A diamond certificate is your diamond’s ID card. It tells you what the stone is, how it was graded, and how to compare it fairly.

This guide explains how to read an IGI or GIA diamond report, step by step, without jargon.

What is an IGI or GIA report?

An IGI or GIA report is an independent grading document issued by a gemological laboratory.

It describes a diamond’s measurable and visible characteristics, including the diamond's 4c's cut, color, clarity, carat - as well as  proportions, and other identifying details. The report does not assign value or price. Its purpose is transparency and comparability.

At Carateu, every diamond is independently certified before it is listed.

1. Certificate number

Every report has a unique certificate number.

This number allows you to:

• Verify the report directly with the lab
• Match the report to the correct diamond
• Search for the diamond online

Tip: The certificate number is usually laser-inscribed on the diamond’s girdle and can be seen under magnification.

2. Shape and cutting style

This tells you the diamond’s outline and facet pattern.

Examples:

• Shape: Round, Oval, Emerald, Radiant, Cushion
• Cutting style: Brilliant, Step cut, Mixed cut

The shape affects visual style. The cutting style affects how the diamond handles light.

3. Carat weight

Carat refers to weight, not size.

Two diamonds with the same carat weight can look different in size depending on:

• Shape
• Depth
• Proportions

This is why measurements matter.

4. Measurements

Measurements show the diamond’s dimensions in millimeters.

For example:

• Round: 6.45–6.48 × 3.95 mm
• Fancy shapes: Length × width × depth

These numbers help you understand:

• How large the diamond looks face-up
• Whether the proportions are balanced for the shape

5. Cut (or polish and symmetry)

For round diamonds, the report includes a cut grade (Excellent to Poor).

For fancy shapes, cut quality is reflected through:

• Polish
• Symmetry
• Proportions

Cut quality has the biggest impact on sparkle and brilliance.

6. Color grade

Color grades describe how colorless a diamond appears.

The scale runs from:

• D (colorless)
• To Z (visible yellow or brown tint)

A lower letter does not mean a bad diamond. Many diamonds appear white to the eye even if they are not in the top color range.

7. Clarity grade

Clarity describes internal characteristics (inclusions) and surface features (blemishes).

Common grades:

• FL / IF
• VVS1 / VVS2
• VS1 / VS2
• SI1 / SI2

Most VS and many SI diamonds are eye-clean, meaning inclusions are not visible without magnification.

8. Clarity diagram

The diagram shows where inclusions are located inside the diamond.

Important things to look for:

• Inclusions near the center vs the edge
• Large dark inclusions
• Multiple inclusions grouped together

Location often matters more than the grade itself.

9. Polish and symmetry

These grades describe how precisely the diamond was finished.

• Polish: Surface quality
• Symmetry: Alignment of facets

Excellent or Very Good grades are ideal for most buyers.

10. Fluorescence

Fluorescence describes how a diamond reacts to UV light.

Most diamonds show:

• None or Faint fluorescence

This is generally preferred, but moderate fluorescence is not automatically bad. Context matters.

11. Lab grown or natural origin

The report clearly states whether the diamond is:

• Natural
• Lab grown

For lab grown diamonds, the report also lists the growth method.

This ensures full transparency.

IGI vs GIA: what’s the difference?

Both IGI and GIA are respected gemological laboratories.

In simple terms:

• GIA is often considered stricter for natural diamonds
• IGI is widely used and trusted for lab grown diamonds

What matters most is not the lab name alone, but how the diamond looks and how its proportions, cut quality, and clarity work together.

Final tip: use the report as a tool, not a verdict

A certificate does not tell you if a diamond is beautiful.
It gives you the information needed to compare diamonds fairly.

Always combine the report with:

• High-quality video
• Proportion analysis
• Visual inspection

If you would like help reading a specific report, you are always welcome to contact Carateu.

Ready to check a diamond?
Use our Diamond Search to look up a diamond by its IGI or GIA certificate number.

Frequently Asked Questions about IGI and GIA Diamond Reports

Is an IGI or GIA diamond report real?

Yes. Both IGI and GIA are independent gemological laboratories that issue diamond grading reports based on standardized criteria. Their reports are widely used in the global diamond industry.

Is GIA better than IGI?

GIA is often considered stricter, particularly for natural diamonds. IGI is widely trusted and commonly used for lab grown diamonds. What matters most is not the lab alone, but the diamond’s cut quality, proportions, and how it looks in real life.

Can I trust an IGI certificate for a lab grown diamond?

Yes. IGI is the most common and widely accepted certification lab for lab grown diamonds, especially in Europe. IGI reports clearly state the diamond’s origin and grading details.

Does a diamond certificate show the price or value?

No. A diamond report does not include price or value. It only describes the diamond’s characteristics so stones can be compared fairly.

Is the certificate number engraved on the diamond?

In most cases, yes. The certificate number is usually laser-inscribed on the diamond’s girdle and can be seen under magnification.

Why do two diamonds with the same grades look different?

Diamonds with identical grades can still look different due to proportions, facet alignment, inclusion placement, and overall cut quality. This is why video and visual inspection matter alongside the report.

Can I look up a diamond using its certificate number?

Yes. You can use the certificate number to search for a matching diamond on Carateu and verify its details before purchase.