What a grading report actually tells you
A grading report is one page of numbers and abbreviations, and most of it is doing less work than you think. Two lines on it decide how the stone actually looks. Here is the whole page, in order, in plain words.
Who wrote it, and why that matters
A report is an opinion from a laboratory, not a fact from the stone. Different labs grade to different standards, and the same diamond can come back a grade apart depending on who looked at it.
The names you will see most are IGI and GIA. Both are real laboratories with real standards. What you should be wary of is a report from a lab nobody has heard of, or worse, a shop's own in-house certificate, which is a shop grading its own stock.
Our certified stones carry IGI reports, and where a stone is certified the report comes with the piece.
Carat is a weight, not a size
One carat is exactly 0.2 grams. That is all the number means.
It does not tell you how big the stone looks from above, which is what you actually see on a hand. A shallow-cut one carat can look wider than a deep-cut one carat, because the deep one is carrying its weight downwards inside the setting where nobody sees it.
If face-up size matters to you, look at the millimetre measurements further down the report rather than the carat weight.
Colour is a letter describing absence
The scale runs D, E, F at the top, then G through J, then onwards. D means no detectable colour. The further down the alphabet, the warmer the stone.
The thing nobody tells you is that this grade is assigned with the stone upside down against a white card, under controlled light, by someone comparing it to master stones. That is not how you will ever see it. Set face up in a ring, on a hand, the differences between neighbouring grades mostly disappear.
Yellow and rose gold warm a stone visually, so a lower colour grade in a yellow setting is a sensible trade. In platinum or white gold, a very warm stone has nothing to hide behind.
Clarity tells you how much, not where
Flawless at the top, then internally flawless, then VVS1 and VVS2, VS1 and VS2, SI1 and SI2, then the I grades.
From VS2 upwards you are generally not seeing anything without magnification. SI1 and SI2 are where it becomes a real question, and that question is not how many inclusions but where they are.
The report answers this, and almost nobody looks. There is a plotting diagram, a little map of the stone with the inclusions marked on it. An inclusion drawn near the centre sits under the table and you will see it. One drawn at the edge sits near the girdle and the setting will cover it.
If the report has a plot, read the plot. It tells you more than the grade letter does.
Cut is the only graded decision
Excellent, Very Good, Good, Fair, Poor. On round brilliants most labs grade this fully. On fancy shapes many do not, and the line is simply not on the page. You get polish and symmetry instead.
This is the line that decides whether a stone looks alive. It is also the one most likely to be quietly skipped in a listing that leads with carat and colour.
If a listing tells you the carat, the colour and the clarity but not the cut, assume the cut is the weakest of the four and ask.
The measurements line, which nobody reads
Something like 6.42 to 6.45 by 3.99 mm. Two widths and a depth.
The two widths tell you how round a round actually is. If they differ by much, the stone is out of round. The depth against the width gives you the depth percentage, which is roughly how much of the weight is hidden below the girdle.
For a round brilliant, a depth percentage in the low sixties and a table in the mid fifties as a percentage of width is the comfortable zone. Fancy shapes run their own numbers, so do not hold an oval or a pear to a round brilliant's figures. Outside the zone for its own shape, look at photographs before you decide anything.
Polish and symmetry
Two separate grades on the same scale as cut. Polish is how smooth the facet surfaces are. Symmetry is how well the facets line up with each other.
Both matter less than cut, and the difference between Excellent and Very Good in either is not something you will see. Do not pay a premium for them.
Fluorescence
None, faint, medium, strong, very strong. It describes a faint blue glow under ultraviolet light.
Treat it as neutral. In warmer stones it often helps them read whiter in daylight, and stones with it frequently cost less. At the strong end in a very white stone, ask to see a photograph.
What the report does not cover
This is the important part.
- How the stone looks. No grade captures brightness, and two stones with identical reports can look different. Only a photograph of the actual stone settles it.
- A bowtie. Ovals, pears and marquises can carry a dark band across the middle. It appears on no report and shows in every real photograph.
- Whether it suits you. Reports do not know your hand, your setting or your metal.
- Value. A report grades, it does not price.
What to actually do with it
- Check which lab wrote it.
- Read the cut grade first, not the carat.
- Look at the plotting diagram and see where the inclusions sit.
- Glance at the measurements for depth and roundness.
- Then ask for a photograph of the stone itself, because the report cannot show you that.
The short version
- A report is a lab's opinion, so the lab's name matters.
- Carat is weight, not visible size. The millimetres tell you that.
- Colour is graded upside down under lab light, which is not how you will see it.
- Clarity's grade letter matters less than the plot showing where the inclusions are.
- Cut is the only graded decision and the one you see from across a room.
- Nothing on the page tells you how the stone looks. Ask for the photograph.
Send us a report you are looking at and we will read it back to you in plain language, whether the stone is ours or not.
