LG is shorthand for laboratory-grown. On a diamond it appears as part of the tiny inscription laser-etched into the girdle, alongside the grading report number. It is an origin marker, not a grade and not a flaw: it is invisible without magnification and it does not change how the stone looks.
Last updated: August 2026
What does the LG inscription on a diamond mean?
It marks the stone as laboratory-grown. The letters sit on the girdle, the thin band around the widest part of the diamond, and in almost every case they share that line with a grading report number. The number identifies which record describes the stone; the origin shorthand tells you which kind of report it is.
One thing to be clear about, because a lot of pages are not: there is no single mandated format. Different laboratories and different cutters write the origin marker differently, and some stones carry a report number with no origin wording at all. Reading the letters is a hint. Looking the number up is the answer.
Where is the inscription and why can you not see it?
The girdle is the narrowest surface on a cut diamond and the only one that is not doing optical work, which is why it is where inscriptions go. IGI describes its LaserScribe process as using a very fine laser beam to place alphanumeric characters, and it can also place a brand logo or a personalised message there.
The characters are cut at a scale meant to disappear. A standard 10x loupe — the same magnification used for clarity grading — will sometimes show them if you know which side of the girdle to rotate into the light, but a gemmological microscope makes it far easier, and an unmounted stone is easier again because a setting can hide the inscribed section entirely. If a jeweller cannot find it in thirty seconds, that is normal, not suspicious.
Do lab-grown diamonds have to be marked LG by law?
Not by any inscription rule. In the United States, the jewellery guides at 16 CFR Part 23 govern how a stone is described in words. They require that a term such as “laboratory-grown” or “[manufacturer name]-created” immediately precede the stone name with equal conspicuousness, so a buyer cannot mistake it for a mined stone; they bar “real”, “genuine” and “natural” as descriptions of anything produced artificially; and they allow “cultured” only when it carries one of those qualifiers alongside it.
What Part 23 does not contain is any provision about girdle inscriptions. So an origin inscription is an industry practice and a laboratory service, not a legal marking requirement, and the disclosure the rules actually care about is the one in the listing, on the tag and in the description you were given. If you want the origin question settled rather than inferred, see how origin is documented and the IGI vs GIA comparison for what each laboratory’s report records.
What is actually written on the girdle?
Several different things, put there by different parties for different reasons. Confusing them is the usual source of alarm.
| What you see |
What it is |
Who put it there |
What it proves |
| A long alphanumeric serial |
A grading report number |
The laboratory, as a service |
Which record describes the stone |
| LG, LAB GROWN, LABORATORY-GROWN |
An origin marker |
The laboratory or the cutter |
The stone was grown, not mined |
| A logo or brand name |
A maker or house mark |
The cutter or the brand |
Who cut or sold it, not how it grades |
| Initials, a date, a short phrase |
A personal inscription |
The retailer, at a buyer’s request |
Nothing gemological at all |
| Nothing |
No inscription applied |
Nobody |
Nothing, in either direction |
| A number that does not resolve |
A mismatch, an error or a fake |
Unknown |
That the stone needs independent testing |
Does an inscription change how a diamond looks or what it is worth?
No on the first, and not directly on the second. The girdle is the edge of the stone, so an inscription there is outside the path light takes through the crown and pavilion — nothing about brilliance, fire or the face-up appearance changes. It is not a clarity characteristic either; the graded fields describe what was in and on the stone before anyone etched it. The 4Cs explainer covers which of those fields you can actually see with your eyes.
Where an inscription earns its keep is administrative. It binds one stone to one report, which is what stops paperwork from being quietly moved to a different diamond, and it makes a stone identifiable after a repair, a resize or a theft. That is worth something, but it is worth it as record-keeping, not as a feature of the diamond.
What if your diamond has no inscription at all?
It means nothing on its own. Inscription is a service that is ordered and paid for, not a step every graded stone goes through, so plenty of properly graded diamonds carry no marks on the girdle. Older stones frequently have none. A setting can also cover the inscribed section, so “no inscription” often turns out to mean “not visible from this angle”.
The productive move is the same either way: take the report number and check it against the laboratory’s own records, then compare the fields it returns against the stone. If the numbers, weight and measurements agree, you have a real chain. If they do not, that is the finding.
What can an inscription not tell you?
It cannot tell you the stone is genuine, because an inscription is just characters cut into a surface and can be faked. IGI published a case in 2021 in which a 6.18 carat round brilliant came in for checking with a report describing a natural diamond of matching quality; IGI’s gemologists determined that the stone was grown rather than mined, and a fake laser number had been inscribed on it to make the deception complete. Only laboratory testing separates grown from mined stones — IGI screens every gemstone it receives specifically to establish whether it is naturally mined, laboratory grown or a simulant.
Nor does an inscription tell you the growth method, the presence of treatments, or the grades. Those live on the report; IGI notes the growth process and any treatments in the comments section on request. Beyond Carat’s answer to this is deliberately narrow: every diamond is graded by IGI, the International Gemological Institute, and the report ships in the box rather than following later. The honest concession is that it is IGI only, with no GIA option, so a buyer who needs a specific laboratory’s letterhead is better served elsewhere.
Frequently asked questions
Does LG on a diamond mean it is fake?
No. LG marks the stone as laboratory-grown, and a laboratory-grown diamond is a real diamond — same carbon structure, same hardness, same optical behaviour as a mined one. What LG separates is origin, not authenticity. Simulants such as cubic zirconia are a different material entirely.
Can you see a laser inscription with the naked eye?
No. The characters are cut on the girdle at a scale that needs magnification. A 10x loupe can show them if you rotate the right section into the light; a microscope is easier, and an unmounted stone is easier still because a setting can cover the inscribed area.
Can a laser inscription be removed or faked?
Both, which is why an inscription is a check rather than a proof. Girdle characters can be polished off and false ones can be added — IGI has documented a stone that arrived carrying a fake laser number. Only laboratory testing settles what a stone actually is.
