Lab Grown Diamonds
What the Report Does Not Tell You
Six things a grading report is silent about β several of which matter more than the grades printed on it.
Written by the Mapple Gems workshop, Surat Β· Updated 1 October 2026
Short answer
A report is an accurate description of a stoneβs measurable properties, and it deliberately says nothing about six things: cut quality on any fancy shape (only rounds are cut-graded), whether the stone is eye-clean, how it actually performs in light, the bow-tie, how the colour will read once it is set in metal, and anything at all about the ring. Those gaps are why rotating video and the ring specification sit alongside the report rather than after it.
Grading reports are honest documents that do exactly what they claim. The problem is that buyers treat them as a complete assessment, and they were never designed to be one.
A report describes a stone in isolation, and you will never once look at it in isolation β which is why its most important silence is about the setting. Colour is graded face-down against a white tray under controlled lighting, because that is the only way to make grading repeatable. You will wear the stone face-up, surrounded by metal, in whatever light you happen to be in. In that condition a warm setting reflects into the pavilion and masks tint, so an H reads as white as an F in yellow gold β and in white gold or platinum the same H can show what the grade was measuring. The report cannot tell you this, because it does not know what the ring will be. The same isolation applies to clarity: it is assessed at 10Γ, so βeye-cleanβ is not a grade and appears nowhere, which is why a well-positioned SI1 routinely beats a badly-positioned VS2 that costs more. The practical consequence is that you should choose the metal first and the colour grade second β and that buying above what the setting requires is money handed back for nothing visible.
The six silences
| Not on the report | Where to get it |
|---|---|
| Cut grade on fancy shapes | Rotating video, ordinary light |
| Whether it is eye-clean | Video, plus the plot diagram |
| Light performance | Video β and proportions as a proxy |
| The bow-tie | Handheld video, never a lightbox |
| How colour reads when set | Decide the metal first |
| Anything about the ring | The written specification |
Only rounds get a cut grade
The largest gap, and the least known. No laboratory grades cut on any fancy shape β not oval, pear, marquise, emerald, cushion, radiant or princess. Proportions are printed, but no judgement is made about them.
So two ovals with identical carat, colour and clarity can perform completely differently, and nothing on either report will say so. On a round the cut grade does that work for you; on everything else the responsibility transfers to the buyer, silently.
Two things fill the gap. Rotating video in ordinary indoor light, and measurements against standard β a stone measuring larger than standard for its weight has been cut shallow, which the report records as a measurement rather than as a criticism.
Two grades that hide behind one word
Worth knowing because listings exploit it without lying. Polish and symmetry are two separate grades, and a listing quoting βExcellent finishβ is usually quoting the better of the two. Read both lines.
Similarly, the comments line at the bottom carries real information in small type. βClouds are not shownβ is common and worth asking about on an SI stone, since an unmapped cloud can affect transparency in a way the clarity grade does not fully convey.
One line that matters more than the grades
The inscription number on the girdle. It is the only thing tying a piece of paper to a specific stone β without it, a report is a document about some diamond somewhere.
Two habits: check the inscription under magnification against the report number, and verify the report on the laboratoryβs own website using that number rather than trusting a supplied PDF. Both take a minute, and together they are the entire authenticity question.
And a note on comparing reports across labs
Since 1 October 2025, GIA reports lab grown diamonds as Premium or Standard rather than with full 4Cs, while IGI and GCAL continue to issue full grades. So a GIA report and an IGI report on lab grown stones are no longer comparable cell by cell, and a stone with one is not straightforwardly better or worse than a stone with the other.
Where two reports are from the same laboratory, they compare properly. Where they are not, fall back on the things that are objective in both: measurements, proportions and the plot β plus the video.
What to ask for alongside it
- Rotating video in ordinary indoor light β not a lightbox, which flatters every stone equally.
- The written ring specification: metal and karat, gram weight, shank width and thickness, accent count and size.
- The metal decision first, so the colour grade can be chosen to suit it rather than the other way round.
- A photograph from underneath, showing the gallery β the most revealing image of any ring and one nobody publishes.
- Confirmation the inscription matches, checked on the stone rather than taken on trust.
None of that contradicts the report. It sits around it β which is exactly the position a report was designed to occupy.
Keep reading
Frequently asked questions
Does a grading report tell me if a diamond is eye-clean?
No β clarity is assessed at 10Γ magnification, and βeye-cleanβ is not a grade and appears nowhere on a report. That is why a well-positioned SI1 routinely looks better than a badly-positioned VS2 that costs more. Use the plot diagram and rotating video.
Why is there no cut grade on my oval diamond?
Because no laboratory grades cut on any fancy shape β only round brilliants. Proportions are printed but no judgement is made, so two ovals with identical grades can perform completely differently. Rotating video and measurements-against-standard fill that gap.
Are GIA and IGI lab grown reports comparable?
Not cell by cell since 1 October 2025, when GIA moved to Premium and Standard descriptors for lab grown diamonds while IGI and GCAL continued issuing full 4Cs. Where reports come from different labs, compare the objective lines instead β measurements, proportions and the plot.
What is the most important line on a report?
The girdle inscription number β the only thing tying the paper to that specific stone. Check it under magnification against the report number, and verify the report on the laboratoryβs own website rather than trusting a supplied PDF.
Tell us the metal before you pick the colour grade.
It is the one decision the report cannot make for you, and the one that decides whether a higher grade is money well spent.
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