You have found the ring you love and the diamond looks beautiful. Then someone hands you a grading report covered in letters, numbers and diagrams. What does it actually tell you, and does it matter whether it comes from IGI or GIA? After around 25 years in the diamond trade, our honest answer is that a grading report is one of the most useful tools you have when buying a diamond, as long as you know how to read it.
What a diamond grading report is (and isn't)
A grading report, often called a certificate, is an independent laboratory's assessment of a diamond. The stone is examined by trained graders using magnification, controlled lighting and measuring equipment, and the results are recorded against a set of agreed standards.
A report is not a valuation or an insurance document. It does not tell you what a diamond is worth in pounds. What it does is describe the stone objectively, so you can compare one diamond with another on a like-for-like basis rather than relying on a seller's description alone.
The two names you'll see most: GIA and IGI
GIA (Gemological Institute of America)
Founded in 1931, the GIA is a non-profit institute and the organisation behind the 4Cs system — cut, colour, clarity and carat weight — and the D-to-Z colour scale used across the industry today. GIA reports are widely regarded as a benchmark for natural diamonds, and many in the trade consider their grading to be consistent and conservative.
IGI (International Gemological Institute)
IGI was founded in Antwerp in 1975 and operates laboratories around the world. It grades both natural and laboratory-grown diamonds and has become the most familiar name on lab-grown diamond reports. IGI reports follow the same 4Cs framework, so the grades will look familiar if you have seen a GIA report before.
So which is better?
Both are respected, independent laboratories. Rather than treating one as "good" and the other as "bad", the more useful habit is to compare like with like: if you are weighing up two diamonds, it helps if both are graded by the same lab. Different laboratories can occasionally differ by a grade on colour or clarity, so a direct comparison across labs is never quite as precise as it looks on paper.
How to read a report, section by section
- Report number: a unique reference you can check on the laboratory's own website. Always do this — it confirms the report is genuine and matches the details you've been given.
- Shape and cutting style: for example "Round Brilliant" or "Oval Modified Brilliant".
- Measurements: the diamond's dimensions in millimetres. These matter more than many people realise, because two stones of the same carat weight can look quite different in size face-up.
- Carat weight: recorded to two decimal places.
- Colour grade: on the D-to-Z scale, where D is colourless. Most of our clients find the near-colourless range offers a lovely balance of beauty and value, particularly in yellow or rose gold settings where a hint of warmth is barely noticeable.
- Clarity grade: from Flawless (FL) down through VVS, VS and SI to Included (I). What matters most is whether inclusions are visible to the naked eye — many VS and some SI stones look perfectly clean when worn.
- Cut grade: given for round brilliants (Excellent, Very Good and so on). This is the grade that most affects sparkle, so it is worth prioritising.
- Polish, symmetry and fluorescence: finishing details and how the stone reacts to ultraviolet light. Fluorescence is often harmless and occasionally even helpful, but it is worth a conversation.
- Plotting diagram: a map of the diamond's main inclusions, which acts almost like a fingerprint for that stone.
- Inscription: many reports note a laser inscription on the girdle (the diamond's outer edge), usually the report number, so the stone can be matched to its paperwork.
Lab-grown diamonds and their reports
Laboratory-grown diamonds are real diamonds — the same material, physically and chemically — and they should always be clearly identified as lab-grown on their report and, usually, on the girdle inscription. If a report doesn't state the origin of the diamond clearly, ask why. Grading terminology for lab-grown stones can vary between laboratories, so read each report carefully rather than assuming it mirrors a natural diamond report exactly. If you're weighing up the two, our article on why now is a good time to buy a diamond covers how both markets have been moving.
Four tips from the trade
- Check the report number online with the issuing lab before you buy.
- Look beyond the headline grades. Measurements, proportions and the cut grade tell you far more about how a diamond will actually look on the hand.
- Don't pay for what you can't see. The jump from VS1 to VVS1, or from F to D, can add considerably to the cost without any visible difference once set.
- Remember the report is the starting point. Two diamonds with identical paperwork can still differ in life and character. An experienced eye is invaluable here.
Choosing a setting that shows the diamond off
Once you understand your diamond, the setting is where its personality comes through. For a well-cut round brilliant, a classic four-claw solitaire such as Harper keeps the focus entirely on the stone, while Kate offers a similarly clean silhouette on a slightly sturdier band. If you'd like a little extra sparkle on the hand, Aria pairs a round centre stone with a delicate pavé band. And for a sleek, modern look with excellent protection for the diamond's edge, the bezel-set Pearl is hard to beat.
Curious why the round brilliant performs so well under a grader's lamp? Our piece on the history of brilliant cut diamonds explains how its proportions were developed to maximise sparkle.
Buy with confidence, not confusion
A grading report should give you peace of mind, not a headache. Whenever we propose a centre stone, we're happy to walk you through its report line by line — explaining what each grade means for how the diamond will look, and where you can sensibly save without compromising on beauty.
Ready to start? Design your bespoke engagement ring with Wave Jewellery, or open the chat on this page to ask us anything about diamonds, grading reports or settings. We'll help you find a stone you can be sure of.