How do I verify a diamond’s laser inscription?

The laser inscription sits on the girdle, and you won't read it without at least a 10x loupe. It's not on the table. It's not something you can squint at in a jewelry case and hope to catch.

Start with a clean stone. Diamonds collect skin oil, lotion, and dust on the girdle faster than anywhere else, and that film will hide the lettering completely. I use a small drop of dish soap and warm water, scrub with a soft toothbrush around the edge, and dry with a lint-free cloth. Then I take the stone to my microscope, because a hand loupe will show the inscription but a microscope will actually let you read the spacing and the font.

What the inscription should look like

A GIA-graded natural diamond will usually have "GIA" followed by the report number, like GIA 2476543210. IGI laser inscriptions for lab-grown stones use an "LG" prefix before the number, for example LG 623456789. The text sits on the girdle, not the crown. The letters are around 50 microns deep. That's roughly half the width of a human hair.

Custom inscriptions, like a date or a name, get the same treatment. Read them twice under magnification before the stone is set. I once had to send an emerald-cut back because the engraver's software turned a lowercase 'r' into a 't' and no one caught it until the client's mother did.

If you're comparing to a paper report, match the number exactly, including leading zeros. Do not accept "close enough." A client named Daniel brought in a 1.20 carat round last April with a report that said GIA 2384759201 and a stone engraved GIA 2384759200. One digit off. It changed everything. The report was for a different diamond, almost identical on paper, slightly different in price. He walked away.

How to actually see it

Hold the stone table-down against a dark, non-reflective background. Tilt the girdle toward a single light source, not a broad one. The inscription will flash when the light hits the groove at the right angle. If you're using a microscope, use darkfield or low transmitted light, and ask your jeweler for the darkfield stop because many microscopes have one built in and most people never know it's there.

Rotate the stone slowly. The full inscription may run along a few millimeters of girdle. Don't expect to see it in one glance.

After you find the number

Look it up in the grader's online database. GIA has Report Check at GIA.edu, where you enter the report number and the carat weight. IGI has a similar verification page. If the report exists, compare the listed measurements, carat weight, color, and clarity to the stone in front of you. A laser inscription is not proof by itself. It's a cross-reference.

At my bench, I check the inscription under a microscope before I set a stone, in front of the client when possible. If the stone is going into a full bezel, the bezel will cover the girdle permanently, so reading the inscription before setting is the only chance. I won't set a stone into a bezel unless the client has seen the inscription or signed off on not caring.

When the inscription isn't there

Some older stones, antique cuts, and many colored diamonds were never inscribed. That's not a problem on its own. A missing inscription becomes a problem when the report says "laser inscribed" and the stone shows no sign of it. Then I start asking harder questions.

One more thing. A laser inscription can be polished off. It takes a little girdle work and it does not always leave an obvious mark. If you're buying a secondhand diamond with a report, and the inscription is missing, don't accept the seller's explanation at face value. Have an independent appraiser with a microscope verify the stone against the report's full measurements. A few hundredths of a millimeter difference may be the tell.

If you want to be certain, verification is not the same as authentication. The inscription tells you what the grader's database says. The stone in front of you is what you're actually buying.