IGI Certification Explained: How to Read a Lab-Grown Diamond Report
When you choose a lab-grown diamond for your engagement ring, the certificate that comes with it is just as important as the stone itself. It is an independent, expert description of exactly what you are buying. At LM Jewellers, our loose lab-grown diamonds come with IGI certification — so here is how to read one with confidence.
What is the IGI?
The International Gemological Institute is one of the world’s largest independent gem-grading laboratories, founded in Antwerp in 1975. Today it grades a large share of the world’s lab-grown diamonds. Crucially, IGI does not sell diamonds: its role is to measure and describe them objectively, so that a 1.00ct, G colour, VS2 diamond means the same thing wherever you buy it.
The anatomy of a report
Report number
Every report has a unique number. On most IGI-graded diamonds this number is also laser-inscribed on the girdle (the thin outer edge of the stone) — invisible to the naked eye, but visible under magnification. It links your physical diamond to its paperwork.
Shape and cutting style
For example “Round Brilliant”, “Oval Brilliant” or “Emerald Step Cut”. Not sure which you prefer? Our guide to diamond shapes walks through each one.
Measurements
Length, width and depth in millimetres. Two diamonds of the same carat weight can look quite different in size depending on how they are cut — measurements tell you how large the stone will actually look on the hand.
The 4Cs
| Grade | What it measures | What to look for |
|---|---|---|
| Carat | Weight, not size (1 carat = 0.2 g) | Choose with the measurements, not the number alone |
| Colour | How colourless the stone is, from D (colourless) downwards | D–F is icy white; G–H looks white to the eye, especially in yellow gold |
| Clarity | Tiny internal features and surface marks | VS2 and above is typically “eye-clean” |
| Cut | Proportions, symmetry and polish (graded on round brilliants) | Excellent or Ideal for maximum sparkle |
Polish and symmetry
How smooth the facets are and how precisely they line up. “Excellent” or “Very Good” is what you want.
Fluorescence
Whether the diamond glows under UV light. In most cases this has no visible effect in daylight.
Growth method
IGI states that the diamond is laboratory-grown and usually notes the method — CVD (chemical vapour deposition) or HPHT (high pressure, high temperature). Both produce real diamond: the same carbon crystal, the same hardness and the same fire as a mined stone. Some reports also note “post-growth treatment”, a common process used to improve colour; it is permanent and is disclosed so you have the full picture.
A lab-grown diamond is a real diamond. The report proves exactly which one is yours.
How to verify your report
- Visit the IGI website and open the report verification page.
- Enter the report number printed on your certificate.
- Check that the shape, measurements and grades match your paperwork.
It takes less than a minute, and it is something we encourage every client to do.
Choosing your diamond with us
When you build a ring with LM Jewellers, you can compare certified lab-grown diamonds side by side and choose by the grades that matter most to you. If you would like a second opinion on a report, we’re happy to talk you through it during a private consultation.