Laboratory testing and report wording

CIBJO laboratory protocol

Required test methods are listed, which shall be applied to correctly identify the gem material stated. The listed test method is mandatory, unless a remark indicates otherwise. Definitions of the test methods are listed under 6.3. and the indicated key references on which the protocol is based, are given under 6.4.

The source lists references under each table and collects them in Appendix A; they are not reproduced here.

Source

CIBJO Blue Book — Gemmological Laboratories Book (Gemmological Commission 2024-1)

Clause 6 (Test method protocol), introduction, p.17

Test methods: definitions

Definitions from §6.3 of the source, quoted as printed (except §6.3.26, where we note a printing error in the source).

Origin determination and its limits explains how trace-element methods such as LA-ICP-MS and EDXRF are used to compare a stone with reference databases for known localities. How gemmology became a technical discipline tells how these instruments came into gem testing.

§6.3.1 Clarity enhancement check/extent, p.63

Detection of filling of fissures and/or wide fractures and cavities with oils, resins, or any other filler, and an estimation of the extent of this treatment (e.g., none/ insignificant, minor, moderate, or significant).

§6.3.2 Colour call, p.63

Precise colour description is required, for instance to make sure a colour-change is present, or to establish whether a sapphire may be called Padparadscha.

§6.3.3 Chelsea colour filter, p.64

A filter that only transmits deep red and yellow-green light.

§6.3.4 DiamondView, p.64

The DiamondView instrument illuminates a diamond with intense short-wave ultra-violet radiation and detects the surface fluorescence that is caused. Fluorescence and Phosphorescence images, showing clear growth patterns, are projected on a computer screen.

§6.3.5 Dichroscope, p.64

An instrument that allows to detect whether a gemstone shows pleochroism and, if it does, to observe the pleochroic colours side by side, for easy comparison and description.

§6.3.6 EDXRF chemistry, p.64

Energy-dispersive X-ray fluorescence is a technique whereby a sample is targeted by a high-energy X-ray beam, causing its chemical elements to fluoresce with a spectrum of lower-energy X-rays, each peak being characteristic of a chemical element. The relative concentrations of elements are indicated by the fluorescent X-ray peak intensities.

§6.3.7 FTIR(-NIR) spectroscopy, p.64

Accurate measurement of absorption or transmission positions, and their relative intensities in the (near-)infrared range of the electromagnetic spectrum. The resulting spectra are measured and digitally recorded by a Fourier Transform Infrared spectrometer. “Fourier Transform” is a mathematical technique used to convert the spectrometer signal into a spectrum plotted as a function of energy. The measurements can be done in different modes, such as e.g., transmission, diffusion reflectance, or by using KBr pellets.

§6.3.8 Hydrostatic weighing, p.64

The method used to measure the specific gravity (SG) of a gemstone. It is based on the principle of Archimedes, comparing the weight of an object in air (A) with the weight of that object in water (W). The SG can then be calculated: SG = A/(A-W).

§6.3.9 Immersion, p.64

A gemstone is immersed in a liquid with a similar refractive index to observe features that are otherwise not or less visible, for instance colour distribution or zoning.

§6.3.10 LA-ICP-MS Chemistry, p.64

Laser Ablation Inductively Coupled Plasma Mass Spectrometry is an analytical technology that enables highly sensitive elemental and isotopic analysis to be performed directly on solid samples. LA-ICP-MS begins with a laser beam focused on the sample surface to generate fine particles – a process known as Laser Ablation. The ablated particles are then transported to the secondary excitation source of the ICP-MS instrument for digestion and ionisation of the sampled mass. The excited ions in the plasma torch are subsequently introduced to a mass spectrometer detector for both elemental and isotopic analysis. It is not entirely non-destructive, but can perform ultra-highly sensitive chemical analysis down to ppb (parts per billion) level.

§6.3.11 Microradiography, p.65

The process of taking a photograph of an object by using X-rays, showing minute internal structure.

§6.3.12 Microscope, p.65

A gemmological microscope is a stereo binocular microscope with good depth of vision and field of view, with generally magnification varying in between 10x and 80x. Research microscopes with much higher magnification power may be used as well in gemmological laboratories.

§6.3.13 Phenomena, p.65

Detection of phenomena, such as colour-change of a gemstone, when viewed in different light conditions, play of colour, labradorescence, reflection of light by inclusions causing chatoyancy (Cat’s-eye), asterism (Star), aventurescence, adularescence; inclusion patterns causing the trapiche effect, bloodshot effect.

§6.3.14 PL spectroscopy, p.65

Detection of photoluminescence (light emission) of an object illuminated by a laser. Light emission occurs after the excitation by photons (electromagnetic radiation). Different lasers may be used, for example red (633 nm), green (514 and 532 nm), blue (488 nm) and UV (250 nm) lasers. For diamonds, PL is usually performed at low temperature (- 196 ̊C)

§6.3.15 Pleochroism, p.65

A property of doubly refractive coloured gemstones of absorbing light to an extent that depends on the vibration direction of the polarised light rays. The effect causes two different colours (dichroism) or three different colours (trichroism), depending on the type of gemstone. These different colours may be seen when viewing a gemstone from different directions under transmitted light.

§6.3.16 Polariscope, p.65

A polariscope is an instrument with two polarising filters fitted one above the other in a fixed crossed position, meaning that the transmitted vibration direction of polarisation of the upper filter is at right angles to that of the lower filter. The filters are either fixed on an inbuilt light or placed on a separate light source.

§6.3.17 Raman spectroscopy, p.66

Detection of an extremely slight shift of energy of the light or radiation scattered on the surface of an object illuminated by a laser. The resulting re-emitted spectrum, or Raman spectrum, is characteristic for different (solid or fluid) substances, and allows rapid identification, also if they are enclosed within another transparent substance. Different lasers may be used, for example near-infrared (780 nm), red (633 nm), green (514 and 532 nm), blue (488 nm) and UV (250 nm) lasers.

§6.3.18 Refractometer, p.66

The gemmological refractometer is designed to measure the refractive index or indices of a gemstone. It makes use of total internal reflection of monochromatic light, going through an in-built special type of glass, which is in contact with a flat, polished surface of a gemstone.

§6.3.19 Refractive index, p.66

A simple relationship between the light’s angle of incidence and angle of refraction (the amount of bending), when it reaches and enters a gemstone. The slower the light’s speed in a material, the greater the bending effect, thus the higher the refractive index. Depending on the structure of the material, light will remain as a single ray or be split into two rays; the effects are called “single refraction” (giving one refractive index), and “double refraction” (giving two refractive indices, with a minimum and maximum value).

§6.3.20 Residue check/ extent, p.66

Detection of residue in healed fissures and/or filled cavities as a result of heat-treatment, and an estimation of the extent of this treatment (e.g., none/ insignificant, minor, moderate, or significant).

§6.3.21 Spectroscope, p.66

A spectroscope is essentially a tube with a narrow slit at one end and a lens at the other, with in between an arrangement of optically connected prisms, or a diffraction grating, creating a spectrum - spectral colours of white light that enters the slit and are spread out by the prisms or grating and can be viewed through the lens.

§6.3.22 Long-wave UV fluorescence, p.66

Emission of visible light by a substance when excited by long-wave ultraviolet radiation (principal wavelength of 365 nm), produced by a UV-lamp.

§6.3.23 Long-wave UV phosphorescence, p.66

Continued emission of visible light by a substance after excited by long-wave ultraviolet radiation (principal wavelength of 365 nm), produced by a UV-lamp.

§6.3.24 SEM-EDS, p.66

Scanning Electron Microscopy with Energy Dispersive X-Ray microanalysis is a technique, using an electron beam to scan the surface of an object. Scattered electron reflections are detected at very high magnification which are displayed as black-and- white images on a screen. Elemental analysis and mapping can be obtained, as the electrons also cause the object’s chemical elements to emit a spectrum of X-rays, each peak being characteristic of a chemical element.

§6.3.25 Short-wave UV fluorescence, p.67

Emission of visible light by a substance when excited by short-wave ultraviolet radiation (principal wavelength of 254 nm), produced by a UV-lamp.

§6.3.26 Short-wave UV phosphorescence, p.67

As printed, the definition repeats the long-wave wording (365 nm); the short-wave counterpart would be 254 nm (see §6.3.25).

§6.3.27 Specific Gravity, p.67

The ratio of the weight of a substance to the weight of an equal volume of water.

§6.3.28 UV-Visible(-NIR) spectroscopy, p.67

Accurate measurement of absorption or transmission positions, and their relative intensities in the UV, Visible light (and near-infrared) range of the electromagnetic spectrum. The resulting spectra are measured and digitally recorded by a UV-Visible(- NIR) spectrometer.

§6.3.29 X-Ray CT scan, p.67

X-Ray computed tomography makes use of computer-processed combinations of many X-ray images taken from different angles around a single axis of rotation, to produces cross-sectional (tomographic) images (virtual “slices”) of specific areas of a scanned object, allowing the user to see inside the object without cutting. Digital geometry processing is used to generate a three-dimensional image of the inside of the object.

§6.3.30 XRD, p.67

X-Ray Diffraction is a scattering of X-rays by the atoms of a crystal that produces an interference effect so that the diffraction pattern gives information on the structure of the crystal or the identity of a crystalline substance. One of two primary types of XRD analysis (X-ray powder diffraction and single-crystal XRD) is commonly applied.

Methods used in the tables but not defined in §6.3: LA-ICP-MS or SEM-EDS chemistry, Raman/PL spectroscopy, Geiger counter, Geiger counter or dosimeter (µS/h), Safe storage, Magnet (magnetic reaction).

Test protocol by gem material

One row per protocol table in the source (§6.1 gemstones, §6.2 pearls and organic materials). Entries on this site link to the material; rows for materials without an entry here are listed as well.

† The source adds a general condition to this test, such as “If other tests are inconclusive”, in several wordings; it is not repeated in each cell.

Inconsistencies in the source

§6 (introduction)

The introduction says the key references are given under “6.4”, but the book has no §6.4; references sit under each table and are collected in Appendix A.

§6.3.26

The definition of short-wave UV phosphorescence repeats the long-wave wording (365 nm) word for word, identical to §6.3.23.

§6.2.22 / p.61

Between §6.2.22 and §6.2.23 there is an unnumbered table “Pearl (Pleuropoca species)”; the genus is spelled as printed.

§6.2.22

The Special attention line ends in “damage by” and is not finished (the next, unnumbered table follows directly).

§6.1.18

The Phenomena remark “Cat’s-eye (colour change (alexandrite cat’s-eye)” has unbalanced brackets; reproduced as printed.

§6.1.30

The method is written “LA-ICP-MS spectroscopy”, while §6.3.10 defines “LA-ICP-MS Chemistry”: one method, two names.

§6.1.29 / 6.1.23 / 6.1.41

Geiger counter / dosimeter, Safe storage and Magnet are used in the tables but have no definition in §6.3.

§6.1.36

The Forsterite table splits “Refractometer (refractive index)”, “dichroscope” and “spectroscope” into three lower-case lines; reproduced as printed.

What every report states (LMHC #0)

Every detected treatment goes on the front of the report; the sheet also acknowledges that some heating and irradiation cannot yet be detected (for example in some tourmaline, tanzanite, aquamarine and topaz), and reports state that findings are the laboratory's opinion, not a valuation.

Wording on the report: All detected treatments shall be featured on the front of reports.

Source

LMHC Information Sheet #0, Version 2, November 2018: p.2 (Information Sheet #0, version 2, November 2018)

Entries this applies to:

• Tourmaline
• Tanzanite
• Aquamarine
• Topaz

Treatment pages for this sheet: Heated / Heat-treated, Irradiated

When colour authenticity cannot be determined (LMHC #8)

For stones that are often heated or irradiated but where treatment cannot be established (beryl, quartz, spodumene, topaz, tourmaline, zircon, zoisite and others), reports name the stone as usual and add a line like this.

Wording on the report: Colour authenticity is currently undeterminable

Source

LMHC Information Sheet #8, Version 6, January 2023: p.1 (Information Sheet #8, version 6, January 2023)

Entries this applies to:

• Beryl
• Aquamarine
• Morganite
• Heliodor / Golden Beryl
• Demantoid
• Quartz
• Amethyst
• Citrine
• Smoky Quartz
• Spodumene
• Kunzite
• Topaz
• Tourmaline
• Zircon
• Zoisite
• Tanzanite

Treatment pages for this sheet: Heated / Heat-treated, Irradiated

Colour-change stones (LMHC #9)

Colour-change stones get both colours, in daylight and in incandescent light, on the report, with “colour-change” before the species or variety name; the light source and viewing distance for the judgement are the same as for alexandrite.

Wording on the report: colour-change [Species/Variety]

Source

LMHC Information Sheet #9, Version 4, February 2023: p.1 (Information Sheet #9, version 4, February 2023)

Entries this applies to:

• Colour-Change Garnet
• Colour-change Sapphire
• Diaspore

Organic fillers in other gemstones (LMHC #12)

For stones other than corundum and emerald, oil, resin or wax in fissures or cavities is reported this way and graded from minor to significant; coloured fillers that change the colour are named.

Wording on the report: Fissure filling or indications of clarity enhancement/modification

Source

LMHC Information Sheet #12, Version 5, January 2023: p.1 (Information Sheet #12, version 5, January 2023)

Treatment pages for this sheet: Filled / Fracture-filled, Dyed, Waxed, Impregnated

Colour stability testing (LMHC #16)

After a colour stability test, reports note one of three results — no colour shift, minor colour shift or distinct colour shift — and may add that the change is reversible. It matters for stones whose colour is sensitive to light, such as padparadscha.

Wording on the report: no colour shift

Source

LMHC Information Sheet #16, Version 1, August 2025: p.2 (Information Sheet #16, version 1, August 2025)

Entries this applies to:

• Padparadscha Sapphire
• Sapphire
• Yellow Sapphire
• Pink Sapphire
• Spodumene
• Kunzite
• Sodalite
• Hackmanite
• Zircon

LMHC information sheets on report wording

The Laboratory Manual Harmonisation Committee (LMHC) publishes standard report wording as numbered information sheets. Each row links to the original PDF.

The sheets may be copied only in full; translation or abstracting needs LMHC's written consent. This site therefore shows only short quotations of the report wording with its own explanations, and links to each original.

LMHC information sheet index

lmhc-gemmology.org

Wording not itemised on entry pages

Each entry page itemises only the few LMHC wordings most common on reports. The others are listed here by entry, section and locator; the wording itself is in the linked original.

• #1 · Corundum · extent grades · p.2, Table 1 and figure captions (Information Sheet #1)
• #1 · Corundum · treatment wording · p.1, “Healed fissures” (Information Sheet #1)
• #2 · Corundum · durability note · p.1, Footnote 3 (Information Sheet #2)
• #2 · Corundum · treatment wording · p.1, Case 2 (Information Sheet #2)
• #3 · Corundum · durability note · p.2, “Corundum with/and glass (manufactured product)”, further information (Information Sheet #3)
• #3 · Corundum · durability note · p.2, “Special note” (Information Sheet #3)
• #3 · Corundum · extent grades · p.1, Table 1 (Information Sheet #3)
• #3 · Corundum · identification line · p.2, “Corundum with/and glass (manufactured product)” (Information Sheet #3)
• #5 · Emerald · optional comments · p.2, Note A (Information Sheet #5)
• #5 · Emerald · durability note · p.2, Notes E and I (Information Sheet #5)
• #5 · Emerald · identification line · p.4, “Emerald with/and resin” (Information Sheet #5)
• #5 · Emerald · treatment wording · p.3, “Indications of coloured fissure filling” (Information Sheet #5)
• #5 · Emerald · treatment wording · p.3, “Indications of cavity filling” (Information Sheet #5)
• #11 · Fei Cui / Jadeite Jade · identification line · p.2, “Definitions”, Fei Cui (Information Sheet #11)

By the numbers

Protocol tables in the source

120

Entries on this site that carry a protocol table

88

Test-method definitions

30