IGI vs AGS vs GCAL: Which Lab Actually Matters
Three labs dominate lab grown diamond grading and they are not interchangeable. IGI is the volume leader, AGS built its reputation on cut, GCAL built its on light performance. Here is what each report actually tells you, and where it stops helping.
Why there are three names instead of one
The diamond trade never had a single authority. One lab set the vocabulary — colour, clarity, cut, carat — and everyone else grades against that vocabulary. IGI, AGS and GCAL each grew into a different niche inside it. So the useful question when you buy a lab grown stone online is not "which lab is best." It is "which lab's report answers the question I actually have." A report is a description, not a guarantee.
What IGI is good at
IGI, the International Gemological Institute, is the lab most associated with lab grown diamonds and with coloured stones. Its volume in grown diamonds is enormous, and that has a practical benefit: a very large share of the stones on the market carry an IGI report, so an IGI number is the easiest thing for a second jeweller, an insurer or a buyer to look up and compare. IGI reports follow the standard four Cs and, for grown stones, state the growth method — HPHT or CVD — and normally note post-growth treatment.
The trade-off is depth. IGI reports are consistent and widely accepted, but the cut section is conventional rather than exhaustive, and optical performance is not the point of the document.
What AGS is known for
AGS, the American Gem Society Laboratories, built its reputation on cut. Its light performance work — the ASET scope, the proportions-based cut grade from 0 to 10 — made it the lab jewellers cite when the argument is about how a stone handles light rather than how it scores on a spreadsheet. For a round brilliant, an AGS cut grade of 0 is a meaningful statement about brightness, fire and scintillation taken together, not a marketing label.
What GCAL does differently
GCAL, the Gem Certification & Assurance Lab, leans into optical performance and imaging: light return maps, brilliance and fire photography, a report that shows behaviour rather than only grades. GCAL also runs a guarantee programme tied to its grading. For a buyer who wants to see how one specific stone returns light instead of trusting a category grade, a GCAL report is the most visual of the three documents.
The three labs side by side
| Lab | Strongest at | Common in | Watch for |
| IGI | Volume, grown diamonds, coloured stones, growth method disclosure | Lab grown of every size | Cut section is standard, not forensic |
| AGS | Cut grading, proportions, light performance | Natural and high-end goods | Fewer stones carry it |
| GCAL | Optical imaging, light maps, guarantee | Premium and grown | Descriptive rather than directly comparable |
What this means if you are buying a lab grown diamond
Three practical conclusions. First, match the lab to the decision in front of you. Choosing between five stones on price and size? IGI gives you the cleanest apples-to-apples read. Paying a premium specifically for cut? An AGS or GCAL report is doing more work for your money.
Second, no report covers the setting, the metal or the workmanship. Those are the parts you actually wear, and they are where most disappointment lives — a perfectly graded stone in prongs that snag.
Third, a report is only as good as its number. Verify it on the lab's own site rather than trusting a PDF a seller emailed you.
Where the reports stop helping
No lab tells you whether the stone is priced fairly, whether the setting survives daily wear, or whether the seller answers an email in year three. A grown diamond report also creates no resale value. It documents what the stone is, not what a stranger will pay for it next year. Treat the document as a specification sheet, not an investment certificate, and you will make better decisions with it.
Why moissanite is not in any of these systems
Moissanite is silicon carbide, not diamond, and none of these three labs grades it as a diamond. It is graded to its own standard: the GRA card, which records colour and clarity — D colour, VVS1 in our case — plus measurements, and identifies the material. That is not a downgrade, it is a different category. A lab that grades diamonds by diamond criteria has nothing meaningful to say about a stone with double refraction and different dispersion.
How to read a listing
Find the lab name. Find the report number. Verify the number. Then stop reading and look at the return policy, because no document can tell you whether you like the stone on your hand in your own kitchen light.
What we make
We run our own factory in Guangxi, China, and have been making jewellery since 2008: 925 sterling silver, 9K, 14K and 18K gold, set with GRA D colour VVS1 moissanite and IGI certified lab grown diamonds. Pieces run from $17 to $2,020, with a median around $98. That range exists because a silver stud and an 18K solitaire are different objects, not because one is a stripped-down version of the other.
Every lab grown stone we sell ships with its IGI report, and every moissanite with its GRA card, so the paperwork identifies the material before you look at the stone. Shipping is free over $99, otherwise $5.99, and returns run 30 days on unworn pieces in original packaging. If a report number does not check out, that is a conversation to have before you order, not after.
