When you buy a lab-grown diamond, the certificate that accompanies it carries as much weight as the stone itself. It is the independent record of what you are paying for, assessed by a laboratory that has no stake in the sale. Two names appear most often on these reports: IGI and GIA. Both are widely recognised gemmological laboratories, and both grade lab-grown diamonds to a documented standard. The differences between them are real, but they are differences of approach and presentation rather than of trustworthiness. This guide explains how each laboratory grades a lab-grown diamond, how their reports differ, and what to check on the certificate before you commit.
Why independent certification matters
A lab-grown diamond is chemically, physically, and optically identical to a mined diamond. It is grown in a controlled environment rather than extracted from the earth, but the finished stone is a true diamond and is graded against the same criteria. The role of an independent laboratory is to assess that stone against those criteria without commercial influence, then issue a report that any buyer can verify.
Independent grading is what allows you to compare two stones with confidence. A carat weight, a colour grade, and a clarity grade only mean something when an accredited laboratory has assessed them to a consistent standard. At CRTD, every stone we source is independently certified by IGI, GIA, or an equivalent laboratory, and we hold a VS1 minimum on clarity. You can read more about our standards on our quality page.
Who are IGI and GIA?
The Gemological Institute of America (GIA) is a non-profit institute founded in 1931. It developed the 4Cs framework (cut, colour, clarity, and carat weight) and the international diamond grading scale that the wider industry now uses. GIA is regarded as a benchmark for consistency, particularly for white mined diamonds, and it began issuing reports for lab-grown diamonds as that market matured.
The International Gemological Institute (IGI), founded in 1975, is one of the largest gemmological laboratories in the world by volume. IGI built significant capacity for grading lab-grown diamonds early, and as a result the majority of lab-grown stones in the market today carry an IGI report. For lab-grown diamonds specifically, IGI is the laboratory you will encounter most often.
How each laboratory grades a lab-grown diamond
Both laboratories assess the same four characteristics: cut, colour, clarity, and carat weight. Both clearly identify the stone as laboratory-grown on the report, which is a requirement of fair disclosure. The grading is carried out by trained gemmologists using calibrated equipment, and both laboratories laser-inscribe a report number on the girdle of the stone so it can be matched to its certificate.
The practical distinctions are these:
- Grading scale presentation. GIA historically reported lab-grown colour and clarity using descriptive ranges, and now applies the same full grading scale it uses for mined diamonds. IGI reports colour and clarity using the familiar letter and grade designations on every report.
- Consistency and reputation. GIA is widely cited as the strictest and most consistent grader, a reputation built over decades on mined stones. IGI grading is robust and accredited; some buyers note that grading standards can appear marginally more generous, so comparing like for like matters.
- Volume and availability. Because IGI grades the larger share of lab-grown diamonds, you will find more IGI-certified stones across more cuts and carat weights. GIA reports are available but less common for lab-grown.
Neither approach makes a report unreliable. What matters is that you compare two stones graded by the same laboratory, because a small difference in grading style can otherwise make a fair comparison harder.
IGI vs GIA at a glance
| Consideration | IGI | GIA |
|---|---|---|
| Share of lab-grown market | Grades the majority of lab-grown diamonds in circulation | Smaller share for lab-grown; broader presence for mined stones |
| Grading style | Full letter and grade designations on every report; widely accredited | Regarded as the strictest and most consistent benchmark; full scale applied |
| Report contents | 4Cs, measurements, proportions, laboratory-grown disclosure, laser inscription, QR or online verification | 4Cs, measurements, proportions, laboratory-grown disclosure, laser inscription, online verification |
What to check on the report
Whichever laboratory graded the stone, read the report rather than only the headline grade. The details below tell you what you are actually buying.
- Laboratory-grown statement. A genuine report states clearly that the diamond is laboratory-grown. This is expected and correct; it is not a caveat.
- Report number and laser inscription. The number on the certificate should match the inscription on the diamond girdle. You can confirm it on the laboratory's own verification website.
- The 4Cs. Carat weight, colour grade, clarity grade, and cut grade. For our stones, clarity sits at VS1 or better.
- Measurements and proportions. Dimensions in millimetres, table and depth percentages, and symmetry and polish ratings, which influence how the stone returns light.
- Growth method, where noted. Some reports indicate whether the stone was grown by CVD or HPHT. This does not change the quality of a well-graded diamond, but it is useful information.
You can verify any report directly through the issuing laboratory using the report number, which is the single most reliable check available to a buyer.
So which certificate should you choose?
For a lab-grown diamond, both an IGI and a GIA report are sound foundations for a confident purchase. GIA carries the longer benchmark reputation for grading consistency, while IGI offers the widest selection of certified lab-grown stones across cuts and carat weights. The more useful habit is not to favour one laboratory in the abstract, but to compare stones graded by the same laboratory and to verify the report before you buy. A certified stone, read carefully and confirmed against its inscription, is a sound choice regardless of which of these two names appears at the top.
Frequently asked questions
Is an IGI certificate as good as a GIA certificate for a lab-grown diamond?
Both are accredited and trustworthy. GIA is often described as the stricter, more consistent grader, while IGI grades the larger share of lab-grown diamonds and offers wider availability. For a like-for-like comparison, compare stones graded by the same laboratory.
Does the certificate prove the diamond is real?
A lab-grown diamond is a real diamond, chemically and optically identical to a mined one. The report confirms the stone has been independently assessed for cut, colour, clarity, and carat weight, and states clearly that it is laboratory-grown.
How do I verify a report is genuine?
Use the report number printed on the certificate and the laser inscription on the diamond girdle, then check both against the issuing laboratory's online verification service. The number, the inscription, and the online record should all match.
Which certificate do CRTD diamonds carry?
Every stone we source is independently certified by IGI, GIA, or an equivalent laboratory, with a VS1 minimum on clarity. You can read about our sourcing approach on our how we source page.
Choose a certified stone with confidence
Certification is the foundation of a considered diamond purchase, and we hold every stone to it. Explore our independently certified lab-grown diamonds across the full range of cuts and carat weights in our complete collection, or learn more about the standards behind each stone on our quality page.