Filled / Fracture-filled
Fracture filling fills fissures or cavities in a gem with a foreign substance such as glass, lead glass, resin, oil or polymer. The filler must be named, and fillings can be unstable and may deteriorate or change colour over time.
On this page
Naming rule
- Naming rule
- [Filler]-filled [material name]
- Market differences and mutual recognition
- The divide here is about the filler itself. GB/T 16552 grades filling in three tiers: colourless oil or wax is an optimization, a little glass or resin in minor fissures must be annotated, and saturating porous material with lead glass or cured resin is a treatment. CIBJO's disclosure chart (§4.2.5.2) instead names oil, resin and glass fillers separately, and AGTA likewise keeps codes O and F apart.
Gem treatments compares how every treatment on this site is named and what each must disclose.
Where the treatment acts (schematic)
Fills fissures or cavities with a foreign substance (glass, lead glass, resin, oil, polymer etc.).
- Low-grade, heavily fractured corundum (ruby / pink sapphire), translucent to opaque
- Unfilled fracture (looks white)
- Powder mainly of lead and silica
- Reheating
- Lead glass in the filled fractures and cavities
If you reuse this animation, please credit LumaLark Wiki and link to this pageLicense: CC BY 4.0
Scene-by-scene transcript (4 scenes, with sources)
The caption of each scene in the animation above (the first scene lists its three panel captions), with sources.
Scene 1Fracture filling (lead-glass-filled ruby as the example)
Before: Lead-glass filling starts from low-grade, heavily fractured corundum that is translucent to opaque.
During: The stone is mixed with powders composed mainly of lead and silica and heated again, so the powders fuse into a glass that penetrates the fractures.
After: The lead glass remains in the fractures and cavities, and corundum that was translucent to opaque becomes transparent enough for jewellery.
Treated zone: fractures and cavities
Scene 2Process conditions
The stone is mixed with powders composed mainly of lead and silica and heated again, so the powders fuse into a glass that penetrates the fractures. The 2006 study relays the treater's account: the rough is first preformed to remove matrix and obvious impurities; it is then "warmed" to moderate temperatures (reportedly 900–1,400°C), which removes impurities from the fractures and may improve the colour; it is then mixed with the powders, which may also contain sodium, calcium, potassium and metal oxides such as copper or bismuth, and heated again, reportedly to approximately 900°C. The study notes that lead-glass filling initially did not involve partial healing of fractures; a 2025 laboratory information sheet adds that the process might also induce local healing of fissures.
Scene 3How it works
It works on the same principle as fracture filling in emerald and diamond: the closer the filler's refractive index is to the host's, the less visible the fractures. The silica glass used earlier has a significantly lower R.I. than corundum, so even fully filled fractures remain easy to see; the study obtained a single approximate R.I. reading of 1.75–1.76 for the lead glass in larger cavities; the filled fractures show very low relief, meaning little optical contrast with the surrounding corundum, and are far less conspicuous, though still visible with a loupe or microscope. The glass penetrates fractures as thin as 5 μm, its boundary with the ruby is sharp, and no secondary corundum had precipitated in the samples analysed.
Scene 4After treatment and how it is detected
The lead glass remains in the fractures and cavities, and corundum that was translucent to opaque becomes transparent enough for jewellery. Laboratory reports describe such stones as having glass-filled fissures (and cavities), graded minor, moderate or significant by the size and position of each filled fissure or cavity, and LMHC member laboratories have mostly seen significant amounts of glass; a heavily fractured, friable piece of rough infused with glass and then faceted, or many unrelated small pieces bound together with glass, is reported as 'corundum with/and glass' (a manufactured product), and if the glass is altered the stone may fall into pieces. Glass-filled corundum is unstable to elevated temperatures and certain chemical agents, the lead glass in the samples studied melted between 600°C and 700°C, and unmounting the stone is recommended before jewellery repair.
These features were common in the stones of the 2006 study: under magnification, rotating the stone revealed blue flashes in the filled fractures, sometimes with orange flashes as well; almost all samples had flattened and rounded gas bubbles in the glass; and in reflected light the surface lustre of the lead glass was close to that of ruby, so even large filled cavities could be hard to find, sometimes given away only by the poorer polish of the softer glass. Glasses of other compositions can behave differently: a 2014 laboratory note describes Burmese rubies filled with a lower-lead glass that showed no flash effect and a filler lustre slightly below the host's, confirmed only by chemical analysis, so the absence of flashes alone does not rule out filling. Lead glass strongly absorbs X-rays, so X-radiography shows the filled fractures. Many of the studied stones kept unaltered rutile needles, which the authors then took to show they had not been exposed to temperatures high enough to damage rutile (given as above 1,500°C); 2022 heating experiments on Burmese ruby note that rutile silk generally begins to dissolve at around 1200–1350°C, and in their samples it showed no noticeable change after heating up to 1100°C, so intact needles cannot rule out heating at lower temperatures. The study also holds that the presence of this glass in fractures is sufficient proof that the stone has been heat treated (at least 700°C to soften the glass, and at least 800°C or 900°C for it to flow into fractures), and the LMHC report wording includes indications of heating.
Sources
- Identification and Durability of Lead Glass–Filled Rubies (S.F. McClure, C.P. Smith, W. Wang, M. Hall; Gems & Gemology, Spring 2006, Vol. 42, No. 1, pp. 22–34)
- LMHC Information Sheet #3, Version 10, May 2025
- Lead-Glass-Filled Burmese Rubies, by Najmeh Anjomani and Rebecca Tsang (Lab Notes, Gems & Gemology, Winter 2014, Vol. 50, No. 4, pp. 296–297; Lab Notes section PDF pp. 293–301)
- A Canary in the Ruby Mine: Low-Temperature Heat Treatment Experiments on Burmese Ruby, by E. Billie Hughes and Wim Vertriest (Gems & Gemology, Winter 2022, Vol. 58, No. 4, pp. 400–423)
How the naming authorities record it
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| Column | Value |
|---|---|
| Description | Fills fissures or cavities with a foreign substance (glass, lead glass, resin, oil, polymer etc.). |
| GIA code | F; Resin-filled; Glass-filled; Oil-filled |
| LMHC number / note | F / RES / O (CIBJO Gemstone Book 2022 Annex B, clause 7.2: Filling / Fissure filling with resin / Fissure filling with oil); LMHC IS3 (corundum glass-filled fissures only), IS5 (emerald fissure filling only), IS12 (organic fillers, general but explicitly excludes what IS1/IS3/IS5 already cover) |
| GB/T category | GB/T 16552-2017 §5.4.1 Table 1: filling has three tiers - colourless oil/wax filling (including minor resin filling of emerald as clarity optimization) is optimization with no remark; glass or synthetic-resin filling of minor fissures and cavities is optimization (annotation required); saturating porous, heavily fissured material with Pb- or Bi-bearing glass or cured synthetic resin is treatment. Representation method: optimization at §5.4.2.1, treatment at §5.4.2.2 - the name must carry the treatment method or the word “treated” before or after it; the standard does not require the filler substance to be named. |
| CIBJO disclosure requirement | CIBJO Gemstone Book 2022 §5.44 defines Impregnation. CIBJO Gemstone Book 2022 §5.56 defines Oil. CIBJO Gemstone Book 2022 §4.2.5.2 sets out the disclosure method (trade codes F / RES / O per Annex B, clause 7.2). |
| FTC regulatory citation | §23.24 general rule: disclosure is required if the treatment is not permanent (a), creates special care requirements (b), or has a significant effect on value (c). §23.24 names no individual treatment, so Part 23 does not say which of (a)–(c) fracture filling meets. |
| RAL / German declaration | No public source text: RAL 560 A5 is a paid document not on file on this site, so no RAL/DGemG wording is shown (unchecked) |
| JJA/AGL (Japan) treatment disclosure | JJA/AGL 2025 §1-2-1 lists impregnation (item ②) and filling (item ⑧) among the treatments applied to natural stones; §2-1-1: the treatment is to be stated to the extent it can be known. |
| AGTA code | F — filling of surface-reaching cavities or fissures with glass, plastic, borax or similar colourless solids; O — oiling/resin infusion of fissures with colourless oil, wax, resin etc., glass and plastic excluded (GIM 17th ed., p.V). The 17th edition has no G-F / R-F / O-F sub-codes. Consumer disclosure must be in plain language; codes alone are not sufficient (p.III). |
| Gem-A position | The Gem-A By-Laws have no filling-specific rule. §7.e.iii: before purchase the buyer should be told if the stone is known to have been treated and, where relevant, how that may affect its durability; §7.b: CIBJO guidelines and definitions are taken as best practice. |
| Naming rule | [Filler]-filled [material name] |
| Disclosure requirement | Name the filler (resin, oil, polymer, glass or lead glass) and bear in mind that fillings can be unstable and may deteriorate or change colour over time. LMHC Information Sheet #3 treats corundum with glass in two ways: glass in fissures or cavities is still reported on natural corundum as a filling, and only a badly fractured single piece infused throughout, or small fragments bound together with glass, is reported as a manufactured product. |
| Typical materials treated | Emerald (oil, resin), ruby (lead glass, resin), diamond (glass), tourmaline (resin) |
| Market differences and mutual recognition | The divide here is about the filler itself. GB/T 16552 grades filling in three tiers: colourless oil or wax is an optimization, a little glass or resin in minor fissures must be annotated, and saturating porous material with lead glass or cured resin is a treatment. CIBJO's disclosure chart (§4.2.5.2) instead names oil, resin and glass fillers separately, and AGTA likewise keeps codes O and F apart. |
Materials on which it is recorded
How lab reports word it, by material
The standard report wording (LMHC) for this treatment is set out on these entries and sections:
The laboratory testing page's LMHC index lists every LMHC information sheet on report wording.
Care after this treatment
The CIBJO Gemstone Book §6.2 names this treatment in its special care: special-care code k, special-care code l.
CIBJO definitions
- Cavity
a hollow or pitted area (a hole) within a stone reaching the surface. Also see: fissure (5.29), fracture (5.33) and fracture filling (5.34).
CIBJO Blue Book — Official Gemstone Book (Coloured Stone Commission 2022) (CIBJO): §5.12, p.21
- Filling
to introduce a substance that occupies a whole or part of a void. See clause 4.2.5.2.
CIBJO Blue Book — Official Gemstone Book (Coloured Stone Commission 2022) (CIBJO): §5.28, p.23
to introduce a substance that occupies the whole or part of a void (5.207).
CIBJO Blue Book — Pearl Book (Pearl Commission 2024-1) (CIBJO): §5.70, p.29
to introduce a substance that occupies a whole or part of a void.
CIBJO Blue Book — Coral Book (Coral Commission 2024) (CIBJO): §5.37, p.14
The books word this differently; each wording is given with its source.
- Fissure
a very narrow opening; a fine fracture.
CIBJO Blue Book — Official Gemstone Book (Coloured Stone Commission 2022) (CIBJO): §5.29, p.23; CIBJO Blue Book — Pearl Book (Pearl Commission 2024-1) (CIBJO): §5.72, p.29; CIBJO Blue Book — Coral Book (Coral Commission 2024) (CIBJO): §5.38, p.15
- Fluid
a substance of low enough viscosity that it will flow easily.
CIBJO Blue Book — Official Gemstone Book (Coloured Stone Commission 2022) (CIBJO): §5.30, p.23; CIBJO Blue Book — Coral Book (Coral Commission 2024) (CIBJO): §5.39, p.15
- Fracture
an opening larger than a fissure (5.29) a crack.
CIBJO Blue Book — Official Gemstone Book (Coloured Stone Commission 2022) (CIBJO): §5.33, p.23
An opening; a crack.
CIBJO Blue Book — Pearl Book (Pearl Commission 2024-1) (CIBJO): §5.73, p.29
an opening; a crack.
CIBJO Blue Book — Coral Book (Coral Commission 2024) (CIBJO): §5.40, p.15
The books word this differently; each wording is given with its source.
- Fracture filling
to occupy the whole or part of a fracture with a substance, e.g. glass, resins, oil, etc., to pervade; to spread throughout; to occupy completely; or to make full, with the purpose of making the fracture less visible. See clause 4.2.5.2.
CIBJO Blue Book — Official Gemstone Book (Coloured Stone Commission 2022) (CIBJO): §5.34, p.23
To occupy the whole or part of a fracture with a substance, e.g. glass, resins, oil; to pervade; to spread throughout; to occupy completely; or make full, with the purpose of making the fracture less visible.
CIBJO Blue Book — Pearl Book (Pearl Commission 2024-1) (CIBJO): §5.74, p.29
to occupy the whole or part of a fracture with a substance, e.g. resins, oil, etc., to pervade; to spread throughout; to occupy completely; or to make full, with the purpose of making the fracture less visible.
CIBJO Blue Book — Coral Book (Coral Commission 2024) (CIBJO): §5.41, p.15
The books word this differently; each wording is given with its source.
- Oil
an agent such as natural or synthetic oil which are used for fissure filling, see clause 4.2.5.2.
CIBJO Blue Book — Official Gemstone Book (Coloured Stone Commission 2022) (CIBJO): §5.56, p.26
- Permeate
the filling of fissures and/or fractures with oil, wax, resin (5.70), polymer or other fluid substances, other than glass to diminish their appearance.
CIBJO Blue Book — Official Gemstone Book (Coloured Stone Commission 2022) (CIBJO): §5.61, p.26
the filling of fissures and/or fractures with oil, wax, resin, polymer or other fluid substances, other than glass to diminish their appearance. See clause 4.2.5.1.
CIBJO Blue Book — Coral Book (Coral Commission 2024) (CIBJO): §5.76, p.19
The books word this differently; each wording is given with its source.
- Polymer
A polymer is a large organic molecule made up of chains or rings of linked repeating subunits, which are called monomers. A polymer is formed by polymerization, the joining of many monomers. Because the molecules consist of many monomers, polymers tend to have high molecular masses. (Resin is a polymer, but it’s a more specific term, describing a particular subset of polymers, see clause 5.70).
CIBJO Blue Book — Official Gemstone Book (Coloured Stone Commission 2022) (CIBJO): §5.65, p.26
- Resin
a solid to semisolid transparent to opaque organic substance such as Canada balsam.
CIBJO Blue Book — Official Gemstone Book (Coloured Stone Commission 2022) (CIBJO): §5.70, p.27
- Void
a cavity (5.12) that contains no matter.
CIBJO Blue Book — Official Gemstone Book (Coloured Stone Commission 2022) (CIBJO): §5.86, p.28
an empty space that is either entirely or partially contained within a natural or cultured pearl including a drill hole (5.64).
CIBJO Blue Book — Pearl Book (Pearl Commission 2024-1) (CIBJO): §5.207, p.46
a cavity that contains no matter.
CIBJO Blue Book — Coral Book (Coral Commission 2024) (CIBJO): §5.99, p.21
The books word this differently; each wording is given with its source.
- Oiling
a process, called ‘decraqueler’, sometimes applied to natural and cultured pearls, whereby the surface of pearls is soaked in warm oil; to diminish the appearance of cracks.
CIBJO Blue Book — Pearl Book (Pearl Commission 2024-1) (CIBJO): §5.146, p.40
filling coral fissures and/or fractures with agents including essential oils (e.g. cedarwood oil) and mineral oils (e.g. Joban oil, paraffin), to make the fissures and fractures less visible.
CIBJO Blue Book — Coral Book (Coral Commission 2024) (CIBJO): §5.71, p.18
The books word this differently; each wording is given with its source.
Definitions are quoted verbatim from the cited CIBJO Blue Book; […] marks an excerpt, and the full definition is at the cited clause.
Materials listed for this method in GB/T 16552-2017 Table B.1
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| Material (row) | Method | Effect | Category |
|---|---|---|---|
| Diamond | Filling | Improves or changes durability and appearance | Treatment |
| Ruby | Filling | Improves or changes durability and appearance | Graded — see §5.4.1, Table 1 |
| Sapphire | Filling | Improves or changes durability and appearance | Graded — see §5.4.1, Table 1 |
| Emerald | Filling | Improves or changes durability and appearance | Graded — see §5.4.1, Table 1 |
| Aquamarine | Filling | Improves or changes durability and appearance | Graded — see §5.4.1, Table 1 |
| Beryl | Filling | Improves or changes durability and appearance | Graded — see §5.4.1, Table 1 |
| Tourmaline | Filling | Improves or changes durability and appearance | Graded — see §5.4.1, Table 1 |
| Spinel | Filling | Improves or changes durability and appearance | Graded — see §5.4.1, Table 1 |
| Garnet | Filling | Improves or changes durability and appearance | Graded — see §5.4.1, Table 1 |
| Rock Crystal | Filling | Improves or changes durability and appearance | Graded — see §5.4.1, Table 1 |
| Feldspar | Filling | Improves or changes durability and appearance | Graded — see §5.4.1, Table 1 |
| Kyanite | Filling | Improves or changes durability and appearance | Graded — see §5.4.1, Table 1 |
| Calcite | Filling | Improves or changes durability and appearance | Graded — see §5.4.1, Table 1 |
| Feicui, Jadeite | Filling | Improves or changes durability and appearance | Graded — see §5.4.1, Table 1 |
| Feicui, Jadeite | Bleaching and filling | Changes appearance | Treatment |
| Nephrite | Filling | Improves or changes durability and appearance | Graded — see §5.4.1, Table 1 |
| Opal | Filling | Improves or changes durability and appearance | Graded — see §5.4.1, Table 1 |
| Chalcedony (Agate/Jasper) | Filling | Improves or changes durability and appearance | Graded — see §5.4.1, Table 1 |
| Silicified Jade (Silicified Asbestos/Silicified Wood/Silicified Coral) | Filling | Improves or changes durability and appearance | Graded — see §5.4.1, Table 1 |
| Quartzite jade | Bleaching and filling | Changes appearance | Treatment |
| Serpentine | Filling | Improves or changes durability and appearance | Graded — see §5.4.1, Table 1 |
| Charoite | Filling | Improves or changes durability and appearance | Graded — see §5.4.1, Table 1 |
| Turquoise | Filling | Improves or changes durability and appearance | Graded — see §5.4.1, Table 1 |
| Lapis lazuli | Filling | Improves or changes durability and appearance | Graded — see §5.4.1, Table 1 |
| Malachite | Filling | Improves or changes durability and appearance | Graded — see §5.4.1, Table 1 |
| Marble | Filling | Improves or changes durability and appearance | Graded — see §5.4.1, Table 1 |
| Rhodochrosite | Filling | Improves or changes durability and appearance | Graded — see §5.4.1, Table 1 |
| Fluorite | Filling | Improves or changes durability and appearance | Graded — see §5.4.1, Table 1 |
| Chicken-blood Stone | Filling | Improves or changes durability and appearance | Graded — see §5.4.1, Table 1 |
| Shoushan Stone | Filling | Improves or changes durability and appearance | Graded — see §5.4.1, Table 1 |
| Qingtian Stone | Filling | Improves or changes durability and appearance | Graded — see §5.4.1, Table 1 |
| Balin Stone | Filling | Improves or changes durability and appearance | Graded — see §5.4.1, Table 1 |
| Changhua Stone | Filling | Improves or changes durability and appearance | Graded — see §5.4.1, Table 1 |
| Sugilite | Filling | Improves or changes durability and appearance | Graded — see §5.4.1, Table 1 |
| Mica Jade | Filling | Improves or changes durability and appearance | Graded — see §5.4.1, Table 1 |
| Coral | Filling | Improves or changes durability and appearance | Graded — see §5.4.1, Table 1 |
| Amber | Filling | Improves or changes durability and appearance | Graded — see §5.4.1, Table 1 |
| Ivory | Filling | Improves or changes durability and appearance | Graded — see §5.4.1, Table 1 |
| Mammoth Ivory | Filling | Improves or changes durability and appearance | Graded — see §5.4.1, Table 1 |
JJA/AGL table entries relating to this treatment
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| Gem name | Colour | As written in the table | Entry on this site | Page |
|---|---|---|---|---|
| Boulder Opal | filling of the host rock | Boulder Opal | p.9 | |
| Rutilated Quartz | impregnation with a colourless agent | Rutilated Quartz | p.10 | |
| [inclusion] Quartz | any colour | impregnation with a colourless agent | Included Quartz | p.10 |
| Ruby | brownish red to purplish red | heating, with cavities filled by a transparent substance | Ruby | p.12 |
| [colour] Sapphire | any colour | heating, with cavities filled by a transparent substance | Sapphire | p.12 |
| Star Ruby / [colour] Star Sapphire | any colour | impregnation with a colourless agent (oil or resin) | Star Ruby, Star Sapphire | p.12 |
| Ruby + Lead Glass | red + lead glass | lead-glass impregnation | Lead-Glass-Filled Ruby | p.13 |
| [colour] Sapphire + Lead Glass | other colours + lead glass | lead-glass impregnation | Sapphire | p.13 |
| Star Ruby/Star Sapphire + Lead Glass | asterism + lead glass (as written in the colour column) | lead-glass impregnation | Star Ruby, Star Sapphire | p.13 |
| Coral | red, pink, white and others | filling | Coral, Precious Coral | p.13 |
| Coral | red, pink, white and others | filling with the same material | Coral, Precious Coral | p.13 |
| Diamond | any colour | impregnation with a colourless agent | Diamond | p.14 |
| Emerald | green (chromium) | no indication of impregnation | Emerald | p.16 |
| Emerald | green (chromium) | impregnation with a colourless agent | Emerald | p.16 |
| Emerald | green (chromium) | impregnation with a coloured agent | Emerald | p.16 |
| Emerald | green (chromium) | filling | Emerald | p.16 |
| Red Beryl | red | impregnation with a colourless agent | Red Beryl | p.16 |
Other treatments
Sources
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| Authority | Document | Version | Clause | Source |
|---|---|---|---|---|
| GB/T | GB/T 16552-2017 | 2017 | §5.4.1 | Source |
| GB/T | GB/T 16552-2017 | 2017 | Table 1 | Source |
| GB/T | GB/T 16552-2017 | 2017 | §5.4.2.1 | Source |
| GB/T | GB/T 16552-2017 | 2017 | §5.4.2.2 | Source |
| CIBJO | CIBJO Gemstone Book | 2022 | §5.44 | Source |
| CIBJO | CIBJO Gemstone Book | 2022 | §5.56 | Source |
| CIBJO | CIBJO Gemstone Book | 2022 | §4.2.5.2 | Source |
| CIBJO | CIBJO Gemstone Book | 2022 | Annex B, clause 7.2 | Source |
| FTC | 16 C.F.R. Part 23 | §23.24 | Source | |
| LMHC | LMHC Information Sheet #5 | version 6, May 2025 | Emerald fissure filling | Source |
| LMHC | LMHC Information Sheet #12 | version 5, January 2023 | Organic fillers | Source |
| JJA/AGL | JJA/AGL definitions and nomenclature for gems (Japanese-language document, no official English title) | issued January 2015, revised November 2025 | §1-2-1 | Source |
| JJA/AGL | JJA/AGL definitions and nomenclature for gems (Japanese-language document, no official English title) | issued January 2015, revised November 2025 | §2-1-1 | Source |
| AGTA | AGTA Gemstone Information Manual | 17th edition, August 2026 | p.V (F) | Source |
| AGTA | AGTA Gemstone Information Manual | 17th edition, August 2026 | p.V (O) | Source |
| AGTA | AGTA Gemstone Information Manual | 17th edition, August 2026 | p.III | Source |
| Gem-A | Gem-A By-Laws §7 Code of Practice (Gem Code) | 2009 revision | §7.e.iii | Source |
| Gem-A | Gem-A By-Laws §7 Code of Practice (Gem Code) | 2009 revision | §7.b | Source |
What the eye can and cannot tell
The description has to name the filling substance and disclose how much of it there is; CIBJO requires both.
US 16 CFR §23.25(d) does not allow a product made with a filler or binder such as lead glass to be called “ruby” or “treated ruby”, and calling it “composite ruby” requires a clear statement that it differs from the named stone and needs special care; LMHC Information Sheet #3, by contrast, keeps reporting stones whose glass sits only in fissures and cavities as filled natural corundum (see the disclosure requirement on this page).
The glass component may deteriorate over time and is unstable to elevated temperature and chemical agents.
What to ask for on the report
Filler and extent both belong on the paperwork: CIBJO requires the substance to be named, and glass-filled corundum is graded minor, moderate or significant on a corundum report (LMHC Information Sheet 3 covers corundum glass-filled fissures). A significant extent stays in the treated-corundum branch rather than becoming a manufactured product.
Before you buy: what to check
Work through these in order before paying. None of them replaces a laboratory report; they decide whether you need one.
- The description has to name the filling substance and disclose how much of it there is
- CIBJO requires both. US 16 CFR §23.25(d) does not allow a product made with a filler or binder such as lead glass to be called “ruby” or “treated ruby”, and calling it “composite ruby” requires a clear statement that it differs from the named stone and needs special care
- LMHC Information Sheet #3, by contrast, keeps reporting stones whose glass sits only in fissures and cavities as filled natural corundum (see the disclosure requirement on this page). The glass component may deteriorate over time and is unstable to elevated temperature and chemical agents.
Filler and extent both belong on the paperwork: CIBJO requires the substance to be named, and glass-filled corundum is graded minor, moderate or significant on a corundum report (LMHC Information Sheet 3 covers corundum glass-filled fissures). A significant extent stays in the treated-corundum branch rather than becoming a manufactured product.
Name the filler (resin, oil, polymer, glass or lead glass) and bear in mind that fillings can be unstable and may deteriorate or change colour over time.
LMHC Information Sheet #3 treats corundum with glass in two ways: glass in fissures or cavities is still reported on natural corundum as a filling, and only a badly fractured single piece infused throughout, or small fragments bound together with glass, is reported as a manufactured product.
Questions about this treatment?
Disclosure practice for this treatment differs between authorities and markets, and a report does not always say what was done.