How to Read an IGI Report, Line by Line
An IGI report is not a score out of ten. It is a set of measurements taken on one stone, and the numbers that decide how that stone looks in a ring are the proportions — not the clarity letter everyone reads first.
The header: which stone this report is about
Every IGI report opens with an identifying block: report number, issue date, shape and cutting style, and a plain statement of what the stone is. On lab-grown stones that reads "Laboratory-Grown Diamond" rather than "Diamond".
Check it against your invoice first. Number, weight, shape and the words "laboratory-grown" should match what you were sold; a report describing a round brilliant is not a report for the oval in the box. IGI also runs an online lookup, and the paper carries a hologram and a QR code.
Measurements: the first line that matters
"Measurements: 6.52 – 6.56 × 3.98 mm" is minimum diameter, maximum diameter, depth. The gap between minimum and maximum tells you roundness: 0.04 mm is a true circle, 0.15 mm is a visibly oval outline that sits crooked in a four-prong setting.
The first number gives spread — a 6.5 mm round brilliant is roughly one carat — and it is the number a jeweller needs, because settings are cut to millimetre seats and nobody sizes a seat from "1.00 ct".
Table and depth: the two percentages
Table percentage is the width of the flat top against the average diameter; total depth percentage is height against the same average. On a round brilliant, a table of 54–58 per cent and a total depth of 60–62.5 per cent is where well-cut stones land.
Read them as a pair. A shallow stone leaks light out of the bottom and shows a grey fish-eye through the table. A deep stone keeps light inside the pavilion and hands it back as darkness — and hides weight: a one-carat stone at 64 per cent depth measures like a 0.90 ct. You pay for weight that never faces up.
Crown and pavilion: where light is handled
Crown angle is the slope above the girdle, pavilion angle the slope below. A 34–35 degree crown over a 40.6–41 degree pavilion is the classic pairing, with crown height around 14–16 per cent. What matters more is that they suit each other: a steeper crown over a slightly shallow pavilion still returns light, while two shallow angles give a glassy stone even when every grade reads well.
Girdle and culet
The girdle is what the prongs grip. "Medium to slightly thick" is the answer you want: an extremely thin girdle chips at the prong tips, an extremely thick one is a band of weight you paid for that never shows from above.
The culet is the facet at the bottom. "None" or "pointed" is normal; "medium" or larger is a visible dark dot at the centre of the table, an old-cut trait that in modern goods usually means a cutter working to weight rather than light.
Fluorescence
None, faint, medium, strong, very strong, usually with a colour noted — blue most often. For most stones it changes nothing you can see. In a minority, strong fluorescence makes a diamond look faintly hazy in daylight, and no report tells you which kind you have. That is a judgement made with the stone in hand.
Why the cut numbers beat the clarity letter
Clarity describes what is inside, at ten-power magnification. Most VS and SI inclusions are invisible at arm's length on a finger, and a well-placed SI1 can look cleaner than a badly placed VS2. Cut is visible from across a room: it decides whether the stone throws light or sits there.
So read the report in this order — proportions, colour against the metal it will be set in, clarity, fluorescence. A very good cut at 61 per cent depth out-performs a flawless stone at 66 per cent every time it is worn.
Reading the Comments on a lab-grown report
Comments is free text, and on a lab-grown diamond it carries two things. The first is the disclosure line — "This is a man-made diamond" — which says in plain words that the stone was grown, not mined. Its absence would be unusual and worth questioning.
The second is the growth method: CVD or HPHT. Neither is superior; both produce diamond. But HPHT-grown stones can carry a faint blue cast, and CVD-grown stones can show internal strain and occasionally a brownish tone that is sometimes improved after growth, in which case the report should note the treatment.
| Line on the report | Range worth having | What it changes |
| Measurements | Min/max within 0.05 mm | Size and setting fit |
| Table % | 54–58 | How much flat top you see |
| Total depth % | 60–62.5 | Spread for the weight paid |
| Crown angle | 34–35° | Contrast and fire |
| Pavilion angle | 40.6–41° | Light return to the eye |
| Girdle | Medium to slightly thick | Chip resistance at the prongs |
| Culet | None or pointed | No dark dot through the table |
| Comments | Man-made line plus method | Disclosure; what to inspect |
What we make
We cut and set stones in our own factory in Wuzhou, Guangxi, where we have been working since 2008. Lab-grown diamonds ship with IGI reports — the document above, growth method stated in the comments — while moissanite carries a GRA card, a different document with different limits.
Pieces run $17 to $2,020, most around $98, in 925 silver and 9K, 14K or 18K gold. Shipping is free over $99 and $5.99 below it, and unworn pieces in original packaging can come back within 30 days — long enough to put a stone under a loupe and see whether the paper matches.
