Certification (20%), GIA, IGI, AGS, and When Each Is Enough

Twenty percent of every Caratlytics score comes from a single question: who graded this stone?

Not what they said about it. That's handled by the Cut and Specifications components. The Certification score asks which laboratory's name sits on the report, and whether that lab's grading standards are trustworthy enough to take at face value. If you haven't read the full breakdown of how the Caratlytics methodology works, start there for the broader picture. This piece focuses narrowly on one component: why certification carries the weight it does, how we tier the major labs, and what the penalties look like when a stone is graded by a lab we don't fully trust.

Not all labs are created equal

Diamond grading has no single regulatory body. Laboratories certify themselves, set their own standards, and answer to no central authority. Some grade conservatively. Some grade generously. A few grade so loosely that their reports function more as marketing collateral than independent scientific assessment.

We track stones from over 110 retailers across our index of 8.8 million scored diamonds. The grading labs attached to those stones fall into four tiers in our methodology, each with a ceiling on how many of the 20 available certification points a stone can earn.

Tier	Labs included	Certification score ceiling
1 (Full marks)	GIA	Full 20 points available
2 (Minor deduction)	AGS, GCAL	Up to 18 points available
3 (Contextual)	IGI	Up to 16 points on naturals, up to 18 on lab-grown
4 (Heavy penalty)	Uncertified or unrecognised labs	Maximum 8 points

Those ceilings reflect two things: the price premiums the market actually assigns to each lab's reports, and the consistency of grading we observe when the same physical stone carries reports from multiple laboratories. Both inputs matter. A lab can be popular without being accurate, and we want the score to capture accuracy.

One important clarification. A Tier 1 stone with mediocre cut proportions still won't score well overall. The certification component doesn't rescue a bad diamond. It ensures that a well-cut stone graded by a trusted lab gets full credit for both qualities, rather than being dragged down by a report the market would discount.

Why GIA still leads on naturals

GIA's dominance in natural diamond grading isn't prestige. It's measurement consistency, and we can see it in the data.

Across our index, we observe thousands of cases where the same diamond has been submitted to multiple labs. Colour and clarity grades on GIA reports cluster more tightly around what experienced gemologists would independently assess. IGI and other labs tend to grade one step more generously on colour and sometimes two on clarity. This isn't a secret; it's well known in the trade. But the implication is concrete: a "G colour, VS2" from GIA and a "G colour, VS2" from IGI frequently describe different levels of quality in the actual stone.

The market prices this accordingly. GIA graded naturals command a persistent premium over otherwise identical stones carrying reports from other labs. Resellers and wholesalers trust GIA grades more, which feeds directly into what retailers pay for inventory, which determines what you pay at checkout. Buying a GIA graded natural diamond means buying tighter tolerances on every grade printed on the report, and the premium you pay for that accuracy tends to hold at resale.

Our scoring treats GIA as the reference standard for naturals because the market does. We don't penalise other labs for existing. We recognise that the secondary market, the insurance industry, and wholesale trading desks all treat GIA reports as the benchmark. Our scores reflect that reality rather than argue with it.

IGI and the lab-grown question

IGI's position on lab-grown diamonds is materially different from its position on naturals. Our scoring reflects that distinction.

Most major lab-grown producers now submit to IGI as their primary grading lab. The reasons are partly practical (IGI has more global locations and faster turnaround) and partly economic (GIA charges higher fees, and lab-grown margins are already compressed). The outcome: IGI has become the de facto standard for lab-grown certification. When the vast majority of lab-grown stones carry IGI reports, the cross-retailer consistency question shifts. You're comparing IGI to IGI, not IGI to GIA, and within that frame the comparisons hold.

Our scoring gives IGI only a minor deduction on lab-grown stones: up to 18 of 20 points, the same ceiling AGS and GCAL receive on naturals. The market made this call collectively, and the pricing data supports it. Lab-grown buyers comparing stones graded by the same laboratory are making valid, like for like comparisons. Penalising them for the industry's choice of grading body would be punitive rather than informative.

Average Caratlytics scores reinforce the point. Lab-grown diamonds average 74.2 across our index, compared to 71.7 for naturals. Part of that gap traces directly to certification patterns: lab-grown stones are more consistently certified (usually by IGI), while the natural market still carries a long tail of uncertified and poorly documented inventory pulling the average down.

For a thorough comparison of how GIA and IGI reports differ in practice, covering colour accuracy, clarity consistency, and real price spreads, our GIA vs IGI diamond certification comparison goes much deeper than we can here.

Why uncertified is a false economy

Uncertified diamonds look cheaper. They are cheaper. That's precisely the problem.

A retailer selling an uncertified stone is asking you to trust their own grading. Some retailers grade honestly. Many grade optimistically, because generous grading means higher prices on stones that would otherwise trade for less. Without an independent lab report, there's no way to verify colour, clarity, or even carat weight beyond what the seller claims.

The apparent savings, often 15 to 30% below a comparable GIA graded piece, frequently evaporate once you account for the likelihood of generous grading. The maths is straightforward. If a retailer has graded a stone one step high on colour and one step high on clarity, the "discount" you're seeing is just the correct market price for the stone's actual quality. You're not saving money. You're buying a lesser stone at its fair value, without the documentation to prove what it actually is.

Consider a 1.5ct G VS2 round brilliant. An uncertified version with those stated specs typically sits 20 to 25% below its GIA graded equivalent across our index. Tempting at first glance. But if that stated G is really an H or I, and the VS2 is closer to SI1, the buyer has paid market rate for a lower quality stone with zero documentation. Resale becomes nearly impossible without a recognised report. Insurance valuations become guesswork. The "saving" was never real.

Our scoring flags this risk directly. Uncertified stones cap at 8 of 20 points on the certification component. A hard ceiling, not a sliding scale. We'd rather overstate the risk and let buyers decide with full information than treat a missing report as a minor footnote.

The overall Caratlytics score distribution tells part of this story.

Grade band	Stones	% of index
A+ (90 to 100)	30,296	0.3%
A (80 to 89)	3,282,883	37.3%
B (70 to 79)	2,296,494	26.1%
C (60 to 69)	2,006,523	22.8%
D (below 60)	1,192,421	13.5%

Those 1.19 million stones sitting in the D band? A significant portion land there because of certification penalties alone. A stone can have decent cut proportions and reasonable colour, but still fall below 60 if it carries no recognised report. By design. The certification component isn't a gentle nudge. It's a filter.

Fancy colours play by different rules

Everything above applies to the D to Z colourless and nearly colourless range. Fancy colour grading is a fundamentally different problem.

GIA's fancy colour system is the only one with broad market acceptance. The gap between Fancy Light Yellow and Fancy Yellow, or between Fancy Intense Pink and Fancy Vivid Pink, can represent tens of thousands of dollars on a single stone. Other labs grade fancy colours too, but the wholesale market doesn't trade off those reports with the same confidence. A fancy colour report from a non-GIA lab tells you roughly what colour family the stone falls into. It doesn't tell you, with the precision the market demands, exactly where.

We score accordingly. Fancy colour diamonds without a GIA report receive the same treatment as uncertified stones: a maximum of 8 points on the certification component. Overpaying for a misgraded fancy colour is one of the most expensive mistakes a diamond buyer can make, and our scoring exists to flag that risk before it costs real money.

Pink, blue, green, orange. If the stone's value hinges on its colour grade, a GIA report isn't optional.

What we're watching on certification

Lab-grown grading is evolving quickly. GIA has expanded its lab-grown reporting programme, and we're monitoring whether the market starts assigning a premium to GIA lab-grown reports over their IGI equivalents. So far, it hasn't. If GIA graded lab-grown stones begin trading meaningfully higher, the tier structure will move with the data.

GCAL deserves attention too. Their reports include actual photomicrographs and light performance imagery as standard, something no other major lab provides. GCAL's current market share is small enough that cross-retailer pricing data remains thin, but if that changes, there's a solid case for Tier 1 status alongside GIA in certain categories. We'll follow the numbers.

Only 0.3% of the 8.8 million stones in our index currently score A+ (90 to 100). Certification alone won't get you there; every component of the methodology has to pull its weight. But weak or absent certification will reliably keep you out. That's 20% of the total score, settled before cut, colour, or value even enter the equation. The data says it earns its share every quarter.