Lab Grown Diamond Certification: IGI vs GIA Explained

When it comes to lab-grown diamond certification, the conversation almost always narrows to two names: IGI and GIA. Both are respected. Both issue detailed reports. But they take meaningfully different paths to get there.

This guide walks through what each certificate actually says, how the laboratories compare, and how to read a report with confidence. The goal is clarity. Not a winner-takes-all verdict.

What Diamond Certification Actually Is

A diamond grading report is an independent, third-party assessment of a stone's characteristics, issued by a gemological laboratory after physical examination. The industry term "certification" is technically a misnomer. Laboratories issue grading reports, not certifications in the regulatory sense. But the words are used interchangeably in retail. And this guide follows that convention.

A grading report matters for four reasons. 

• Trust: an unbiased opinion separate from the seller.

• Transparency: every measurable trait disclosed in a standardised format.

• Insurance: most insurers require a report to set a replacement valuation.

• Resale: a recognised report is the common language of the secondary market.

For a lab-grown diamond, a report does one additional thing. It confirms the origin. The certificate explicitly states that the stone is laboratory-grown, distinguishing it from natural diamonds and from simulants like cubic zirconia.

The Major Gemological Laboratories

An Australian buyer will encounter three main laboratories when shopping for lab-grown diamonds. Two dominate the conversation. One offers a specialised alternative.

GIA - The Gemological Institute of America

Founded in 1931 by Robert M. Shipley, GIA is the institute that developed the 4Cs and the D-to-Z colour scale that the entire industry now uses. Headquartered in Carlsbad, California, it is widely regarded as the standard-setting authority on diamond grading. GIA first began issuing reports for lab-grown diamonds in 2007 and updated its terminology and report format on 1 July 2020, a milestone covered in detail later in this guide.

IGI - The International Gemological Institute

Founded in 1975 in Antwerp, Belgium, IGI operates the largest multi-city laboratory network in gemology, with sites across Antwerp, Mumbai, Surat, New York, Bangkok, Tokyo, Dubai, Hong Kong, and beyond. It is the laboratory that has come to dominate lab-grown diamond grading, largely because it began grading lab-grown stones earlier and at bigger scale than GIA. In 2023, global investment firm Blackstone bought a controlling majority stake in IGI in a deal valued at approximately USD 530 million. It was the largest single transaction in the gemological-laboratory sector on record. And a clear signal of the commercial weight the lab-grown market now carries.

Other Recognised Laboratories

GCAL, the Gem Certification & Assurance Lab, operates out of New York and is best known for its Certified 8X report, which layers optical light-performance metrics over standard 4C grading. GCAL is unique in offering a grading guarantee, backing its assessments with financial assurance. HRD Antwerp, the laboratory of the Antwerp World Diamond Centre, is more frequently encountered in continental Europe than in Australia. AGS, the American Gem Society Laboratories, was the historical US alternative to GIA, but its laboratory operations were acquired by GIA in 2022.

A note of caution: certificates issued by the retailer selling the stone are not third-party reports and should not be treated as such. For a lab-grown diamond of meaningful size, an IGI or GIA report is the minimum standard.

Why IGI Dominates the Lab-Grown Diamond Market

IGI sits at the centre of lab-grown grading for two interlocking reasons: timing and geography.

The laboratory moved into lab-grown certification early, beginning in 2005, and built dedicated lab-grown grading lines at scale. Its largest facilities in Mumbai and Surat sit geographically adjacent to the world's biggest lab-grown diamond production centres. GIA, by contrast, approached the category more cautiously, using the term "synthetic" in its early reports and issuing lower volumes.

As a result, the overwhelming majority of polished lab-grown stones in global inventory today carry IGI reports. Lab-grown diamonds currently account for approximately 55 to 60 per cent of IGI's revenue. The laboratory grades millions of lab-grown stones annually, a volume GIA has not matched. For better or worse, IGI is the practical standard for this category.

GIA's Lab-Grown Diamond Report - A Quiet Evolution

GIA's approach to lab-grown grading has evolved meaningfully over time. In 2007, the institute introduced the "GIA Synthetic Diamond Grading Report," which used descriptive colour and clarity ranges such as "Colourless" and "Very Slightly Included" rather than the granular letter-and-number grades used for natural diamonds.

On 1 July 2020, GIA made two significant changes. It replaced the word "synthetic" with "laboratory-grown." And it began issuing reports that use the identical D-to-Z colour scale and FL-to-I3 clarity scale as its natural diamond reports. This update was the moment IGI and GIA reports became visually and structurally comparable. The same grades, on the same scales, for the same stone.

Then, most recently, in June 2025, GIA announced another fundamental shift. The institute would stop using the traditional D-to-Z colour and FL-to-I3 clarity grading system for laboratory-grown diamonds, moving instead to a simplified two-tier quality assessment: "Premium" or "Standard." This change rolled out in October 2025. As a result, new GIA reports for lab-grown diamonds no longer carry the granular colour and clarity grades that buyers have traditionally used to compare stones. IGI, by contrast, continues to issue detailed 4Cs reports for lab-grown diamonds, maintaining the full colour and clarity scales.

IGI vs GIA - A Side-by-Side Comparison

The table below contrasts IGI and GIA across the criteria that matter most to a buyer. Note that from October 2025, GIA no longer issues traditional colour and clarity grades for lab-grown diamonds, instead using a simplified two-tier system.

Key takeaway for buyers: IGI continues to provide the traditional, detailed colour and clarity grading that the diamond industry has relied upon for decades. GIA has moved to a simplified "Premium or Standard" designation for lab-grown diamonds, offering less granular information. Buyers seeking the fullest possible transparency on a lab-grown diamond's characteristics should prioritise IGI certification.

How to Read a Lab-Grown Diamond Grading Report

A grading report contains more information than most buyers realise. Here is what every field means, whether on an IGI or GIA document.

Report number and date: A unique identifier and the date the report was issued. This number is also laser-inscribed on the diamond's girdle.

Shape and cutting style: Describes the outline (round, oval, emerald) and faceting pattern (brilliant, step cut).

Measurements: The diamond's dimensions in millimetres, usually given as length × width × depth.

Carat weight: The stone's weight, measured to two or three decimal places.

Colour grade: For IGI, a letter from E (colourless) to Z (noticeable colour). GIA reports issued from October 2025 no longer include a granular colour grade, instead assigning a simplified quality designation of "Premium" or "Standard."

Clarity grade: For IGI, a grade from FL (Flawless) to I3 (Included 3), assessed under 10x magnification. GIA reports issued from October 2025 no longer include a traditional clarity grade, as the institute has moved to its two-tier "Premium or Standard" system for laboratory-grown diamonds.

Cut grade (where given): An overall assessment of how well the diamond interacts with light, ranging from Excellent to Poor. GIA provides this only for standard round brilliants. IGI provides it for most shapes.

Polish and symmetry: Sub-grades assessing the finish of the diamond's facets, typically Excellent, Very Good, Good, Fair, or Poor.

Fluorescence: The diamond's reaction to ultraviolet light, graded as None, Faint, Medium, Strong, or Very Strong.

Proportions diagram: A visual representation of the diamond's facet angles and percentages.

Clarity plot: A top-down and bottom-up diagram of the diamond marked with symbols representing each inclusion. Red symbols indicate inclusions. Green symbols indicate blemishes.

Inscription: The laser-etched report number on the diamond's girdle, visible only under magnification. Both laboratories also inscribe wording identifying the stone as laboratory-grown.

Comments section: Where growth method (HPHT or CVD) and any post-growth treatments are disclosed.

Origin identification: A clear statement that the diamond is laboratory-grown.

Both laboratories' reports can be verified online by entering the report number into the laboratory's verification portal. Any seller unable to point to a working verification result should be treated with caution.

Grading Strictness - Is IGI Really Softer Than GIA?

A persistent perception in the diamond trade is that IGI grades more leniently than GIA, particularly in colour. The claim deserves examination.

Comparative regrading analyses have found that IGI colour grades on lab-grown stones tend to run approximately one to two grades more liberally than GIA equivalents when the same stones are submitted to both laboratories. A diamond graded as G colour by IGI might receive an H or I colour grade from GIA.

But nuance is essential. Any single stone may grade differently between laboratories, regardless of which is "stricter." Both apply the identical scales. And a meaningful proportion of reported divergence reflects the inherent subjectivity of grading borderline stones. Human gemologists, even well-trained ones, can disagree.

The practical implication for buyers is straightforward. Compare like with like. IGI with IGI. GIA with GIA. Do not assume a fixed cross-laboratory discount and treat any claim of "GIA-equivalent" with healthy scepticism.

Cut Grading - Where the Two Reports Genuinely Differ

This is a meaningful structural difference worth highlighting. GIA's cut grade is currently applied primarily to standard round brilliant diamonds. Fancy shapes such as oval, pear, cushion, emerald, and marquise typically do not receive an overall cut grade on a GIA report. Only polish and symmetry are provided.

IGI, by contrast, issues a full cut grade across most shapes. For buyers shopping for fancy cuts who want a single, comparable cut benchmark, IGI provides one additional data point that GIA does not.

But the situation is changing soon. In June 2026, GIA announced that it will introduce cut grades for fancy shapes beginning in 2027. The initial rollout will cover marquise, oval and pear-shaped diamonds, with the institute stating that it has been working toward cut-grade standards for fancy shapes since introducing its round brilliant cut-grading system in 2006. The move responds to long-standing industry demand, as cut quality can vary significantly across fancy shapes, and addresses the need for greater consumer protection.

GIA plans to share additional details about the launch and related laboratory services in early 2027. For now, IGI remains the laboratory offering full cut grading across the widest range of shapes. Once GIA's system is in place, buyers will have more comparable data across both laboratories for the three shapes initially covered. For round brilliants, the two reports are directly comparable. For fancy shapes, IGI currently offers a more complete picture, though this will evolve as GIA's new system rolls out.

Growth Method, Treatments, and What the Report Discloses

Both IGI and GIA disclose the growth method used to create the diamond: High Pressure High Temperature (HPHT) or Chemical Vapour Deposition (CVD). This information appears in the comments section of the report.

Many CVD-grown stones undergo a secondary HPHT process to improve colour. This is standard, accepted practice in the lab-grown industry. Reputable laboratories note it in the comments field. Disclosed post-growth treatments are not a flaw. They are a marker of transparency. The red flag is when treatments are not disclosed at all.

A well-disclosed report tells the complete story of the diamond, from seed to finished stone.

Common Myths About IGI and GIA Certification

IGI is not a real gemmological laboratory. False. IGI is a recognised international gemmological laboratory founded in 1975, with the largest multi-city network in gemology and the largest share of lab-grown diamond reports in the industry. It is not a lesser or unofficial laboratory.

GIA does not grade lab-grown diamonds. Incorrect. GIA has graded lab-grown diamonds since 2007 and has used the identical D-Z and FL-I3 grading scales as natural diamonds since 1 July 2020.

GIA-certified lab diamonds always have higher resale value. Not necessarily. Resale value for any diamond, lab-grown or natural, is driven primarily by the stone itself and market conditions, not solely by which of the two major laboratories graded it.

IGI is always a step softer than GIA. This claim does not survive close inspection. Stone-by-stone variation occurs in both directions. Broad generalisations rarely apply to a specific report.

Practical Guidance for Buyers

What to look for on a certificate: a report number that returns a match on the laboratory's online verification portal. The words "Laboratory Grown" or "Laboratory-Grown" are clearly present. A complete 4Cs picture. A clarity plot. Full disclosure of growth method and treatments.

The red flags: in-house certificates from the retailer. Photocopied reports. Missing report numbers. Any report that cannot be verified online.

When might one laboratory be preferable? IGI is the practical default for most lab-grown purchases. It offers abundant inventory, faster turnaround, and full cut grading across shapes. GIA is preferred by buyers who want the benchmark name on the report, who are comparing directly against natural diamond reports, or who are prioritising the strictest reading of the grading scales. Either is a valid choice when verified.

Conclusion

The conversation around lab-grown diamond certification is no longer about whether IGI or GIA is "real." Both are real. Both are credible. And both issue reports are worth trusting. The question is understanding what each report actually says, how to read it, and how to verify it.

A grading report is the quiet contract between a buyer and a stone. It documents the diamond's qualities in a standardised language that travels across jewellers, insurers, and eventually, the secondary market. The most beautiful diamond is, in the end, a known one.

FAQs on Lab-Grown Diamond Certification

Is IGI as good as GIA for lab-grown diamonds?

For lab-grown diamonds, IGI continues to use the traditional D-Z colour and FL-I3 clarity scales, while GIA moved to a simplified "Premium or Standard" quality assessment system from October 2025. Both laboratories disclose growth method and treatments, and both laser-inscribe the stone. GIA carries the older reputation as the strictest grader on historical reports, while IGI carries the largest share of lab-grown reports in the market today. Both are credible, but buyers seeking detailed colour and clarity grades should prioritise IGI.

Which certification is best for a lab-grown diamond?

There is no single best certification. Only the best certification for a given priority. IGI is the practical default given the volume of lab-grown stones it grades and its full cut grading across fancy shapes. GIA remains a respected name, but its post-October 2025 reports no longer offer the granular colour and clarity grades that buyers comparing against natural diamond benchmarks would expect. Both are accepted by jewellers and insurers.

Does GIA grade lab-grown diamonds?

Yes. GIA has graded lab-grown diamonds since 2007. On 1 July 2020, it updated its Laboratory-Grown Diamond Report to use the same colour and clarity nomenclature as natural diamonds. However, from October 2025, GIA moved to a simplified two-tier system for lab-grown diamonds, classifying stones as "Premium" or "Standard" instead of issuing traditional D-Z colour and FL-I3 clarity grades.

Is IGI stricter or softer than GIA?

A common trade perception is that IGI grades more leniently than GIA, particularly in colour. Comparative analyses have found IGI colour grades running roughly one to two grades more liberally on equivalent stones. That said, stone-by-stone variation occurs in both directions. For historical reports, both laboratories applied the same scales. For new GIA reports issued from October 2025, direct comparison is no longer possible because GIA no longer issues traditional colour and clarity grades.

How is a lab-grown diamond certificate verified?

Every IGI and GIA report carries a unique report number, which is also laser-inscribed on the diamond's girdle. The number can be entered into the IGI Report Check or GIA Report Check on the respective laboratory's website to confirm that the grading details match the physical stone.

Are HPHT and CVD diamonds disclosed on a grading report?

Yes. Both IGI and GIA disclose the growth method in the comments section of the report. Any post-growth treatments, such as HPHT colour improvement of CVD stones, are disclosed as well.

Do lab-grown diamonds need a certificate?

Any lab-grown diamond intended for fine jewellery, particularly engagement rings or stones above 0.50 carats, should carry an independent third-party report from IGI, GIA, or another recognised laboratory. Smaller accent stones may be sold uncertified within a piece, but the centre stone should always be documented.

What is the difference between IGI and GIA inscriptions?

Both laboratories laser-inscribe the report number onto the diamond's girdle along with wording identifying the stone as laboratory-grown. The inscription is microscopic, visible only under magnification, and serves as a permanent link between the physical stone and its report.