IGI-Certified Lab-Grown Diamonds: What IGI Certification Means and How to Verify a Report

The short answer: "IGI certified" means the International Gemological Institute, an independent gemological laboratory, examined that specific stone and issued a grading report. For a laboratory-grown diamond, the report identifies the stone as laboratory-grown and records its shape, measurements, carat weight, color, clarity and (for round brilliants) cut grade. You can check the report number on IGI's website. A report describes the stone. It is not a price appraisal or a promise about future value.

Most of the stones we list are graded by IGI, and a smaller number carry GIA reports. Every listing links to the stone's report on the lab's own website, so this guide covers what you'll see when you click that link and how to use it.

What "certified" actually means

Jewelers and shoppers say "certificate", but the document is a grading report. A gemologist examines the diamond under controlled conditions and records its measurable characteristics. IGI's own description of its report says it covers "the gemstone's description (natural or laboratory-grown) as well as its shape, cutting style, measurements and 4Cs assessment: Carat Weight, Color, Clarity and Cut."

Three things follow from that:

  1. The report is tied to one stone. It carries a unique report number, and IGI laser-inscribes that number on the stone's girdle (more on this below).
  2. It is an independent opinion, not the seller's. It's why a report is more useful than a retailer's own description, ours included.
  3. It doesn't set a price. Two stones with identical grades can look different and sell for different prices. The report gives you a common language for comparing them.

What an IGI laboratory-grown diamond report records

Layouts change over time, but an IGI Laboratory Grown Diamond Report typically includes:

  • Report number and date.
  • Description, which states that the diamond is laboratory-grown. IGI says it screens every diamond to determine whether it is natural, laboratory-grown or a simulant.
  • Shape and cutting style, for example "Round Brilliant" or "Oval Brilliant".
  • Measurements in millimeters (length × width × depth). Use these to compare size, because carat is a weight, not a dimension.
  • Carat weight. One carat is 200 milligrams.
  • Color grade. For colorless to near-colorless stones this is the familiar D-to-Z style letter grade. Fancy-color stones get a hue and intensity description instead, such as "Fancy Vivid Blue".
  • Clarity grade, on the scale popularized by GIA: FL, IF, VVS1, VVS2, VS1, VS2, SI1, SI2, I1–I3.
  • Cut grade for round brilliants. IGI's scale runs from Ideal (its top grade) through Excellent, Very Good, Good and Fair. Fancy shapes usually receive no overall cut grade.
  • Polish and symmetry, which describe the finish.
  • Fluorescence.
  • A proportions diagram and often a clarity plot.
  • A comments section. Don't skip it (see below).

The comments section: growth method and post-growth treatment

For laboratory-grown diamonds, IGI's comments can tell you a lot. In an announcement on its website, IGI explained that its lab-grown reports outline the growth process (CVD or HPHT). For untreated stones, the report says they are "as grown with no indication of post-growth treatment". For other CVD-grown diamonds, it notes that the stone "may include post-growth treatment."

Post-growth treatment is common in the laboratory-grown category. According to GIA, many colorless CVD crystals come out of the growth chamber with a brownish tint that is removed by heat treatment. Treatment isn't a defect, but you should know about it, and the report is where it's disclosed. We cover this in more detail in our guide to CVD vs HPHT lab-grown diamonds.

The "LG" laser inscription

IGI states that every laboratory-grown diamond it reports on has the prefix "LG" laser-inscribed on the girdle ahead of the report number, and that the inscription is noted in the comments. IGI also prints its laboratory-grown reports with a yellow cover. The inscription is microscopic: you won't see it with the naked eye, but a jeweler with a 10× loupe or microscope can read it and match it to the report.

How to verify an IGI report yourself

You don't have to take anyone's word for a report, including ours.

  1. Find the report number. On our listings it appears in the specifications table next to "Grading lab", and the "Verify IGI report" link opens IGI's own report-check page for that number.
  2. Check it on IGI's site. Go to IGI's "Verify Your Report" page and enter the number. If no record comes back, don't buy the stone until you know why.
  3. Match the details. Compare the carat weight, measurements, color, clarity and (for rounds) cut grade on IGI's record with the listing. They should agree exactly.
  4. Read the comments. Look for the growth method, the as-grown or treatment wording, and the inscription.
  5. Match the inscription once you have the stone. A jeweler can confirm that the number on the girdle matches the report.

IGI and GIA: what changed in 2025

You may see GIA reports on some laboratory-grown diamonds, including a smaller share of ours. GIA changed its service for colorless to near-colorless laboratory-grown diamonds on October 1, 2025. It now issues a "Laboratory-Grown Diamond Quality Assessment" that describes stones as Premium or Standard instead of giving individual color and clarity letter grades. GIA said it would "no longer use the nomenclature created for natural diamonds to describe what is a manufactured product." Trade press reported that IGI, by contrast, continues to give individual 4Cs grades on laboratory-grown stones.

What this means for you:

  • Older GIA laboratory-grown reports with full color and clarity grades remain valid, according to GIA's statements reported by JCK. The GIA-graded stones in our catalog show individual grades like those.
  • Newer GIA assessments won't have letter grades, so comparing them one-for-one with IGI-graded stones is harder.
  • Neither lab is a shortcut to "the best stone". Use the report to confirm what the stone is, then judge its appearance with the video and measurements.

What a report doesn't tell you

A grading report is necessary, but it isn't the whole picture:

  • How the stone looks as a whole. Two VS1 stones can differ in where the inclusions sit. That's why most of our listings include a 360° video of the stone itself.
  • Price or value. A grading report is not an appraisal, and no report predicts resale value.
  • How it will look in a setting. Metal color and setting style can change how a stone's color reads, so the letter grade is only part of the picture.

Using IGI reports when you shop with us

You can shop by shape, such as round and oval diamonds, or browse all white diamonds and fancy-color diamonds. For each stone:

  • open the report link and confirm the record matches the listing;
  • compare measurements, not just carat weight;
  • read the growth method and treatment comments;
  • watch the 360° video where one is available.

For a quick primer on carat, color, clarity and cut, see the 4Cs section of our FAQ. If anything on a listing doesn't match the lab's record, contact us before you buy.

Related reading: CVD vs HPHT Lab-Grown Diamonds: How They're Made and Whether It Matters · Laboratory-Grown vs. Natural Diamonds: What's the Same and What's Different

FAQ

Is IGI a legitimate grading lab? Yes. IGI is an independent gemological laboratory that grades both natural and laboratory-grown diamonds and publishes a report-verification tool on its website. It is one of the most widely used labs for laboratory-grown diamonds.

Does an IGI report prove a diamond is lab-grown? The report states the stone's origin. IGI says it screens every diamond to determine whether it is natural, laboratory-grown or a simulant, and laboratory-grown stones carry an "LG" prefix in the girdle inscription.

What does "LG" before the report number mean? It stands for laboratory-grown. IGI inscribes it on the girdle ahead of the report number for every laboratory-grown diamond it reports on.

Can I verify a report without the paper document? Yes. Enter the report number on IGI's "Verify Your Report" page. The online record is what you should compare against the listing.

Is an IGI report better or worse than a GIA report? They are different documents. Since October 1, 2025, GIA describes new laboratory-grown stones as Premium or Standard. IGI continues to give individual color, clarity and cut grades. Either way, confirm the report matches the stone and judge the stone by how it looks.

Does certification affect resale value? We don't make resale or investment claims about any diamond. A report helps you know exactly what you're buying. It isn't a statement of value.

Sources

Reviewed September 2026 against the sources above. Lab policies change, so check the lab's own site for the latest.

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