What is the AGS cut grade actually measuring?

The AGS Performance Grading Standard ray-traces the actual stone and measures four light-performance outputs: brightness (total light return), contrast (the dark / light pattern the eye reads as scintillation), dispersion (fire — the rainbow flashes), and leakage (light that escapes through the pavilion instead of returning to the eye). Those four are graded on a continuous 0 to 10 scale and combined with proportion, polish, and symmetry to print the final cut number. AGS 0 means the measured light output matches the AGS reference pattern under ASET imaging.

What does each AGS cut grade number mean — 0, 1, 2, 3?

AGS 0 is Ideal: top-of-standard brightness, contrast, dispersion, and minimal leakage, with proportion, polish, and symmetry also at 0 (sometimes written AGS 000 to make the triple-zero explicit). AGS 1 is Excellent — one tier below Ideal, typically a measurable leakage band or a minor contrast asymmetry; the visual gap to AGS 0 is invisible to non-trade observers but carries a 3–5% trade price gap on $5,000–$15,000 naturals. AGS 2 is Very Good, roughly the middle of the GIA Excellent band on proportions with one or two metrics measurably softer. AGS 3 to 4 is Good to Fair, with visible leakage or weak contrast the ASET image will surface. AGS 5+ is Poor — functionally the same warning a GIA Poor verdict carries. The lower the number, the better.

What does an ASET image actually show?

ASET (Angular Spectrum Evaluation Tool) is a hemisphere that surrounds the diamond and replaces ordinary light with three coded zones — red for light arriving at high angles (40°–75°, the brightness band), green for light arriving at low angles (0°–40°, the contrast band), and blue for light coming from directly overhead (which the diamond should obscure as contrast). An ASET image of the stone shows where each band returns to the eye. Strong even red with controlled green contrast and minimal white (leakage) is what AGS 0 light-performance grading looks for.

Did AGS Laboratories really close in 2022?

Yes. AGS Laboratories ceased issuing standalone reports in late 2022. The Las Vegas facility, the ASET methodology, the AGS Performance Grading Standard intellectual property, the ray-tracing software, and the research staff transferred to GIA under an acquisition agreement. The science was not retired — it now ships as the AGS Ideal Report digital supplement available on qualifying GIA Diamond Grading Reports for roughly $25 per stone. The American Gem Society itself, the non-profit trade association, continues to operate separately from the closed lab.

When does the AGS 0 supplement actually change what I pay?

Three cases. First: round naturals above roughly $4,000–$5,000 where the cut premium is a material slice of the spend and AGS 0 isolates the top 10–15% of GIA Triple Excellents. Second: any round marketed as "super ideal" or "true hearts and arrows" — the supplement is what verifies the marketing copy. Third: lab-grown rounds in 2026, because GIA dropped granular 4Cs from its lab-grown report in October 2025 and the AGS Ideal supplement is the most defensible independent light-performance credential left on the document. Skip the supplement on rounds under that price band; GIA Excellent is enough.

How do GIA and AGS handle fluorescence differently?

Both labs grade fluorescence on a None / Faint / Medium / Strong / Very Strong scale and both report the colour of the fluorescence response under longwave UV (almost always blue). The reporting is essentially identical; the lab-to-lab difference here is small. The substantive fluorescence question — whether Medium or Strong blue fluorescence hurts a stone's appearance in daylight — is independent of the lab and is covered in the fluorescence guide linked at the bottom of this page.

Does AGS issue origin opinions for colored gemstones?

No. AGS Laboratories was a diamond lab. Colored-gemstone origin (Kashmir sapphire, Burma ruby, Colombian emerald, Paraiba tourmaline) is the domain of SSEF, Gübelin, AGL, and GRS, with GIA issuing country-of-origin opinions in many cases. If a stone is sold as colored-gemstone with an "AGS" paper, the document is either misidentified or fabricated.

AGS vs GIA: Cut Grade, Methodology, and When Each Matters in 2026

The AGS vs GIA decision is really two decisions stacked on top of each other: which grading philosophy you trust to judge a round brilliant's cut, and which report you can actually still get in 2026. The two labs were never measuring the same things the same way — GIA grades proportions and prints a categorical bucket, AGS measured light performance directly and printed a continuous numeric. AGS Laboratories closed in late 2022 and GIA acquired the science, so the question now is when the AGS Ideal Report supplement (roughly $25 added to a GIA report) is worth paying for and when it isn't. This page is the deep-dive: history, methodology, the acquisition, comparative reporting line-by-line, and a buyer's framework keyed to actual dollars.

Last updated 2026-06-22 · Edited by CaratWire Editorial Desk

A short history of AGS Laboratories

The American Gem Society was founded in 1934 by Robert M. Shipley, the same gemologist who founded the Gemological Institute of America (GIA) three years earlier in 1931. From the start the two organisations divided labour: GIA was the educational and research institute that defined the diamond grading scales the trade still uses; AGS was the retail trade association that enforced ethical-conduct standards on jeweller members. For sixty years AGS did not operate a grading laboratory of its own — its members relied on GIA reports.

That changed in 1996 when AGS opened AGS Laboratories in Henderson, Nevada — later moved to its long-running Las Vegas facility — explicitly as the lab arm of the trade association. The brief was narrow and unusual: build a cut-grading system that measured how a diamond actually handled light, not just whether its proportions fell inside a measurement bucket. The first AGS Performance Grading Standard for round brilliants went live in the mid-2000s, followed by the first peer-reviewed light-performance methodology paper in 2005. AGS extended the standard to qualifying fancy shapes — princess, emerald, oval, and others — through the late 2000s and 2010s, becoming the only major lab issuing a measured cut grade on fancy cuts at scale.

The chronology matters because the two labs reached cut grading from opposite directions and at different times. AGS had a measured, ray-traced cut grade in market by the mid-2000s. GIA did not introduce an official cut grade at all until January 2006, and when it did the rubric was deliberately conservative: a five-tier categorical scale (Excellent / Very Good / Good / Fair / Poor) anchored to proportion ranges and validated against observer panels, not ray traces. For roughly a decade — 1996 to 2006 — AGS was effectively the only lab issuing a cut verdict on a round brilliant at all. That head start is why "super ideal" brands built their entire marketing identity on AGS 0 paper, why the 2022 closure landed as a shock to that segment of the trade, and why the AGS Ideal Report supplement inside GIA in 2026 is not redundant with the GIA cut grade — the two grades are answering different questions about the same stone.

By 2020 AGS Platinum Light Performance reports were the trade reference for the top tier of round brilliants, especially "super ideal" brands like Hearts on Fire, Whiteflash A CUT ABOVE, and Brian Gavin. The closure in late 2022 was a corporate decision driven by economics — running a diamond lab at AGS's scale could not compete with GIA's volume — not a technical one. The science survived the corporate event, which is the load-bearing fact for any 2026 buyer.

The ASET methodology, end to end

The technical core of the AGS Performance Grading Standard is ASET — the Angular Spectrum Evaluation Tool. ASET replaces ordinary observation lighting with a colour-coded hemisphere that surrounds the diamond and divides incoming light by the angle at which it arrives at the stone. The diamond is photographed (and ray-traced) inside that hemisphere. The result is a four-colour map of where every angle of light is coming from, plus the absence of light where the stone has leaked it.

The four colours and what they mean:

Red — light arriving at high angles, roughly 45° to 75° from horizontal. This is the "brightness band", the angle ordinary room and jewellery-counter lighting comes from. Strong, evenly-distributed red across the table and crown is what a well-cut round returns most of.
Green — light arriving at low angles, 0° to 45°. This is the "contrast band", normally obscured by the observer's own head and shoulders. Green zones in the ASET image are where a real-world viewer's silhouette would be reflected back through the stone — what the eye reads as the dark facets that make scintillation possible.
Blue — light coming from directly overhead. In a real viewing situation this is the observer's own head. The diamond should obscure this band as additional contrast.
White — leakage. Light that the diamond accepted but failed to return to the observer, escaping through the pavilion. White zones in an ASET image are literally where the stone is losing light.

ASET imaging is paired with full ray-trace simulation against a 3D scan of the actual stone (not its proportion summary). The ray-tracer follows millions of light paths through the diamond, computes brightness, contrast, dispersion (fire), and leakage as numeric outputs, and grades each on the 0–10 scale. The combined verdict, plus proportion, polish, and symmetry, becomes the AGS cut grade.

The distinction from GIA matters because the two systems can disagree about the same stone. GIA grades the proportions: if a round's table, crown angle, pavilion angle, and so on fall inside the Excellent measurement bucket, the cut is Excellent — and the face-up appearance check is a relatively coarse pass. AGS grades the output: two stones can both be GIA Excellent yet measure differently under ASET, because the Excellent proportion bucket is wide enough to contain meaningfully different light-performance results. AGS 0 is the verdict that the stone's light output, not just its measurements, lands at the top of the standard.

This is also why AGS published a cut grade on fancy shapes while GIA still does not. A proportion-bucket system needs an idealised reference shape to score against; a light-performance system needs only a stone you can ray-trace. AGS issued measured cut grades on princess, emerald, oval, cushion, radiant, and (after 2018) Asscher and a handful of other shapes. GIA reports list polish, symmetry, and proportion measurements on fancy shapes but do not print an overall cut grade, because the rubric GIA uses is round-brilliant-specific.

What each AGS cut grade number actually means

The AGS cut grade is a continuous 0-to-10 scale where lower is better, marked in 0.5 increments, but in practice the top six tiers carry virtually all the price signal a 2026 buyer needs to act on. Reading from the top:

AGS 0 — Ideal. Brightness, contrast, dispersion, and leakage all measure at the top of the standard, and the three subcomponents — proportion, polish, and symmetry — score 0 as well. Sometimes written AGS 000 when sellers want the full triple-ideal credential explicit on the line. Practical effect: this is the top 10–15% of GIA Triple Excellent rounds, the segment that "super ideal" brands market against and the only AGS grade that earns a measurable trade premium on resale.
AGS 1 — Excellent. Light performance is one tier below Ideal — typically a measurable leakage band somewhere on the pavilion or a minor contrast asymmetry the ASET image will surface. Still a top-tier stone visually; the gap from AGS 0 to AGS 1 is usually invisible to a non-trade observer under ordinary lighting. Price gap to AGS 0 is typically 3–5% on naturals in the $5,000–$15,000 band.
AGS 2 — Very Good. Roughly parity with the middle of the GIA Excellent band on proportions, with one or two light-performance metrics measurably softer. A reasonable buy for value-conscious shoppers using AGS paper as a sanity check rather than as a top-tier credential — but not the stone to pay a "super ideal" premium against.
AGS 3 to 4 — Good to Fair. Light performance is measurably compromised; the ASET image typically shows leakage zones, weak contrast bands, or both — visible to a careful observer in person. The grade does its job here: it warns the buyer the stone is not what the marketing suggests, even when GIA proportions still print Excellent.
AGS 5+ — Poor. The stone has light-performance issues severe enough that AGS does not differentiate further along the 5-to-10 range on consumer-facing reports. Functionally the same warning the GIA Poor verdict carries.

The continuous numeric scale is what made the AGS cut grade uniquely useful in the trade and is why the supplement survived the 2022 closure: two stones that both score GIA Excellent can sit at AGS 0 and AGS 2, meaning the proportion bucket GIA uses is wide enough to span a visible light-performance gap. AGS 0 versus AGS 1 is the call that matters at "super ideal" price points. AGS 2 versus AGS 0 is the call that matters when a stone is marketed at a premium and the supplement doesn't back it up. Neither distinction is visible on a GIA-only report, which is exactly the gap the AGS Ideal supplement was rebuilt to close.

The 2022 acquisition: corporate timeline

The misconception that AGS science "died" in 2022 is the single most expensive misreading in the secondary market — buyers undervalue old AGS Platinum paper and sellers fail to add the supplement to new GIA reports. The actual timeline:

July 2022 — closure announced. AGS Laboratories announced the wind-down of standalone grading operations effective end-of-year.
Late 2022 — operations cease. AGSL stopped issuing standalone AGS Platinum Light Performance reports. The Las Vegas grading facility, the ASET methodology, the AGS Performance Grading Standard IP, the ray-tracing software, the research and grading staff, and the Performance Grading Standard reference database transferred to GIA under an acquisition agreement.
2023 — AGS Ideal Report launches inside GIA. GIA introduced the AGS Ideal Report, a digital supplement that can be added to an eligible GIA Diamond Grading Report or GIA Laboratory-Grown Diamond Report on qualifying round brilliants and a subset of qualifying fancy shapes. The price is roughly $25 per stone. The grading criteria are identical to the old AGS Platinum reports — same software, same standard, often the same research staff that ran AGSL.
2024–2026 — the trade adjusts. Pre-2022 AGS Platinum reports remain valid documents on the secondary market, especially among informed trade buyers. The American Gem Society itself, the non-profit trade association, continues to operate as a separate entity from the closed lab. An "AGS member jeweller" credential is a retailer-ethics signal, not a lab-grading signal.
October 2025 — GIA lab-grown report restructured. GIA dropped granular 4Cs from its lab-grown report and now prints a binary Premium / Standard tier. The AGS Ideal supplement became, by default, the most granular independent light-performance credential available on a 2026 lab-grown round.

The side-by-side rubric

Dimension	GIA	AGS (pre-2022)
Color scale	D → Z categorical	0.0 → 10.0 numeric, 0.5 steps
Clarity scale	FL, IF, VVS1–I3	0 → 10 numeric
Cut scale	Excellent → Poor categorical	0 (Ideal) → 10 (Poor) numeric
Cut methodology	Proportions + polish + symmetry + face-up appearance check	Ray-traced light performance + ASET imaging
Cut on fancy shapes	No overall grade; measurements only	Yes — princess, emerald, oval, cushion, radiant
Fluorescence	None → Very Strong + colour	None → Very Strong + colour
Clarity plot	Hand-drawn inclusion map on the full report	Inclusion map on AGS Platinum reports (legacy)
Origin opinions	Country opinion on selected colored stones	N/A — diamonds only
Lab status (2026)	Active; sole standard-setter	Closed late 2022; science continues as AGS Ideal Report supplement
Trade shorthand	"Triple Ex" = Excellent cut, polish, symmetry	"AGS 000" or "AGS 0" = top tier across all three

Line-by-line: how the two reports actually differ

A side-by-side of the same round brilliant on a GIA report and an AGS Platinum report (pre-2022), or on a 2026 GIA report with the AGS Ideal supplement attached, surfaces four substantive differences worth knowing before money moves.

1. Cut grade vocabulary. GIA prints Excellent / Very Good / Good / Fair / Poor. AGS prints 0 / 1 / 2 / 3 / 4 / 5+. There is no clean one-to-one map: a GIA Triple Excellent might be AGS 0 or AGS 1 or even AGS 2 depending on what the ray-tracer shows, because the GIA bucket is wider than the AGS step.

2. Light-performance verdict. The AGS report (and the AGS Ideal supplement) prints an ASET image alongside the numeric grade. GIA reports do not include an ASET image; the cut grade is the entire light-performance statement on the GIA report unless the AGS Ideal supplement is attached.

3. Clarity plotting. GIA includes a hand-drawn inclusion plot on the full Diamond Grading Report (not the abbreviated Dossier). Pre-2022 AGS Platinum reports included an inclusion plot as well. The plotting conventions — red for inclusions, green for surface features such as polish lines and naturals — are essentially identical between the two labs, because both follow the same GIA-derived clarity grading vocabulary. Substantive trade-off: GIA Dossiers (for smaller stones) omit the plot entirely, while a full GIA report or an AGS Platinum report carries one.

4. Fluorescence. Both labs grade None / Faint / Medium / Strong / Very Strong and both report the response colour (overwhelmingly blue, occasionally yellow or white). The reporting itself is interchangeable. The substantive fluorescence call — whether Medium or Strong blue actually hurts a stone's daylight appearance — is covered in the diamond fluorescence guide and is independent of the lab name on the report.

5. Colored gemstones and origin. AGS Laboratories was a diamond lab. Country-of-origin determinations on rubies, sapphires, emeralds, and Paraiba tourmalines are issued by GIA (country opinion), SSEF and Gübelin (Swiss tier), and AGL and GRS. If someone shows you an "AGS" report on a sapphire, it isn't one — the stone's paper is either misidentified or fabricated.

The buyer's framework: when each lab matters

Stripped to dollars, the decision tree is short.

Round natural under roughly $4,000 total spend. A clean GIA report (D–J, VS2 or better, Triple Excellent) is enough. The AGS Ideal supplement isolates a top tier you can't easily see at this size, and the $25 cost plus the trade premium it earns are out of proportion to the spend.
Round natural $4,000–$15,000. Add the AGS Ideal supplement. The cut premium is meaningful relative to the total ticket, the AGS 0 verdict isolates a visibly better-performing stone under spot lighting (the type of light most engagement rings actually live under), and trade resale buyers will pay a 3–7% premium for the verified supplement.
Round natural above $15,000. Add the supplement and read the ASET image, not just the grade. At this spend level the gap between AGS 0 and AGS 1 is real money and the image itself shows you what the stone is doing.
Any round marketed as "super ideal" or "true hearts and arrows". The AGS Ideal supplement is what verifies the marketing copy. Without it, the "super ideal" claim rests on the seller's in-house cut analysis, which is not an independent credential.
Lab-grown round in 2026. The AGS Ideal supplement is the single most defensible cut credential left on the GIA lab-grown report, because GIA itself dropped granular 4Cs from the document in October 2025. See the lab-grown resale value guide for why this matters to total cost of ownership.
Fancy shape. If the stone is a princess, emerald, oval, cushion, or radiant and the seller has the AGS Ideal supplement, the supplement is worth more here than on a round — because GIA does not print an overall cut grade on fancy shapes at all. AGS is the only independent cut-grade verdict available.
Pre-2022 standalone AGS Platinum report. Valid document. The AGS 0 verdict still means what it meant when issued. To informed trade buyers the paper holds full parity with GIA; to general retail buyers post-closure the paper may absorb a 5–10% discount, which is when sellers commonly pull a fresh GIA report and add the supplement to recover value.

Resale impact, with real numbers

For a 1.00 ct round, GIA G/VS1 Triple Excellent, retail comp $7,500/ct:

GIA report only: $7,500/ct comp band.
GIA + AGS Ideal 0 supplement: $7,725–$8,025/ct (3–7% cut premium).
Pre-2022 standalone AGS Platinum 0 report at a non-trade retailer: $6,750–$7,125/ct (5–10% paper-unfamiliarity discount).
Pre-2022 standalone AGS Platinum 0 report sold to a trade buyer who knows the credential: $7,500/ct, full parity with GIA.

For the live per-carat picture those numbers anchor against, the 2026 diamond price-per-carat index carries the current bands across all popular spec combinations.

What to ask at the counter

"Which lab graded this, and may I see the full report — not just the inscription number?"
"Is the AGS Ideal cut supplement attached? If not, can one be pulled for this stone before purchase?"
For a pre-2022 AGS Platinum report: "What is the report number? Let's verify it against the AGS Laboratories historical database now archived at agslab.com."
"Does the report number laser-inscribed on the girdle match this paper?" Verify the GIA number on GIA Report Check before money moves.
For any round marketed as branded "super ideal": "Show me the AGS 0 verification, not the brand's internal cut report."

The one-line summary

GIA Excellent is a measurement bucket; AGS 0 is a light-performance verdict; the difference between them is the difference between a well-proportioned round and a round that actually performs — and in 2026 you can get both verdicts on a single GIA + AGS Ideal report for about $25 extra. The closure of AGS Laboratories changed which paper you can get standalone, not which grading philosophy the trade still respects.

Read alongside

AGS vs GIA: side-by-side grading rubric and resale impact — the article spoke that pairs with this hub.
GIA vs IGI vs AGS — the three-lab buying decision that adds IGI to the picture.
How to read a GIA diamond report — line-by-line walkthrough of the document the AGS Ideal supplement attaches to.
Diamond cut grade explained — the foundational reading on what a cut grade is and isn't.
Diamond fluorescence explained — the fluorescence-vs-daylight call that is independent of GIA vs AGS.
Lab-grown diamond resale value in 2026 — why the AGS Ideal supplement matters more on lab-grown stones after the October 2025 GIA report change.
Diamond and gemstone lexicon — anchor-linked glossary covering ASET, AGS Performance Grading Standard, Triple Excellent, and the rest of the grading vocabulary used here.