In the first guide I compared natural diamonds, lab-grown diamonds and moissanite. The next question is always the same: how do I know what I am actually buying? The answer is a piece of paper, the grading report. Most people call it a certificate. Here is how to read one, which laboratories issue them today, and the five things I would check before paying for any stone.
What is a grading report?
A grading report is a document from an independent gemmological laboratory. Its gemmologists have examined one particular stone and written down what they found. The seller does not write it. That independence is the whole point.
A good report tells you:
- What the stone is: natural diamond, laboratory-grown diamond, or something else
- Its 4Cs: cut, colour, clarity and carat weight
- Its exact measurements, to a hundredth of a millimetre
- Any treatment: for lab-grown diamonds, whether it was changed after growth
- A report number, usually laser-inscribed on the thin edge of the stone, the girdle
That last line matters more than people think. The inscription is too small to see without a loupe, but it ties the paper to the stone. If the numbers match, you know the report belongs to the diamond in your hand.
Is a grading report the same as a valuation?
No. A grading report describes the stone. It does not put a price on it and it does not promise what you could sell it for. A valuation, for insurance for example, is a separate document, usually prepared by a jeweller or appraiser.
Which laboratories issue reports today?
The names you will meet most often:
GIA (Gemological Institute of America). Founded in 1931 in the United States, and the laboratory that created the 4Cs. For natural diamonds it is the world reference. Since October 2025 GIA no longer grades lab-grown diamonds on the 4Cs. It now classifies them only as "Premium" or "Standard".
IGI (International Gemological Institute). Founded in 1975 in Antwerp. It grades both natural and lab-grown diamonds on the full 4Cs, and it is today the most widely used laboratory for lab-grown stones. Its lab-grown reports also state the growth method, HPHT or CVD, and whether the stone is "as grown" or shows signs of treatment after growth.
HRD Antwerp. A Belgian laboratory grading diamonds since 1973. From 2026 it grades only natural diamonds and no longer issues reports for loose lab-grown stones.
Two names you may still see on older paper: AGS Laboratories closed in 2022, and its light-performance grading is now offered by GIA as the AGS Ideal Report. And for moissanite, most stones come with a GRA card. It lists the stone's specifications, but it is not the same as an independent report from a laboratory such as GIA or IGI.
What should you check before you buy?
These are the five checks I would make myself.
- Get it in writing. The invoice should say plainly whether the stone is natural, lab-grown or moissanite. A reputable seller will not hesitate.
- Ask for an independent report. A "certificate" printed by the seller is a description, not a grading report.
- Check the report number online. GIA and IGI both let you enter the number on their websites and see the original record.
- Match the number to the stone. Ask the jeweller to show you the girdle inscription under a loupe.
- Look at the setting, too. A good stone deserves a good mount: secure prongs or bezel, solid metal, and a clear purity hallmark such as 925, 585 or 750.
Quick answers
Does every diamond need a report?
Not every small stone. The tiny diamonds set around a centre stone are rarely graded one by one. For a centre stone, a report is worth asking for.
Is a GIA report better than an IGI report?
For natural diamonds, GIA is the reference most traders use. For lab-grown diamonds, an IGI report currently gives you more detail, because it still grades the full 4Cs.
What does "as grown" mean?
It means the laboratory found no sign that the lab-grown diamond was treated after growth, for example to improve its colour.
Murat Bakış, Founder & Designer, Mu Design Jewelry · Ruse, November 2026
Sources: GIA, Laboratory-Grown Diamond Quality Assessment (October 2025) and AGS Ideal Report information; IGI, laboratory-grown diamond reporting of growth method and post-growth treatment; HRD Antwerp, announcement on ending loose laboratory-grown diamond certification from 2026; American Gem Society, closure of AGS Laboratories (2022).
