Reading a diamond report: GIA vs IGI vs AGI

D-VS1 for $899, and D-SI1 for $1,300. Liori Diamonds sells a pair of basket-set studs holding 1.00 carat total weight of lab-grown diamond, graded D-VS1 by AGI, at $899. It also sells a single loose 1.00 carat round brilliant lab-grown diamond, D-SI1, GIA-certified, at $1,300. The cheaper item carries the better clarity grade on paper.

Nothing there is dishonest, and nothing there is comparable. Two things differ underneath those two lines — the laboratory that issued the grade, and whether one carat means one stone or two — and this guide is about both. Everything below comes from the brands' own certification, product and policy pages as recorded in our brand files on 4–5 September 2026.

What a report is, and what it is not

A grading report records what one laboratory observed in one stone under its own standards: the 4 Cs, the measurements, and any treatment it detected. It is a description, not a valuation, not a guarantee of resale, and not a document that travels across issuers unchanged.

That last point does most of the damage. Grades are comparable within a laboratory's own system. Between systems they are two different opinions rendered in the same alphabet, which is why this site keeps naming the lab in the same breath as the grade.

Who graded what, across our fifteen

Two of the fifteen brands we cover put a third-party report in your hand. The rest publish grades, or publish nothing, on their own authority.

D-VS1 is not one thing

Liori's certification page names three laboratories, which means a D grade bought from one storefront can come out of three different systems. On the $899 studs it is AGI. We read AGI as materially less stringent than GIA, so a D-VS1 on an AGI report and a D-VS1 on a GIA report are not the same claim about the same stone.

The practical rule follows directly: never compare two stones on grade and price alone unless the same laboratory issued both reports. If the reports differ, the cheaper stone may simply have been graded by a more forgiving house — and no amount of arithmetic on the price will reveal it.

Where no laboratory is named at all, as at Fiametta and AMANDA PEARL, the grade is the seller's description. That is a defensible way to sell jewelry and a poor basis for a price comparison. Our lab-grown versus natural guide sets out which of our brands sits where.

Carat total weight is not carat

The second half of the opening comparison. "1.00 ctw" on the $899 studs is one carat spread across two stones — roughly half a carat each. "1.00 carat" on the $1,300 loose lab-grown stone is one carat in a single stone. A single stone of a given weight costs more than the same weight divided in two, and it is a visibly different object.

The abbreviation does the hiding. Liori's entry studs at $499 are 0.50ctw, which is a quarter-carat pair. At the other extreme, the $4,990 Kwiat Riviera necklace at Gwynn's states 1.01 CTS, GH colour, VS2-SI1 — one carat spread across a whole necklace of graduating stones, on a listing that never states whether the diamonds are natural or lab-grown. All three listings are accurate. None of them is describing the same thing.

Two other units to keep straight: karat measures gold purity and carat measures stone weight, and a point is a hundredth of a carat, so a twenty-five-point stone is 0.25 ct.

The arithmetic does not resolve any of this either. Worn weekly for five years the $899 studs are $3.46 a wear and the $1,300 loose stone $5.00 — except that a loose stone is not a wearable object at all, and our file holds no price for the setting it would need.

An appraisal is not a grading report

Noémie ships a gemologist-prepared appraisal report with each piece, intended for insurance. That is useful and it is a different document. An appraisal states a value for a stated purpose; a grading report states observed characteristics. An appraisal cannot tell you what a stone is, and a report will not tell you what to insure it for.

Two related documents are worth the same scepticism. Liori offers a lifetime full-value trade-in of up to 100% of the purchase price toward another item, explicitly void on sale and promotional items — a trade-in value is set by the seller, not by a laboratory or a market. And Noémie's "Google Top Quality Store" and "CCA Winner" graphics are brand-supplied images rather than verified credentials.

The clearest case is Liori's own FAQ, which describes the business as accredited by the Better Business Bureau with an A- rating. The Bureau's own record shows the business is not accredited, and rates it A+. A badge is not a document.

How to use this

Ask for the report number, then verify it yourself on the issuing laboratory's own site rather than reading a scan the seller supplied. Check that the report names the laboratory you were told, and that it is marked laboratory-grown where the stone is lab-grown.

Read the weight line carefully: is this figure carat, or carat total weight, and across how many stones? Then read the treatment line, and if there is not one, ask why. Softer and treated stones change the care instructions as well as the price, which is where our ring-sizing guide picks the subject up.

Finally, do all of this inside the window. Fiametta gives seven days to request a return and Liori's own pages state fourteen while a product badge says thirty; the full board of return terms has every one of them. A report that arrives after the window has closed is a description of something you already own.

Certification language, grades, prices, warranty and trade-in terms are drawn from each brand's own pages as recorded in our brand files on 4–5 September 2026, and the Better Business Bureau record from the Bureau's own listing. Terms change without notice. The Pennyweight buys nothing, accepts no gifted product, and is not affiliated with any brand or laboratory named here.