Lab-Grown Diamonds · Certification

Diamond Certification Explained: IGI, GIA & How to Read a Report (2026)

By Tushar Leclerc · 9 min read

Last Updated: October 8, 2026

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A diamond certificate is the difference between taking a seller's word for a stone and having an independent expert confirm it. It is the single most important piece of paper in a diamond purchase, and yet most buyers have never read one. This guide explains what a certificate is, who issues them, how to read every field, and how to verify a stone is really the one on the report.

Why certification matters

When a jeweller tells you a diamond is "G colour, VS1 clarity, excellent cut," those are not facts you can see, they are grades, and grades are opinions until an independent lab confirms them. A certificate is that independent confirmation: a neutral third party, with no stake in the sale, grading the stone under controlled conditions.

Without it, you are trusting the seller to grade their own product, which is like a shop marking its own homework. A certified diamond can be compared fairly against any other certified diamond, priced correctly, insured accurately, and resold with proof of what it is. An uncertified stone, however pretty, is a gamble on the seller's honesty. The rule is simple: no certificate, no sale.

IGI vs GIA

Two laboratories dominate diamond grading, and both are legitimate, independent and widely trusted. The difference is mostly one of focus.

You will hear debate that GIA grades a touch more strictly on the margins. For a buyer the practical point is simpler: a stone graded by either lab comes with an independent, verifiable report, and that is what protects you. IGI is the standard for lab-grown diamonds and is what the whole lab-grown market runs on, which is why it is what we use. What matters far more than which of the two labs graded a stone is that it was graded by one of them at all, rather than by an in-house or unknown "certificate."

Round SolitaireFrom $1,288 Oval HaloFrom $1,530 Emerald SolitaireFrom $1,369 Cushion SolitaireFrom $1,369 Hidden Halo PavéFrom $1,611

How to read a grading report

A diamond report looks dense, but it is just a handful of fields. Here is what each one means, so you can read any IGI or GIA report with confidence.

• Report number. The unique ID for this stone. It matches the number laser-inscribed on the diamond and lets you verify it online (more below).
• Shape and cutting style. Round brilliant, oval, emerald cut and so on.
• Measurements. The stone's dimensions in millimetres, which tell you its real face-up size, not just its carat weight.
• Carat weight. The weight to two decimal places.
• Colour grade. D (colourless) to Z (tinted).
• Clarity grade. Flawless (FL) down to Included (I3).
• Cut grade. Excellent to Poor, the single biggest driver of sparkle.
• Polish and symmetry. How well the stone was finished and aligned; aim for Very Good or Excellent on both.
• Fluorescence. Whether the stone glows under UV light; "None" to "Faint" is typical and nothing to worry about.
• Origin / growth type. On a lab-grown report, this states the stone is laboratory-grown and names the method (CVD or HPHT). Our how lab-grown diamonds are made guide explains those.
• Comments and treatments. Any post-growth treatment is disclosed here. For colour, this is where "natural" versus "treated" is stated.

For what each grade actually means and which to prioritise for value, our 4Cs guide and quality chart cover the scales in full; this page is about the report itself.

The laser inscription and verifying online

This is the part that makes a certificate more than a piece of paper, and the step most buyers skip. Nearly every certified diamond has its report number laser-inscribed on the girdle, the thin edge around the stone, in letters far too small to see without magnification.

That inscription ties the physical stone to its report. To confirm a diamond is genuinely the one described:

• Find the report number on the certificate.
• Enter it in the lab's free online verification tool, IGI and GIA both have one on their websites, and the full report appears.
• Check it matches the stone you were shown: the same carat, colour, clarity and measurements.
• For total certainty, a jeweller can read the girdle inscription under magnification and confirm it matches the number on the report.

This is how you catch the oldest trick in the trade: a real certificate shown alongside a different, lesser stone. If the inscription and the online record both match what is in front of you, the diamond is exactly what the paper says.

Certificate vs appraisal

These two documents are often confused, and the difference matters. A grading certificate describes what the diamond is, its objective qualities, from a neutral lab. An appraisal estimates what it is worth in money, usually for insurance, and is produced by a jeweller or valuer, not the grading lab.

You need the certificate to know what you are buying. You may also want an appraisal afterwards for insurance, but an appraisal is not a substitute for a grading report, it is an opinion on value, which can be inflated, whereas the certificate is an independent statement of fact about the stone.

Every Riona stone is IGI-certified

Every diamond we sell is an IGI-certified lab-grown diamond, and the report comes with it. That means you can read the 4Cs for yourself, check the growth method, and verify the report number against IGI's own database rather than taking our word for anything.

It is also why we can price honestly: an independent grade is an independent grade, so a G/VS1 stone from us is the same G/VS1 it would be anywhere, at a fraction of the mined price. Certification is what makes a lab-grown diamond a known quantity rather than a leap of faith, and it is standard on every piece we make.

Round SolitaireFrom $1,288 Oval Three-StoneFrom $1,450 Emerald SolitaireFrom $1,369 Oval HaloFrom $1,530 Cushion SolitaireFrom $1,369

Frequently asked questions