Lab Grown Diamonds
Which Laboratory Graded It, and Why That Now Matters
Reports from different labs stopped being comparable in October 2025 β and most listings have not caught up.
Written by the Mapple Gems workshop, Surat Β· Updated 9 October 2026
Short answer
Since 1 October 2025 GIA has reported lab grown diamonds as Premium or Standard rather than with full 4Cs, while IGI and GCAL continue to issue full colour and clarity grades. So two lab grown stones with reports from different laboratories cannot be compared cell by cell, and a stone with one is not straightforwardly better or worse than a stone with the other. Compare same-lab reports where you can; where you cannot, fall back on measurements, proportions, the plot and rotating video.
For years the practical advice was simply βbuy a certified stoneβ. That is still right, and it is no longer sufficient β because the certificates are now answering different questions.
A grading scale is not a measurement of a stone β it is a comparison against a set of reference stones and a house standard, and those differ between laboratories. This has always been true and it mattered little when everyone published the same four grades, because a buyer could compare like with like even if one lab ran slightly stricter than another. What changed in October 2025 is that the outputs themselves diverged. A GIA report on a lab grown diamond now describes colour and clarity together as Premium or Standard, on the reasoning that laboratory production clusters so tightly at the top of both scales that fine distinctions carry little meaning. IGI and GCAL took the opposite view and continue to grade in full. Neither approach is wrong, but the consequence for a buyer is concrete: a βPremiumβ and a βVS1 Fβ are not two ways of saying the same thing, and no conversion table exists between them. So a listing that shows one stone graded by one lab beside another graded elsewhere is presenting an apples-to-oranges comparison, usually without meaning to. The one number that survives every scale is the measurements line β millimetres, depth, table percentage β because those are measured rather than judged.
What each report gives you
| On a lab grown stone | GIA (since Oct 2025) | IGI / GCAL |
|---|---|---|
| Colour and clarity | Premium / Standard | Full grades |
| Carat weight | Yes | Yes |
| Measurements | Yes | Yes |
| Cut grade (rounds only) | Rounds only | Rounds only |
| Cut on fancy shapes | None | None |
| Girdle inscription | Yes | Yes |
Two rows are worth dwelling on. No laboratory grades cut on any fancy shape β that is universal and unchanged, so on an oval, pear, emerald or cushion the cut assessment is yours regardless of which lab issued the paper. And the inscription is the only line that ties a report to a specific stone.
How to compare across labs
- Compare same-lab reports wherever possible. Ask a seller whether they can show you two stones graded by the same laboratory β a workshop with stock usually can.
- Use the measurements line as the common ground. Millimetres, depth percentage and table percentage are measured, not judged, and they mean the same thing everywhere.
- Check measurements against the standard for the weight. A round sold as one carat should be about 6.5Β mm; larger means cut shallow to spread.
- Open the plot diagram. Position beats grade on any scale β an inclusion near the girdle is covered by a prong, one under the table is not.
- Insist on rotating video in ordinary indoor light. It settles what no scale reports: light performance, the bow-tie, and whether a stone is eye-clean.
Verify the report, not the printout
Independent of which laboratory, two checks take a minute and settle authenticity.
Look up the report number on the laboratoryβs own website rather than trusting a supplied PDF or photograph. And check the girdle inscription under magnification against that number β a report belongs to a stone, not to a ring, and the inscription is the only thing connecting them.
One related note: melee under about 0.20Β ct is never individually certified in any material, by any laboratory. So accent stones always come as a parcel description, and the thing to ask for is the parcel specification β material, colour and clarity range, millimetre size and count.
Does the lab change what a stone is worth?
Honestly: it can change what a stone is priced at, because buyers pay for familiar paperwork. It does not change the stone.
What we would rather people spent the attention on is the part no laboratory covers at all β the ring. Gram weight, shank thickness at the base, whether every point and corner has a prong over it, whether the gallery is open. A report describes a stone in isolation, and you will never once look at it in isolation.
And the same caution as always applies to moissanite: no laboratory grades it at all, so any colour or clarity claim on a moissanite is a seller assessment regardless of how the document is laid out.
Keep reading
Frequently asked questions
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 grades. No conversion table exists between them, so compare same-lab reports where you can.
What can I compare across different laboratories?
The measurements line β millimetres, depth percentage and table percentage β because those are measured rather than judged and mean the same everywhere. Then the plot diagram for inclusion position, and rotating video for everything no scale reports.
Does the grading laboratory affect a diamondβs value?
It can affect the price, because buyers pay for familiar paperwork β but it does not change the stone. The attention is better spent on what no laboratory covers: gram weight, shank thickness, prong placement and whether the gallery is open.
How do I verify a report is genuine?
Look the number up on the laboratoryβs own website rather than trusting a supplied PDF, and check the girdle inscription under magnification against it. A report belongs to a stone rather than to a ring, and the inscription is the only thing connecting them.
Ask which laboratory graded it β then compare the measurements.
It is the one line that means the same thing on every report, from every lab, in every market.
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