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Diamond Certification: GIA vs IGI, Honestly Compared

Diamond certification GIA vs IGI: what each lab grades, how the rules changed for lab-grown stones in 2025, and when the report actually matters.

GIA and IGI are both independent gemmological laboratories, and both issue reports describing a diamond's quality. The practical difference right now is that GIA still grades natural diamonds on the familiar D-to-Z colour and Flawless-to-I3 clarity scales, but from 1 October 2025 it stopped applying those scales to lab-grown diamonds, describing them instead as "Premium" or "Standard". IGI continues to issue full 4Cs grades for both natural and lab-grown stones, which is why nearly every lab-grown diamond you see advertised with a specific colour and clarity grade carries an IGI report.

That single change explains most of the confusion customers bring to us. Below is what each report actually tells you, where the two labs genuinely differ, and where paying more for a particular piece of paper buys you nothing.

What a grading report is, and what it is not

A grading report is a laboratory's documented opinion about one stone on one day. Carat weight and measurements are measured. Colour and clarity are judgments made by trained graders comparing the stone against master sets under controlled lighting, and reasonable experts sometimes land one grade apart. Cut grade for round brilliants is calculated from proportions against the lab's own research, so it is more reproducible, but the research behind it is proprietary to each lab.

It is worth being blunt about what a report is not:

  • It is not a legal certificate. There is no Canadian statute that governs diamond grading the way the Precious Metals Marking Act governs the gold and platinum marks stamped inside your ring. The Competition Bureau's guide to that Act exists to "ensure that the information provided to consumers on the quality of a precious metal is truthful". Nothing in it addresses diamond grading.
  • It is not an appraisal. It carries no dollar value.
  • It is not transferable between stones, which is why the laser inscription on the girdle matters more than the paper.
  • It is not a guarantee of beauty. Two stones with identical grades can look different in the hand.

The vocabulary itself is regulated in the United States, and North American trade language follows it. The FTC Jewelry Guides define a diamond at §23.12 as "a mineral consisting essentially of pure carbon crystallized in the isometric system", permit "cultured" for laboratory-created stones only alongside "a clear and conspicuous disclosure" such as "laboratory-grown", and at §23.27 make it "unfair or deceptive to use the word 'real,' 'genuine,' 'natural,' 'precious,' 'semi-precious,' or similar terms to describe any industry product that is manufactured or produced artificially". Section 23.13 also reserves "flawless" for stones with no imperfections visible under 10-power magnification.

The October 2025 split: GIA changed how it reports lab-grown

GIA's older Laboratory-Grown Diamond Report gave full 4Cs specifications and, as GIA's own LGDR page still describes, stated whether the stone was grown by high pressure, high temperature (HPHT) or chemical vapour deposition (CVD), along with any post-growth treatment. Plenty of stones in the market still carry that report, and it remains readable and useful.

For stones submitted from 1 October 2025, GIA replaced that service with a Laboratory-Grown Diamond Quality Assessment. As reported by National Jeweler on 28 August 2025, "Premium" requires D colour, VVS clarity or better, excellent polish and symmetry, and an excellent cut grade for round brilliants; "Standard" covers E to J colour, VS clarity, very good polish and symmetry, and a very good cut grade for rounds. Stones meeting neither get no designation. GIA CEO Pritesh Patel said the company "will no longer use the nomenclature created for natural diamonds to describe what is a manufactured product", as quoted by Rapaport on 27 August 2025. The fee is US$15 per carat with a US$15 minimum, and US$5 for stones that do not qualify, which is roughly C$21 and C$7 per the Bank of Canada's daily USD/CAD rate of 1.3785 on 20 August 2026.

The consequence for you as a buyer is simple. On lab-grown diamonds, you can no longer compare a GIA-assessed stone against an IGI-graded stone grade for grade. One says "Premium", the other says "F VS1". They are not the same statement.

What IGI is, in plain numbers

IGI publishes its own figures because it is a listed company. Its 2024 Annual Report states that IGI was "Established in 1975 in Antwerp", founded by Marcel Lorie, and that as of 31 December 2024 it operated 31 laboratories and 18 schools of gemology across 10 countries with 672 gemologists. It issued 10.5 million reports in 2024 and describes a "rigorous 14-step grading process". Citing market researcher Redseer, the report puts IGI's share of laboratory-grown diamond certifications at roughly 65% globally and its overall global certification share at about 33% for CY 2023. IGI was acquired by Blackstone in May 2023 and listed on the NSE and BSE.

One detail from that report deserves attention, because it is usually stated loosely elsewhere. IGI says its laboratories "in BKC (Mumbai) and Surat are accredited under ISO/IEC 17025:2017 for testing and calibration", with a footnote clarifying that two of its major labs hold that accreditation. That is a real credential, but it applies to specific laboratories, not to all 31. If ISO accreditation matters to you, ask which lab graded your stone.

Natural diamonds: GIA is still the safer paper

For a natural diamond, we tell customers to buy GIA unless there is a good reason not to. This is not because IGI's gemmologists are careless. It is because the natural diamond market prices off GIA's scale, price steps between adjacent grades are large, and a stone that sells as G VS1 on one lab's report and H VS2 on another's is a real difference in money at resale or reappraisal.

The trade's working assumption, and ours, is that IGI's colour and clarity opinions on some material run a touch softer than GIA's. We should be honest that we cannot point you to a published, peer-reviewed head-to-head study proving this. It is trade experience, gathered stone by stone, and it does not apply uniformly across every lab location or every grade band. Treat it as a reason to discount rather than a reason to dismiss.

Where it genuinely does not matter: melee and side stones. Nobody certifies 1.3 mm pavé, and no lab report will tell you anything useful about them. Judge those by looking at the setting.

Which report to insist on

Your stoneWhat we would insist onWhyNot worth paying extra for
Natural, under 0.30 ctAny reputable lab, or nonePrice steps between grades are small in absolute dollarsA premium lab report costing a fifth of the stone
Natural, 0.30 to 0.99 ctGIAGrade-to-grade price gaps start to biteDuplicate reports from a second lab
Natural, 1 ct and aboveGIA, with inscriptionLargest dollar swing per grade; easiest to insure and resellExtra "light performance" add-on reports
Lab-grown, any sizeIGI, if you want 4Cs numbersGIA no longer states colour and clarity grades for lab-grownRe-submitting an IGI stone to GIA
Melee and side stonesNothingNot individually gradeable at that sizeAny certification claim on pavé

How to read either report without being fooled

  1. Check the inscription first. Ask us or any jeweller to show you the report number on the girdle under magnification. Paper without a matching inscription tells you nothing about the stone in front of you.
  2. Verify the number on the issuing lab's own report-check service, not on a retailer's website.
  3. Read the shape and measurements before the grades. A 1.00 ct round measuring 6.0 mm is cut deep and will look smaller than its weight.
  4. On a round, look at the cut grade, then polish and symmetry. On fancy shapes, remember that neither lab issues a full cut grade the way it does for rounds, so your eyes and the proportions do the work.
  5. Check the fluorescence line, and do not panic about it. Faint or medium blue fluorescence is usually invisible in wear and often costs less.
  6. On lab-grown reports, look for the growth method and any post-growth treatment note. HPHT-treated colour is a legitimate product, but it should be disclosed to you.
  7. Ignore the plotted inclusion diagram as a beauty guide. It shows position, not visibility. Ask to see the stone at arm's length instead.

What to do next

If you are buying natural, filter our loose diamond search to GIA-reported stones and set your cut grade before you set your carat weight. If you are buying lab-grown, filter to IGI and accept that "Premium" or "Standard" on a newer GIA assessment is a different kind of statement, not a worse one. Either way, pick your engagement ring setting alongside the stone rather than after it, since the setting decides how much of the diamond you actually see, then work through metal, size and engraving when you finish the ring. Our 3D preview will show you the pairing before you commit.

The report is a tool for pricing and identification. It is not a substitute for looking at the stone. If a report and your eyes disagree, trust your eyes, and ask us why the paper says otherwise. More detail on the individual grades is in our other guides.

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