Why Laboratory Certification Matters for Coloured Diamonds and Gemstones

By the Byrex Gems team, Toronto · Published 25 September 2026

What a laboratory report proves, how treatments and origin are disclosed, how GIA grades fancy colour diamonds, and a practical checklist for reading any report before you buy.

Two stones can look identical across a counter and still differ many times over in value. One may be natural and untreated, another heated, a third filled with glass, and a fourth grown in a factory. A trained eye can suspect these differences, but proving them usually takes a laboratory with spectrometers, reference collections and decades of data. This article explains what a laboratory report actually establishes, how treatments are disclosed, how GIA grades fancy colour diamonds, and how a report affects both price and how easily a stone can be resold.

Natural, synthetic or treated: the first questions

Every serious report first answers two questions. Is the material natural or laboratory-grown? Has it been treated? Laboratory-grown ruby, sapphire, emerald, alexandrite and diamond all exist, and many can only be separated from natural stones with laboratory instruments. GIA's colour-stone identification report, for example, states whether a stone is natural or laboratory-grown, identifies the species and lists detectable treatments (GIA).

Treatments vary widely in how permanent they are. GIA considers heating of sapphire and ruby permanent under normal conditions. Fracture fillers can be damaged by heat and chemicals. Some irradiated colours can fade. Surface coatings can wear at facet edges. GIA notes that sellers are legally required to disclose treatments (GIA gem treatments).

The treatments that matter most

Heating
Typical gems: Ruby, sapphire, tanzanite, aquamarine
How laboratories report it: SSEF: "indications of heating"; GRS: code H
Durability notes: Considered permanent

Heating with residues (flux or borax)
Typical gems: Ruby, sapphire
How laboratories report it: GRS: H(a) to H(c); SSEF: minor, moderate or significant residue in healed fissures
Durability notes: Residues sit in healed fissures

Lead-glass filling
Typical gems: Lower-grade ruby
How laboratories report it: GRS: H(d), "composite ruby"; LMHC information sheet 3
Durability notes: Glass can be etched by mild acids such as lemon juice

Lattice (beryllium) diffusion
Typical gems: Sapphire, ruby
How laboratories report it: GRS: H(Be); confirmed by chemical analysis
Durability notes: Shallow colour can be lost on re-cutting

Oil, wax or resin in fissures
Typical gems: Emerald, some other gems
How laboratories report it: Degree scales (see below)
Durability notes: Fillers can dry out or be removed

Irradiation, HPHT, coating
Typical gems: Diamond
How laboratories report it: GIA: origin of colour "treated"
Durability notes: Coatings can scratch; some colours are unstable

Lead-glass-filled rubies were first flagged by the GAAJ laboratory in Japan in early 2004. GIA later showed they can be recognised under the microscope by flash effects and gas bubbles, and that the glass reacts readily with solvents (G&G, Spring 2006). Beryllium diffusion became a major issue around 2001. It first appeared in orange to orangy pink "padparadscha-like" sapphires and was later found across the full range of corundum colours. Some stones can only be identified by costly mass spectrometry (G&G, Summer 2003).

Emerald clarity enhancement: whose scale?

Most emeralds are clarity-enhanced. Filling fissures with oil, wax or resin is the most common emerald treatment (GIA 4Cs). The degree of enhancement is usually the most important line on an emerald report, but laboratories word it differently:

LMHC (shared by GIA, Gübelin, SSEF, GIT, CGL, CISGEM, DSEF)
Terms used: F1 minor, F2 moderate, F3 significant for fissures; C1 to C3 for filled cavities; "no indications of clarity modification" when none is found

GIA
Terms used: F1 (minor), F2 (moderate), F3 (significant)

SSEF
Terms used: Minor, moderate or significant amount of oil (or artificial resin, etc.) in fissures; insignificant amounts not reported

GRS
Terms used: None, insignificant, minor, minor to moderate, moderate, prominent

AGL
Terms used: Insignificant, minor, moderate and higher, with the filler identified where possible

Sources: LMHC sheet 5, GIA, SSEF, GRS, AGL. The same word can sit at different points on different scales, so "minor" on one report is not automatically equal to "minor" on another.

Origin and its effect on value

Laboratories judge geographic origin from inclusions, trace-element chemistry (often measured by LA-ICP-MS), spectroscopy and comparison with reference stones of known source. GIA stresses that origin is an analytical opinion. Where two deposits formed in similar geology, their stones can be almost impossible to separate. Blue sapphire and some rubies are harder to place than emerald or Paraíba-type tourmaline (G&G, Winter 2019).

Origin still moves prices. GIA notes that Kashmir sapphires command the highest premium, while Myanmar, Sri Lanka and Madagascar also produce top-quality gems, and that origin matters most for the finest stones (GIA). Copper-bearing tourmaline with a laboratory-documented Paraíba origin also commands a premium (GIA). Origin never replaces quality. A mediocre stone from a famous locality remains a mediocre stone.

Fancy colour diamonds: how GIA grades them

The D-to-Z scale for white diamonds measures the absence of colour. Fancy colour grading describes the presence of colour through three attributes: hue (the colour itself), tone (how light or dark it is) and saturation (how strong it is). GIA recognises 27 hues. Graders assess the stone face-up, comparing it with reference stones under controlled lighting in a Macbeth Judge II light box (GIA 4Cs; GIA 4Cs). The present system was refined in the mid-1990s.

In order of increasing colour strength, GIA's descriptors are Faint, Very Light, Light, Fancy Light, Fancy, Fancy Intense, Fancy Vivid, Fancy Dark and Fancy Deep. Fancy Intense and Fancy Vivid generally command higher prices (GIA). The colour name can include modifiers. In "Fancy Intense purplish Pink", pink is the dominant hue and purplish is a secondary modifier. Because each part of the name reflects a separate judgement, read the full colour description rather than the intensity word alone.

Just as important is the origin of colour. A natural green can be imitated by irradiation, and brown or pinkish-brown diamonds can be altered by high-pressure, high-temperature treatment (G&G, Winter 2018). A GIA coloured diamond report states whether the colour is natural or treated, and natural colour carries the value. Some reports and supplementary services also give the diamond type. More than 95% of natural diamonds are type Ia, which makes the chemically pure type IIa diamonds comparatively rare (G&G, Summer 2009).

Security features and online checks

Major laboratories build security into their paper documents and keep their results in a database. GIA reports carry a hologram, security screen and microprint, and can be checked with Report Check. GRS reports carry a QR code that links to its verification page. SSEF reports can be verified at myssef.ch. Many diamonds are laser-inscribed with the report number (GIA; GRS). An online match proves the report is genuine. Measurements and weight then tie the report to the stone in front of you.

How a report affects price and liquidity

Recognition. Stones with reports from widely recognised laboratories are easier to price and resell. When RapNet stopped listing EGL-graded diamonds from October 2014 over grading inconsistency, it showed how quickly a laboratory's standing can affect the marketability of the stones it grades (National Jeweler).
Treatment status. For rubies, sapphires and emeralds, "no indications of heating" or "no clarity modification" on a respected report is often the single biggest value factor after colour. Untreated fine emeralds command higher prices (GIA 4Cs).
Origin and colour terms. An origin opinion, or a colour term such as pigeon's blood or royal blue, can widen the market for a stone. The criteria differ between laboratories, however (GRS accepts heated stones, SSEF and Gübelin do not), so experienced buyers read the conditions behind the term.
Two reports. Important stones often carry reports from two laboratories. Agreement between them reassures buyers. Disagreement needs explaining.
Currency. Old reports may predate modern detection methods, especially for beryllium diffusion and some diamond treatments. Updating the report of an important older stone is often worthwhile.

Reading a report: a practical checklist

Laboratory and report number
What it means: Who issued the opinion
What to check: Full laboratory name; verify the number online

Date
What it means: When the stone was examined
What to check: Older reports may predate current tests; fillers can change over time

Identification / species / variety
What it means: What the stone is, and natural or synthetic
What to check: "Natural" should be stated clearly, for example "natural corundum"

Weight, shape and measurements
What it means: The physical fingerprint of the stone
What to check: Match them to the stone; weigh and measure it

Colour
What it means: Descriptive colour or grade
What to check: For diamonds, the GIA grade and modifiers; for gems, whether a trade term applies and under whose rules

Origin of colour (diamonds)
What it means: Natural or treated colour
What to check: Must read "natural" for a natural-colour price

Treatment / comments
What it means: Heating, residues, fillers, diffusion
What to check: The exact wording and degree, for example F1, minor or H(a)

Geographic origin
What it means: The laboratory's opinion of the source country
What to check: Worded as an opinion; compare with any second report

Appendix or annex
What it means: Extra pages for colour terms or exceptional stones
What to check: That the appendix belongs to the same report number

Inscription and photograph
What it means: Links the document to the stone
What to check: Read any girdle inscription under magnification

For any stone with a laboratory report, email info@byrex.com or send a WhatsApp message to +1 (437) 450-3786 and we will go through the details with you.