A grading report is only as useful as the laboratory behind it. Knowing what labs do, and what they leave out, keeps a report in proportion.
Diamond and gemstone reports come from independent laboratories that examine stones and record what they find. The best known is the Gemological Institute of America (GIA), and there are several others. A report adds confidence to a purchase, but it is not a price tag, a guarantee of beauty or a description of the ring as a whole. Here is what labs do and how to use their reports well.
What a laboratory does
| Service | What it tells you |
|---|---|
| Identification | What the stone is: diamond, sapphire, imitation, natural or laboratory-grown |
| Treatment detection | Whether the stone has been treated, where the lab can detect it |
| Grading | For diamonds: carat weight, color, clarity and, for round brilliants, cut |
| Measurements and proportions | Exact size and shape data |
| Inscription | An optional laser inscription of the report number on the girdle |
Labs do not appraise. A report describes the stone without assigning a money value; an appraisal is a separate service, covered in insuring an engagement ring.
The main laboratories
GIA is a nonprofit institute founded in 1931. It developed the D-to-Z color scale and the clarity scale that most of the industry uses, and its reports are the most widely recognized for natural diamonds.
IGI, the International Gemological Institute, was founded in Antwerp in 1975 and has laboratories in many countries. It grades a large share of laboratory-grown diamonds sold today, as well as natural diamonds and jewelry.
Other labs operate regionally or specialize, for example in colored gemstones, where reports focus on identification, treatments and sometimes geographic origin. Our sapphire guide explains what colored stone reports cover.
Why the lab matters
Grading uses standardized lighting, instruments and comparison stones, but color and clarity grades still involve trained human judgment. Labs differ in how strictly they apply the scales, and the trade has long noted that grades from some labs are not directly comparable with others. The practical rule is simple: compare stones graded by the same lab. A G color from one lab and a G color from another are not guaranteed to look the same.
Laboratory-grown diamonds
Laboratory-grown diamonds have the same chemical composition as natural diamonds, and reports state clearly that they are laboratory-grown. Report formats for laboratory-grown stones differ between labs and have changed over time, so read what a particular report includes rather than assuming it matches a natural diamond report line for line.
What a report doesn’t tell you
- Price. Two stones with identical grades can differ in price because of cut details, fluorescence or market factors. See diamond fluorescence for one example.
- How it looks in motion. Bow-ties, brightness and sparkle are best judged in videos; see diamond shapes compared.
- The setting. Metal, side stones and workmanship are outside the report.
- Durability in use. A report notes inclusions, but it does not rate how a stone will hold up in a particular ring.
- Anything after grading. If a stone is chipped, recut or treated after grading, the report no longer describes it.
Good to know: Before buying, look up the report number on the lab’s website, compare the measurements with the stone, and use a loupe to read the laser inscription if there is one. These three checks take minutes and tie the report to the diamond.
Reading the report itself
Once you trust the lab, read every section, including the comments line and the clarity plot. Our guide to reading a diamond grading report goes through it line by line, and gemstone treatments explains the treatment notes that can appear on reports.
Quick notes
- Independent laboratories identify stones, detect treatments and grade diamonds, but they do not set prices.
- The Gemological Institute of America developed the color and clarity scales most labs use today; IGI is another large lab, widely used for laboratory-grown diamonds.
- Grading involves human judgment, so comparing stones graded by the same lab is the fairest comparison.
- Verify any report on the lab’s website and check that its measurements and any inscription match the stone.
Common questions
Q: Is a GIA report better than an IGI report?
A: Both are widely used. GIA is the most widely recognized lab for natural diamonds, and many buyers prefer its reports for that reason. IGI grades a large share of laboratory-grown diamonds. Compare stones within the same lab rather than across labs.
Q: Do colored gemstones get grading reports?
A: Colored stones usually get identification reports rather than grades. These confirm the species, whether the stone is natural or laboratory-grown, detected treatments and sometimes an opinion on geographic origin.
Q: Can a diamond be regraded?
A: Yes. A diamond can be submitted to a lab again, and grades occasionally change, for example after a stone is repolished. A report describes the stone as it was when graded.
Q: Does a report prove a diamond is natural?
A: A report from a reputable lab states whether the stone is natural or laboratory-grown, based on testing. Matching the report to the stone, through measurements and any laser inscription, is what ties that conclusion to the diamond in front of you.