Diamond and moissanite certification: GRC, IGI, GIA explained
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Every stone we sell comes with a certificate. For moissanite that's GRC. For lab grown diamonds, IGI. Different gem types, different labs, and the certificates carry different weight in the market.
Here's what each certificate actually tells you, why we use the labs we use, and what to look out for when you're shopping for certified stones elsewhere.
Why certification matters
A certificate is an independent assessment of what a stone actually is. It confirms the type of stone, its specifications (cut, colour, clarity, carat), and in some cases its origin. Without it, you're relying entirely on the jeweller's word.
Certification lets you compare stones across different jewellers on a like-for-like basis. A 1 carat round F-VS1 lab grown diamond with an IGI certificate from one seller is directly comparable to the same specs from another seller. Without certification, those comparisons fall apart.
Certification also protects you on resale, insurance, and any future questions about authenticity.
IGI: lab grown diamonds
The International Gemological Institute (IGI) is the dominant grading lab for lab grown diamonds. They grade roughly 80% of the lab diamonds in the global market.
An IGI report for a lab grown diamond includes:
- Shape and cutting style
- Measurements (length, width, depth)
- Carat weight
- Cut grade (for round brilliants)
- Colour grade (D to Z)
- Clarity grade (FL to I3)
- Polish and symmetry grades
- Fluorescence
- Inclusion plot (diagram of where any inclusions are)
- Growth method (HPHT or CVD)
- A unique report number, often laser-inscribed on the stone
You can verify any IGI certificate by entering the report number at igi.org. The official record should match what you've been shown exactly.
GIA: natural diamonds (and increasingly lab grown)
The Gemological Institute of America (GIA) is the historical gold standard for natural diamond grading. They've graded the world's most famous diamonds and their methodology is the basis for the diamond grading systems used worldwide.
GIA only started grading lab grown diamonds in recent years. Their lab grown reports are generally considered slightly stricter than IGI's, but the difference is small. Both labs use the same scales.
For natural diamonds, GIA is the most trusted certification. For lab grown diamonds, both GIA and IGI are valid, but IGI is more common.
GRC: moissanite
The Gemological Research Center (GRC) is the main certifying body for moissanite stones. Different gem, different lab, but the same idea: independent confirmation of specifications.
A GRC report for a moissanite includes:
- Stone identification (silicon carbide, moissanite)
- Shape and cutting style
- Measurements
- Carat weight
- Colour grade
- Clarity grade
- Hardness rating (typically 9.25 on Mohs scale)
- Refractive index
GRC certification is the industry standard for moissanite. Worth noting that moissanite grading is generally simpler than diamond grading because lab grown moissanite is produced to very consistent specifications. The colour and clarity range is narrower than natural-or-lab diamond, so a typical GRC certificate will show high grades across the board.
What we use
Every lab grown diamond we sell comes with an IGI certificate. Every moissanite comes with a GRC certificate. The certificates are sent to you with the ring.
For natural diamonds (which we don't actively sell but can source on request), we use GIA-certified stones.
What about other labs?
You'll come across other certifications in the market. A few worth knowing about:
AGS (American Gem Society). Reputable lab with a slightly different cut grading scale. Their certificates are credible. AGS was acquired by GIA in 2022 and is being merged into GIA's operations.
EGL (European Gemological Laboratory). Multiple branches with varying standards. EGL USA in particular has had a reputation for grading more loosely than GIA or IGI. An EGL-certified stone may grade two to three steps lower under a GIA or IGI assessment. Worth being cautious if you're comparing prices across labs.
HRD (Hoge Raad voor Diamant). Belgian lab, well-regarded in Europe, equivalent rigor to GIA for most purposes.
In-house certificates. Some jewellers provide their own "appraisal" rather than independent certification. These are not the same thing. An appraisal from the seller of the stone is essentially the seller telling you what they're selling. It's better than nothing, but it's not third-party verification.
Red flags when shopping certified stones
A few things to watch for:
The price is significantly cheaper than equivalent IGI/GIA stones. Either the certification is from a more lenient lab, or something's off. Worth asking direct questions.
The jeweller won't show you the certificate before purchase. Every reputable jeweller should be able to send you the certificate ahead of any commitment.
The certificate is for a different stone than what you're being shown. Rare but it happens. The laser inscription should match the report number on the certificate. Ask to verify.
The certificate is several years old. Stones can be damaged or recut over time. For a significant purchase, the certificate should be reasonably recent (within the last year or two).
Insurance and resale
You'll need a certificate to insure the ring properly. Most insurance providers require it. Keep the certificate somewhere safe (and ideally scan it to keep a digital copy).
For resale or future appraisal, the certificate is the document that establishes what the stone is. Without it, any future buyer will have to certify it themselves, which costs $100-300.
The bottom line
Buy certified. For lab grown diamonds, look for IGI or GIA. For moissanite, look for GRC. For natural diamonds, GIA is the gold standard.
If a stone is being sold without independent certification, or only with an in-house appraisal, walk away or ask for proper certification before committing.
If you want to talk through certified stones in person or have me interpret a certificate you've been shown by another jeweller, that's part of what we do in a free consultation.