How to read a gemstone lab report

Why it matters

The report is half the value

Two rubies can look identical and differ in price many times over, because one is unheated from Burma and the other is heated from somewhere else. You can’t see that with your eyes. The laboratory report is how the market knows.

For fine coloured stones, four laboratories carry the most weight in the trade: SSEF and Gübelin in Switzerland, GRS (GemResearch Swisslab) and AGL (American Gemological Laboratories) in New York. Every important stone we sell comes with at least one of them. This guide explains how to read them, and where they differ in ways that matter for price.

Interactive

Anatomy of a report

Every lab lays its report out differently, but the information is much the same. Tap any line of this example to see what it means and what to check.

Gemmological Report

No. 00000000 · 12 March 2026

Illustrative example,
not a real report

Interactive

Decode the treatment line

This is the most important line on the report, and each lab words it differently. Pick a lab and the wording you see on your report:

For emeralds, Gübelin dropped its “insignificant” category on 1 November 2025: stones that would have been “insignificant” are now reported as having no indications of clarity enhancement.5

Colour terms

“Pigeon’s blood” and “royal blue” are not the same at every lab

The most famous colour terms in the market, pigeon’s blood for ruby and royal blue for sapphire, add serious value. But the labs award them under different rules, and the trade knows it.

GRS

How GRS grades colour

GRS first grades the colour, then, if the stone qualifies, adds a “GRS type” colour term after it: “pigeon’s blood” for ruby and “royal blue” for sapphire.2 For blue sapphire, this is how the ladder reads, from light to dark, and how the trade sees each step:

Ruby follows the same idea: “intense to vivid red” at the lighter end, “vivid red” at the heart of the range and “vivid to deep red” at the richer end, each of which can carry the GRS type “pigeon’s blood” if the stone qualifies. Gübelin has also started using “cornflower blue” on its reports.14

• The colour grade can be given without the type term, so “vivid red” alone is not the same as “vivid red, GRS type pigeon’s blood”.
• A ruby that looks the part but lacks strong fluorescence (typical of Mozambique) can still receive the term, marked with an asterisk and explained in an appendix on page two.
• For emerald, GRS issues “Old Mine / Muzo green” as an appendix.
• GRS introduced the terms on reports in the late 1990s, trademarked them in 2015 and added the “intense to vivid” and “vivid to deep” bands in 2017.

GRS’s treatment codes run from “No indication of thermal treatment” through H, H(a), H(b), H(c) and H(d). Use the decoder above to read them.

Gübelin

The Gübelin Gemstone Rating

In November 2020 Gübelin introduced a points-based rating for coloured gemstones, created because the trade had “no common language to uniformly assess colored gemstones”.7 It scores three things:

The result is expressed in Gübelin Points. Only stones scoring 75 or more receive a rating, issued as a separate Rating Document alongside the Gübelin report.8 Move the slider to see the tiers:

Gübelin’s own treatment wording for untreated ruby and sapphire is “no indications of heating”, and for colour terms its reports note that the colour “may also be called ‘pigeon blood red’” (or “royal blue”) “in the trade”.

AGL

AGL’s Prestige report

AGL in New York is known for grading coloured stones in unusual detail. Its Prestige report, the booklet, can add quality grades that the Swiss labs don’t give.9 In our experience AGL only states colour terms such as “royal blue” when you take the Prestige booklet, and for the most prestigious stones it adds an AGL Classic™ call such as “Classic Burma”, “Classic Kashmir” or “Classic Ceylon”.10

Origin

Origin is an expert opinion

No lab can “prove” where a stone was mined. Origin is an expert opinion, based on the stone’s inclusions, trace-element chemistry and spectroscopy, compared against the lab’s reference collection of stones of known origin.4 The leading labs are very good at it, but occasionally two labs disagree, and that is exactly why the most important stones often travel with two or three reports. When the 27.68 ct Jewel of Kashmir sapphire was sold, it carried reports from AGL, Gübelin and SSEF, all confirming Kashmir and no heat.11

Interactive

Check a report is genuine

Forged and altered reports exist. Every serious lab lets you check a report against its own records. Always do it for an important purchase.

Before you buy

Red flags on a report

• A lab nobody has heard of. A report is only as good as the lab behind it. For fine stones, expect SSEF, Gübelin, GRS or AGL.
• An old report. A stone can be treated after it was tested. Auction houses flag reports more than a few years old for a reason; for an important stone, ask for a recent one or an update.
• Details that don’t match. Weigh and measure the stone. Weight, measurements, shape and photo should match the report exactly.
• A colour term without the lab’s name. “Pigeon’s blood” from SSEF or Gübelin is not the same as a GRS type, so know which one you are being sold.
• No treatment line. If the report is silent on heating or oil, ask why.
• A mounted stone. Some tests are limited when a stone is set; SSEF issues its full gemstone report and colour terms only for loose stones.