How IGI Certifies a Lab Grown Diamond After It Is Manufactured

After a lab grown diamond leaves the growth reactor, it has no grade, no identity, and no price. What happens next is a structured quality-control sequence run by the International Gemological Institute (IGI) that turns a rough or polished stone into a documented, traceable gem. IGI pioneered lab grown diamond grading in 2005 and today operates laboratories across more than 20 countries, making it the most experienced certification body in this specific category.

The process matters to buyers because the report is not a formality. It is the only independent record of what you are actually purchasing. Understanding each step helps you read that report with confidence rather than accepting it on faith.

What happens the moment a diamond arrives at an IGI laboratory?

The first thing IGI does is strip the stone of its commercial identity. Every diamond that enters the lab receives a unique, auto-generated identification number, and all owner information is masked from graders throughout the entire assessment. The stone is tracked electronically from that point forward, so central control always knows its location, but the gemologists examining it see only that number.

Between each grading stage, the diamond returns to central control and is reassigned to a different gemologist at random. That rotation is the core of IGI’s objectivity model: no single grader handles a stone from start to finish, which makes it structurally difficult for bias to creep in. The final report number that appears on your certificate is the same identification number assigned at intake.

How does IGI confirm the diamond is actually lab grown and not a simulant?

This is where the science gets specific. Before any quality grading begins, IGI runs advanced spectroscopic screening to confirm origin. Lab grown diamonds produced by Chemical Vapor Deposition (CVD) tend to show silicon-vacancy centers at around 738 nanometers under photoluminescence spectroscopy, while HPHT-grown stones display different defect signatures tied to their high-pressure growth environment. Natural diamonds and simulants like moissanite produce entirely different spectral profiles.

The growth method, CVD or HPHT, is then noted in the comments section of the report on request. For buyers, this matters because it answers a question that no visual inspection can: where did this carbon structure actually come from? Spectroscopy resolves that question with a precision that no jeweler’s loupe can match.

How are the 4Cs assessed, and what keeps the grades consistent?

Color and clarity are each graded by multiple independent gemologists working without knowledge of each other’s assessments. A final grade is only confirmed once those independent opinions reach consensus. For color, the stone is placed upside-down under standardized lighting and compared against master stones on the D-to-Z scale. For clarity, the gemologist works at 10x magnification, assessing the visibility, size, location, and nature of any internal or surface characteristics.

Cut grading for round brilliants goes further. IGI compares the stone’s overall proportions against its own research into brightness, fire, scintillation, and pattern. Polish and symmetry are assessed separately, and if either comes in below the level suggested by the proportions, the final cut grade is pulled down accordingly. Two stones with identical table percentages can therefore land on different cut grades based on finish quality alone.

Carat weight is measured on calibrated scales and recorded to the nearest hundredth of a carat. Millimeter measurements, covering diameter and depth, are also logged and appear on the report’s proportion diagram.

What is the laser inscription, and why does it matter?

Once grading is complete, IGI uses its LASERSCRIBE service to micro-inscribe the report number onto the diamond’s girdle, the narrow band running around the stone’s widest point. The inscription is invisible to the naked eye but readable under magnification. Every lab grown diamond IGI certifies receives this inscription as standard.

The practical value is straightforward: the inscription ties the physical stone to its specific report in IGI’s public database. If the girdle number and the report number match when you check IGI’s online verification tool, you have confirmation that the certificate was issued for that exact stone and not swapped in from somewhere else. No inscription match means no verified provenance, regardless of how official the paper looks.

IGI Certification Is What Separates a Diamond from a Documented Diamond

The manufacturing process, whether CVD or HPHT, produces a real diamond. The IGI certification process produces the evidence that the diamond is what it claims to be, graded honestly by people who never knew whose stone they were holding. Anonymous intake, multi-grader consensus on color and clarity, spectroscopic origin confirmation, and a laser-inscribed report number that ties to a public database: those four elements together are what give an IGI report its weight.

At Ouros Jewels, every lab grown diamond in the collection carries an IGI report for exactly this reason. If you want to see what a certified, graded stone looks like in a finished piece, the IGI Certified Round Lab Grown Diamond Stud Earrings are a good starting point.

Frequently Asked Questions

Does IGI certification apply to loose diamonds only, or also to finished jewelry?

IGI issues grading reports for both loose stones and finished jewelry. A jewelry report describes the piece as a whole, identifying all mounted gemstones, metal content, and purity stamps. For the center stone, shape, measurements, and 4Cs grades are provided to the extent the setting allows access.

Can I verify my IGI report number online without visiting a lab?

Yes. IGI maintains a public verification tool on its website where you enter the report number printed on your certificate. The result shows the full grading data on record for that number. If the data matches your physical report and the girdle inscription matches the number, the certificate is genuine.

Will the IGI report tell me whether my diamond was grown by CVD or HPHT?

It can. IGI notes the growth method in the comments section of the lab grown diamond report on request. The distinction is confirmed through spectroscopic testing during the origin verification stage, not through visual inspection, so the information is scientifically grounded rather than self-reported by the manufacturer.

Does IGI grade colored lab grown diamonds differently from colorless ones?

The 4Cs framework applies to both, but colored lab grown diamonds receive an additional assessment of color origin. Spectroscopic analysis confirms whether the color is a natural result of the growth process or the product of post-growth treatment such as irradiation or HPHT color enhancement. That distinction appears on the report.

Is a higher IGI cut grade always worth paying more for?

In most cases, yes, particularly for round brilliants. Cut is the one quality factor entirely controlled by the cutter after the rough stone exists, and IGI’s grading accounts for polish and symmetry as well as proportions. A poorly cut stone of higher carat weight will typically look smaller and less brilliant than a well-cut stone of lower weight, so the cut grade has a direct effect on how the diamond performs in light.