all light; the most brilliant
• Very Good: Reflects most light; great value
• Good: Reflects most light but slightly less brilliance
• Fair / Poor: Not recommended

Rule of thumb: For round diamonds, only choose Excellent or Very Good cut. Fancy shapes (like oval or pear) don't receive a cut grade, but you'll see "Symmetry" and "Polish" grades instead.

4. Don't Miss These Details
📐 Proportions Diagram
The diamond outline in the middle of the certificate shows:

• Table percentage
• Crown angle
• Pavilion depth

Don't worry if these numbers mean nothing to you. If the cut grade is Excellent or Very Good, the proportions are within ideal ranges.

🔍 Clarity Plot
Symbols mark the position of inclusions:

• Red dots/circles: Inclusion locations
• Green: Markers with no clarity impact

If you're a perfectionist, check whether inclusions are under the table (visible from the top) or near the edge (may be obscured after being embedded).

📝 Comments Section
This is the most important section! It will note:

• Whether post-growth treatment has been applied (e.g., HPHT annealing for color enhancement)
• Whether laser inscription is present
• Other special notes

For untreated diamonds, the certificate will clearly state: "No indications of post-growth treatment" This means the diamond grew naturally in the lab without any artificial color or clarity enhancement after growth.

5. Three-Step Reading Guide

6. Sample IGI Certificate Interpretation (Example)
Imagine the certificate reads:

Carat Weight: 1.50 ct
Color Grade: F
Clarity Grade: VS1
Cut Grade: Excellent
Comments: No indications of post-growth treatment

What does this mean?

• 1.50 carat, F color, VS1 clarity, Excellent cut—a high-quality lab-grown diamond
• No post-growth treatment—grown naturally in the lab, pure and untreated

7. Frequently Asked Questions
Q: Which is more authoritative, IGI or GIA?
Both are internationally authoritative. IGI has deeper experience in lab-grown diamonds, holding about 65% of the market. GIA recently simplified its lab-grown diamond grading. For consumers, both are trustworthy.

Q: Does the certificate date matter?
The date shows when the diamond was graded—it doesn't affect quality. But if the certificate is several years old, confirm whether the diamond is still available and priced fairly.

Q: Do lab-grown diamond certificates say "synthetic"?
No. IGI uses "Laboratory Grown"—the international standard term. It's more accurate and respectful than "synthetic."

8. Summary
By learning to read an IGI certificate, you can:

• Confirm you're buying a real lab-grown diamond
• Judge whether the quality matches the price
• Avoid purchasing post-treated stones
• Choose the one that truly deserves your investment

A certificate isn't just a piece of paper. It's your diamond's complete biography—honestly telling you where it came from, how it grew, and whether it's been touched up.

Next time you hold an IGI certificate, you'll know exactly what to look for 📖✨