An IGI certificate is the independent grading report the International Gemological Institute issues for one diamond: it records the carat weight, colour, clarity, cut and exact measurements under a unique report number you can look up on igi.org. At Carat Club Co., the Essential Diamond Solitaire Studs start at HK$2,300, and every Essential stone is individually IGI-certified.
Most people open an IGI report, glance at the carat weight, and close it again. That is the one number the report hardly needs to tell you, because you can already see it. The lines that decide whether a diamond actually looks good sit further down the page, and they are the ones nobody explains.
So here is the report, read properly, in the order that matters.
First, what an IGI report is and what it is not
The International Gemological Institute is an independent lab. It did not make your diamond and it does not sell your diamond. It measures the stone, grades it against a published scale, and issues a report with a unique number. That independence is the entire point. A grade from the person selling you the stone is a marketing claim. A grade from a lab that has no stake in the sale is a measurement.
What a report is not: a valuation. IGI will not tell you what the diamond is worth, and any seller who waves a certificate around as proof of value is using it for something it was never designed to do. The report tells you what you are holding. What it is worth is a separate conversation, and it is one about pricing, not paperwork.
A lab-grown diamond report also states plainly, on its face, that the stone is laboratory grown. There is no hiding it and no reason to. A lab-grown diamond is a real diamond, the same crystal as a mined one. The difference is where it formed, not what it is.
What does an IGI certificate look like?
IGI grades lab-grown diamonds on the same scales it uses for natural ones: colour from D to Z, and clarity from IF (Internally Flawless) down to I3. A VS1 on a lab-grown report means what a VS1 means on a natural one, so you can compare grades without a conversion table.
The report sets out the shape and cutting style, the measurements, the four Cs and the report number, which on an inscribed stone matches the laser inscription on the girdle. IGI also issues a separate Lab Grown Diamond Jewelry Report for diamonds already set in a piece, and its cover is yellow, so it is easy to tell apart from a loose-stone report at a glance.
Source: IGI, Lab Grown Diamond Report, page updated 18 August 2026.
The four lines that actually matter
1. Cut, and it is not close
Cut is the only grade on the report that describes human skill rather than raw material. It governs how light enters the stone, bounces around inside it, and comes back out at your eye. Everything you think of as a diamond looking alive is cut.
An Excellent cut on a modest stone will usually out-sparkle a Good cut on a bigger, cleaner one in the light you actually live in: office strip lights, an overcast Hong Kong afternoon, a dim restaurant. A poorly proportioned diamond leaks light through its base and goes flat and glassy in exactly those moments.
If you are trading one grade against another to stay in budget, protect cut. Give ground elsewhere.
2. Colour, but only relative to your metal
Colour runs D (colourless) down through the alphabet as a faint warmth creeps in. IGI groups D, E and F as colourless, and to an unaided eye in normal light they look the same. You are not going to spot the difference between D and F across a dinner table, and neither is anyone else.
What does change the read is the metal you set it in. A colourless stone against platinum or white gold looks icy and clean, and any warmth in the stone shows up against that cold background. Set the same stone in 18K yellow or rose gold and the metal casts a little warmth into it anyway, which means a G or an H can look completely at home while costing meaningfully less. Matching stone to setting is a lever most buyers never pull.
3. Clarity, judged at arm's length and not through a loupe
Clarity describes internal features. On an IGI lab-grown report the scale runs from IF down through VVS, VS and SI to I. Here is the part sellers rarely volunteer: the grading happens under magnification, and you do not wear your diamond under a loupe.
A VS stone is very often eye-clean, meaning that at normal viewing distance you see nothing. Paying up from VS to VVS buys you a better line on a piece of paper and, frequently, no visible change at all. On earrings in particular, where the stone sits a metre or so from anyone looking at it, chasing top clarity is one of the easiest places to overspend.
4. The measurements, which nobody reads
Near the bottom of the report there is a line of millimetres. This is the single most useful number on the page for earrings and almost nobody looks at it.
Carat is a weight, not a size. Two stones of identical carat weight can present very differently on the ear depending on how that weight is distributed. A stone cut deep carries its mass downward, hidden inside the setting, and shows a smaller face. A well-proportioned stone puts the weight where you can see it. The millimetre measurement tells you what you will actually look at. Carat tells you what you paid for.
Checking the report belongs to the diamond
A certificate is only worth something if it is the certificate for your stone. Three checks, all of them quick.
Take the report number and enter it into IGI's own verification tool on their website. The record should load and it should match the document in your hand on every field. If it does not load, or the details differ, stop.
Many certified stones carry a laser inscription on the girdle, the thin band around the widest part of the diamond. It is invisible to the naked eye and needs magnification, but a jeweller can show it to you in seconds. The inscription should be the report number.
And for a pair of earrings, read both reports. Two stones can each be individually excellent and still make a badly matched pair if their measurements or colour grades are a step apart. Symmetry across the pair is what your eye reads first, before it reads either stone on its own.
How Carat Club Co. handles certification, honestly
We do not claim that every diamond we sell arrives with its own IGI report, because that would not be true. Each product page states exactly what its own stones carry, and that page is the one to trust.
On the three stud earrings below, the pages say it plainly. The stones in the Essential Diamond Solitaire Studs and the Statement Diamond Solitaire Studs are individually IGI-certified and laser-inscribed with a serial you can verify online. Each 1.0ct pear in the Paradigm Pear Diamond Studs is individually IGI-certified.
The Seamless Diamond Tennis Bracelet works differently. Its listed price, from HK$13,500, covers the piece itself and does not include IGI certificates. IGI certification is available on request at HK$350 per stone, so you can certify one sample stone, the whole line, or none.
Say what is true and let people decide. That is the whole policy.
Pieces where the certificate does the talking
Can you check an IGI certificate yourself?
Yes. Enter the report number on igi.org and the online record should match your document field by field. On a laser-inscribed stone, a jeweller's loupe will show the same number on the girdle. Our step-by-step guide covers both checks: how to verify an IGI certificate yourself.
The short version
Protect the cut. Match the colour to your metal instead of buying the top of the scale. Stop at eye-clean on clarity. Read the millimetres, because that is the diamond you will actually see. Then verify the report number against IGI directly, and check both stones if it is a pair.
A certificate is not a trophy. It is a receipt for the truth, and it only counts if you read it.
