When you shop for a lab-grown diamond, you will see the words "IGI certified" again and again. An IGI certificate – properly called an IGI diamond grading report – is an independent, expert record of exactly what your diamond is. This guide explains who IGI is, what every line on an IGI lab-grown diamond report means, and how to check that a certificate is genuine.
What is IGI?
IGI stands for the International Gemological Institute. Founded in Antwerp, Belgium in 1975, it is one of the largest independent gem-grading laboratories in the world, with laboratories in major diamond centres. IGI grades both natural and laboratory-grown diamonds, and it is one of the most widely used laboratories for lab-grown diamonds.
Because IGI is independent, it has no interest in making your diamond sound better than it is. That is why a grading report is so valuable: it lets you compare diamonds on facts, not sales talk.
IGI vs GIA: which is better?
The Gemological Institute of America (GIA) and IGI are both respected laboratories, and both grade lab-grown diamonds using the same colour and clarity scales they use for natural stones. GIA is best known for natural diamonds; IGI has graded a very large share of the world's lab-grown diamonds. For a lab-grown engagement ring, an IGI report is a trusted, industry-standard choice.
How to read an IGI lab-grown diamond report, line by line
Here is what you will find on a typical IGI Laboratory Grown Diamond Report, and what each item means for you:
- Report number – a unique ID. On IGI lab-grown reports it begins with "LG", for laboratory grown. You use this number to verify the report online.
- Description – states "Laboratory Grown Diamond", so the origin is never in doubt.
- Shape and cutting style – for example round brilliant, oval brilliant, or "cut cornered rectangular modified brilliant" (a radiant cut).
- Measurements – the diamond's length, width and depth in millimetres. Two diamonds of the same carat can face up at different sizes, so this matters.
- Carat weight – the diamond's weight. One carat equals 0.2 grams.
- Colour grade – on the D-to-Z scale, where D is completely colourless. D, E and F are "colourless"; G to J are "near colourless".
- Clarity grade – how free the diamond is of inclusions and blemishes, from FL (flawless) through IF, VVS1, VVS2, VS1, VS2, SI1, SI2 to I1–I3.
- Cut grade – for round brilliants, how well the diamond is proportioned to return light (for example Ideal or Excellent). Cut has the biggest influence on sparkle.
- Polish and symmetry – the quality of the finish and the precision of the facets. Look for Excellent or Very Good.
- Fluorescence – whether the diamond glows under ultraviolet light. "None" is common in lab-grown diamonds.
- Inscription(s) – the microscopic laser inscription on the diamond's girdle, usually "LABGROWN IGI" followed by the report number. A jeweller can show it to you under magnification, matching the stone to its report.
- Comments – often "As Grown – No indication of post-growth treatment", plus the growth method: HPHT (High Pressure High Temperature) or CVD (Chemical Vapour Deposition). Some CVD diamonds are treated after growth to improve colour; the report will say so.
- Proportions diagram – table %, depth %, crown and pavilion angles and girdle thickness, for anyone who wants the technical detail.
How to verify an IGI certificate
- Find the report number (starting with "LG" for lab-grown) on your certificate.
- Enter it in the report verification tool on IGI's official website, igi.org.
- Check that the online details – shape, measurements, carat, colour and clarity – match your paper or digital report exactly.
- Ask your jeweller to show you the laser inscription on the girdle under magnification, and confirm it matches the report number.
What IGI grades give the best value?
For a lab-grown engagement ring, many buyers find the sweet spot is:
- Colour: D to G – white and bright in any metal.
- Clarity: VS2 or better – inclusions are not visible to the naked eye.
- Cut: Ideal or Excellent for round diamonds; Excellent polish and symmetry for fancy shapes.
Learn more in our guide to the 4Cs of diamonds.
Certified lab-grown diamonds at House of Honcho💎
Our centre diamonds are certified lab-grown diamonds, graded by IGI or GIA depending on the stone, and every piece comes with a certificate of authenticity. Browse our certified lab-grown diamond engagement rings, our IGI certified lab diamond tennis bracelets and our wedding bands. New to lab diamonds? Start with Lab-Grown vs Natural Diamonds: Are They the Same?
Frequently asked questions
Is an IGI certificate the same as an appraisal?
No. An IGI report grades the diamond's characteristics. It does not state a dollar value. An appraisal or valuation (often used for insurance) is a separate document.
Does IGI grade natural diamonds too?
Yes. IGI grades natural diamonds, lab-grown diamonds and other gemstones. Natural diamond reports are clearly different from lab-grown reports.
What does "As Grown" mean on an IGI report?
It means the laboratory found no indication that the diamond's colour was improved by treatment after it was grown.
Is HPHT or CVD better?
Neither is automatically better. Both produce real diamond. Judge each stone on its own grades – colour, clarity and cut – rather than the growth method.
Can a certificate be faked?
Anything can be imitated, which is why you should always verify the report number on IGI's website and check the girdle inscription matches.
Image credits: polished diamonds by Bilovitskiy (CC BY 4.0, via Wikimedia Commons); lab-grown CVD diamond by Steve Jurvetson (CC BY 2.0, via Wikimedia Commons). Ring photo: House of Honcho💎.
