GIA and IGI are two of the most widely used gemmological laboratories in the world. Both grade natural and laboratory-grown diamonds, and both issue reports that are recognised internationally. This article describes them neutrally; it does not rank them.
The laboratories
| GIA | IGI | |
|---|---|---|
| Full name | Gemological Institute of America | International Gemological Institute |
| Founded | 1931, United States | 1975, Antwerp |
| Status | Non-profit institute | Independent laboratory |
| Known for | Developing the 4Cs and its international grading system | A large international network, widely used for laboratory-grown diamonds and finished jewelry |
| Verification | Online report check | Online report check |
What their reports have in common
- Colour, clarity and carat weight on the same D-to-Z and Flawless-to-Included scales.
- Measurements, polish, symmetry and fluorescence.
- A clear statement when a diamond is laboratory-grown.
- Optional girdle inscription of the report number.
Where differences arise
Grading involves expert judgement, and different laboratories may apply standards differently. Some in the trade regard GIA as the reference for natural diamonds; IGI grades a very large share of laboratory-grown diamonds. Report formats and the detail they include also vary, particularly for laboratory-grown stones.
How to compare fairly
- Compare stones graded by the same laboratory whenever possible.
- Look beyond the grades: measurements, proportions and, above all, the stone itself.
- Verify every report number online before you buy.
This article is general information. Laboratory services and report formats change; check each laboratory's own website for current details.
Reading either report
Whichever laboratory issued it, a report follows a similar logic. Start with identity: is the stone natural or laboratory-grown, and has any treatment been detected? Then the 4Cs, then the finish grades, polish and symmetry, then fluorescence and measurements. Finally, look at the comments section, where laboratories note details that do not fit elsewhere.
Other laboratories
GIA and IGI are not the only independent laboratories. Others, such as HRD Antwerp, are also widely recognised, and national laboratories exist in several countries. The same advice applies to all of them: know which laboratory graded the stone, verify the report and compare like with like.
Questions to ask a seller
- Which laboratory graded this stone, and can I verify the report?
- Is the report number inscribed on the girdle?
- If I am comparing two stones, were they graded by the same laboratory?
- Is there anything in the comments section I should know about?
Sources: Gemological Institute of America (gia.edu), about GIA; International Gemological Institute (igi.org), laboratory information.
Frequently asked questions
Is GIA stricter than IGI?
Opinions in the trade differ, and grading can vary between any two laboratories. The safest approach is to compare stones graded by the same laboratory.
Can I trust an IGI report?
IGI is a large, established independent laboratory. As with any report, verify the number online and check that it matches the stone.
Should I only buy diamonds with a GIA report?
Not necessarily. What matters is that the report comes from a recognised independent laboratory, that it can be verified and that you compare stones on a like-for-like basis.
Do both laboratories grade lab-grown diamonds?
Yes. Both issue reports for laboratory-grown diamonds that state their origin.
