How to Read an IGI Lab-Grown Diamond Report

An IGI lab-grown diamond report contains far more than a collection of grades. It confirms that the stone is a laboratory-grown diamond, records its dimensions and quality characteristics, and provides information that can help you compare it with other diamonds.

Understanding the report has become particularly important following GIA’s changes to lab-grown diamond grading. Since October 2025, GIA has classified eligible colourless and near-colourless lab-grown diamonds as either Premium or Standard, rather than assigning the precise colour and clarity grades traditionally used for natural diamonds. IGI, meanwhile, has reaffirmed its commitment to providing full 4Cs grading for both natural and lab-grown diamonds.

This means an IGI report can give buyers more granular information when comparing individual lab-grown diamonds. However, no grading report can tell you everything about how attractive a diamond will look. You still need to evaluate cut precision, transparency, tint and light performance before making a purchase.

Key Takeaways

• IGI reports identify the diamond as laboratory-grown and provide detailed 4Cs grades.
• Check that the report number matches the laser inscription on the diamond.
• Cut quality should usually be prioritised above extremely high colour or clarity grades.
• Growth method and post-growth treatments may appear in the comments section.
• GIA now uses broader Premium and Standard classifications for eligible lab-grown diamonds.
• An IGI report is useful, but images, videos and light-performance analysis are still important.

For a broader introduction, read our guide to lab-grown diamond certification.

What Is an IGI Lab-Grown Diamond Report?

An IGI Laboratory Grown Diamond Report is an independent assessment produced by the International Gemological Institute. IGI began grading lab-grown diamonds in 2005 and has become one of the most widely used laboratories within the lab-grown diamond market.

The report normally includes:

• Confirmation that the diamond is laboratory-grown
• The report number
• Shape and cutting style
• Measurements
• Carat weight
• Colour grade
• Clarity grade
• Cut grade, where applicable
• Polish
• Symmetry
• Fluorescence
• Proportion information
• Comments about growth method or treatments
• A clarity-characteristics diagram on some reports

Technically, this is a grading report rather than a guarantee of value. The term “IGI certificate” is commonly used by retailers and shoppers, but the document describes the diamond’s assessed characteristics. It does not establish a retail price or guarantee that the diamond is beautiful.

You can learn more about the laboratory in our dedicated IGI lab diamond certification guide.

How to Read an IGI Lab-Grown Diamond Report Step by Step

1. Report Number

Every IGI report has a unique report number. This number connects the physical diamond to its digital grading information.

Enter the number into IGI’s online report-verification service before buying. This allows you to confirm that the report exists and that the information shown by the retailer matches IGI’s records.

The same number is commonly laser-inscribed on the diamond’s girdle. Ask the retailer to confirm that the inscription has been checked before shipping.

A laser inscription is extremely small and normally requires magnification to read. It should not affect the appearance of the diamond.

2. Description and Laboratory-Grown Identification

The report should clearly identify the stone as a laboratory-grown diamond.

This is one of the most important parts of the document. Lab-grown diamonds have essentially the same fundamental chemical and physical characteristics as natural diamonds, but they are created in a controlled manufacturing environment rather than formed underground.

Do not confuse a laboratory-grown diamond with a diamond simulant. Cubic zirconia and moissanite may resemble diamonds, but they are different materials. An IGI report confirms that the graded stone is a diamond and identifies its laboratory-grown origin.

3. Growth Process and Treatments

Lab-grown diamonds are primarily produced using one of two methods:

• Chemical Vapour Deposition, or CVD
• High Pressure High Temperature, or HPHT

The growth process, along with the presence of post-growth treatments, may be disclosed within the report’s comments. IGI states that the growth process and treatments can be noted upon request.

A treatment is not automatically a reason to reject a diamond. HPHT treatment, for example, may be used to improve the colour of a CVD-grown diamond. The important point is transparency.

Growth method alone does not determine whether a diamond is attractive. Both processes can produce excellent diamonds, while both can also produce stones with tint, strain, haziness or other visual issues.

Our HPHT vs CVD lab diamonds guide explains the differences in more detail.

4. Shape and Cutting Style

This section describes the diamond’s outline and facet arrangement.

Common examples include:

• Round brilliant
• Oval brilliant
• Cushion modified brilliant
• Emerald cut
• Pear brilliant
• Radiant cut
• Princess cut

Shape and cutting style are related, but they are not the same thing. “Oval” describes the outline, while “oval brilliant” describes how the facets have been arranged.

Modified brilliant cuts may contain additional facets. This is common in cushions, radiants and some other fancy shapes. The wording does not necessarily indicate higher or lower quality.

5. Measurements

The measurements describe the physical dimensions of the diamond in millimetres.

A round diamond may be shown in a format such as:

7.10 × 7.14 × 4.32 mm

The first two figures represent the minimum and maximum diameter. The final figure represents depth.

Fancy-shaped diamonds are normally listed as:

Length × width × depth

Measurements help you understand how large the diamond will appear. Two diamonds with the same carat weight can face up very differently depending on their proportions.

For elongated shapes, divide the length by the width to calculate the length-to-width ratio. For example:

10.00 ÷ 7.00 = 1.43

Whether that ratio is desirable depends on the shape and your personal preference. Some buyers prefer a longer oval or radiant, while others prefer a rounder outline.

6. Carat Weight

Carat is a measure of weight, not a direct measurement of visible size. One carat equals 200 milligrams.

1.01 ct D VVS1 Round Cut Precision Lab Grown Diamond from Whiteflash

A heavier diamond does not always look larger. A poorly proportioned diamond may carry excessive weight in its depth, causing it to appear smaller from above than a lighter, better-proportioned stone.

Always compare carat weight with:

• Face-up measurements
• Total depth
• Shape
• Cut quality
• Visual appearance

Our diamond size guide provides examples of how different carat weights can appear.

7. Colour Grade

IGI continues to grade colourless and near-colourless lab-grown diamonds using the familiar D-to-Z colour scale.

• D to F: Colourless
• G to J: Near-colourless
• K to M: Slightly tinted
• N and below: Increasingly noticeable colour

IGI grades colour in a controlled viewing environment, with multiple graders independently assessing the diamond.

A higher colour grade does not automatically make a diamond more beautiful. Many G or H lab-grown diamonds appear colourless once set, particularly in smaller sizes and round brilliant cuts.

The type of colour also matters. Some lab-grown diamonds display grey, brown or blue nuance that may not be fully communicated by the letter grade. Review a high-quality video rather than relying only on the report.

Read our full guide to lab-grown diamond colour before deciding how high you need to go.

8. Clarity Grade

Clarity describes inclusions inside the diamond and blemishes on its surface. IGI evaluates clarity under 10× magnification.

The principal grades are:

• FL: Flawless
• IF: Internally Flawless
• VVS1 and VVS2: Very, Very Slightly Included
• VS1 and VS2: Very Slightly Included
• SI1 and SI2: Slightly Included
• I1, I2 and I3: Included

Most buyers do not need an IF or VVS lab-grown diamond. A well-chosen VS1 or VS2 diamond will often be completely eye-clean and can offer better value.

However, the location and nature of the inclusions matter. Watch for:

• Dark inclusions beneath the table
• Large inclusions near the centre
• Clouds that reduce transparency
• Inclusions extending to the surface
• Feathers close to vulnerable corners
• Features that may interfere with light performance

A clarity grade does not always capture wider crystal-quality issues such as strain or haziness. This is why video inspection remains important.

9. Cut Grade

Cut quality has the greatest influence on a diamond’s brightness, fire and sparkle.

For round brilliant diamonds, IGI assesses how the proportions and facet relationships contribute to brightness, fire, scintillation and pattern. IGI also uses a shape-specific assessment system for fancy-shaped diamonds.

Do not assume that every diamond labelled “Excellent” or “Ideal” will perform identically. These grades cover a range of proportions, and two diamonds with the same grade may display noticeably different levels of light return and optical symmetry.

For round diamonds, examine:

• Table percentage
• Total depth
• Crown angle
• Pavilion angle
• Girdle thickness
• Optical symmetry
• Light leakage

For fancy shapes, also consider shape-specific problems such as:

• Bow ties in ovals, pears and marquises
• Dark centres in poorly cut emerald cuts
• Uneven brightness in cushions
• Windowing or weak contrast patterns

Our lab diamond cut guide explains why the grade on the report is only the beginning of a proper cut assessment.