Gem treatments: the complete guide to what happens to gems before they reach you

Heat treatment: the accepted standard

Heat treatment is the most widely applied gem treatment, used on ruby, sapphire, aquamarine, tanzanite, zircon, citrine, and many other species. It changes trace element oxidation states and dissolves or redistributes silk (rutile needle inclusions), improving both colour and clarity in many cases.

Ruby: Heating at 1,600-1,800°C dissolves silk (which was causing haziness), improves colour saturation, and can heal minor fractures. Approximately 95%+ of commercial ruby has been heated. Unheated ruby commands a 2-10× premium over heated equivalents of the same apparent quality.

Sapphire: Heating at 1,600-1,900°C produces the same effects as in ruby. Unheated sapphire commands a 3-20× premium depending on origin (unheated Kashmir carries the most extreme premium). Beryllium diffusion (discussed below) is a separate, more controversial treatment.

Aquamarine: Heating to remove yellow component (Fe3+ to Fe2+ conversion), producing cleaner blue. Universal, accepted, undisclosed in commercial aquamarine trade.

Tanzanite: Heating removes brown iron component, producing the vivid blue-violet. Universal, accepted.

Detection: Major laboratories use LA-ICP-MS trace element analysis and microscopic examination of silk healing, rutile crystal dissolution, and other microscopic heat signatures. GIA reliably identifies heated vs unheated corundum (GIA; AGL; Gübelin; AGTA treatment codes).

Fracture filling: clarity improvement

Fracture filling involves introducing a transparent material into surface-reaching fractures to make them less visible. The filler has a refractive index close to the host gem, so the fracture becomes optically invisible. Different fillers are used for different gem species:

In emerald: Cedar oil, Canada balsam, and various synthetic resins. Minor oiling is accepted and disclosed; significant filling carries a commercial penalty. See the dedicated oiling section below.

In ruby: Lead glass filling (discussed separately as the most commercially significant and problematic fracture filling treatment).

In sapphire and other gems: Less common but documented. Glass or resin filling of surface fractures occurs in some lower-quality commercial material. GIA detects and discloses fracture filling on certificates (GIA; AGL; AGTA treatment codes).

Oiling and resin treatment in emerald

Emerald oiling is the most widespread treatment in any major gem species. Virtually all commercial emerald has been oiled at some point, because emerald's jardins (characteristic inclusions) almost always include surface-reaching fractures that accept oil. The treatment is accepted by the trade as standard for minor levels; it requires disclosure; and its extent significantly affects value.

The AGL treatment extent scale provides the most commercially useful grading:

• None: No filler detected. Rare and commands a significant premium.
• Minor: Minimal filler, consistent with normal handling. Accepted; small premium over moderate.
• Moderate: Moderate filler present. Disclosed; standard commercial. No severe penalty.
• Significant: Heavy filler constituting a meaningful portion of clarity improvement. Disclosed; meaningful commercial discount.
• Extensive: Heavy filler critical to the stone's apparent quality. Disclosed; severe commercial discount.

GIA uses "no indications of clarity enhancement" or "indications of clarity enhancement" with qualitative description. AGL's four-level scale is more commercially informative for investment-grade emerald assessment (AGL; GIA; CIBJO; Wise, 2016, pp. 50-60).

Beryllium diffusion: the invisible treatment

Beryllium diffusion is the most significant advance in sapphire treatment since standard heat treatment, discovered in commercial production around 1999-2002. In beryllium diffusion, sapphires are heated in the presence of beryllium (as chrysoberyl or other Be sources) at very high temperatures. Beryllium ions diffuse into the surface of the stone, changing the colour by modifying the absorption characteristics. The result: orange to yellow sapphires produced from stones that would otherwise be of lower value, or colour improvements in other shades.

The commercial fraud potential is severe: beryllium-diffused orange sapphires can look identical to natural padparadscha sapphires (the most valuable sapphire colour) without laboratory testing. GIA detected the treatment in 2001 and immediately published the detection methodology. LA-ICP-MS is the standard detection method: beryllium content is measured in the stone's surface and compared against natural beryllium levels; elevated beryllium at the surface confirms diffusion (GIA; Nassau, 1980; Wise, 2016).

Lead glass filling of ruby: the most problematic treatment

Lead glass filling of ruby represents the most commercially significant treatment fraud in the modern coloured stone market. The treatment involves heating highly fractured, low-quality corundum material with lead-rich glass, which flows into the fractures and fills them, producing stones with dramatically improved clarity. The glass has a refractive index similar to corundum, making filled fractures appear almost invisible in casual examination.

Gem treatment impact matrix. Heat treatment of corundum is accepted with an unheated premium. Minor oiling of emerald is accepted. Lead glass filling of ruby and polymer impregnation of jade are the most commercially problematic treatments, severe discounts and must be disclosed. Source: GIA; AGTA; AGL; CIBJO; Wise (2016).

The specific problems with lead glass-filled ruby:

Physical fragility: The lead glass has a different thermal expansion coefficient from corundum. Exposure to jeweller's torches during setting or repair causes the glass to expand at a different rate from the ruby, cracking the stone from within. Acid cleaning (common in jewellery workshops) dissolves lead glass. Ultrasonic cleaning can dislodge glass from fractures.

Commercial fraud: A stone that is 30-50% glass by volume is not a ruby in any meaningful commercial sense. The ruby material is low-quality corundum that could not be sold as a gem in its natural state. The glass filling makes it appear to be a commercial-quality ruby. The price difference between a genuine commercial ruby and a glass-filled corundum fragment can be a factor of 30.

Detection: GIA identifies lead glass filling with standard gemological equipment: the filled fractures show a blue or orange iridescence flash under fibre-optic light (a "flash effect"), surface tension differences at fracture edges, and lead detection by LA-ICP-MS. Any certified gemologist with a loupe and fibre-optic light can identify glass-filled ruby in minutes if they know what to look for (GIA; Nassau, 1980; Wise, 2016).

Polymer impregnation of jade

B jade (polymer-impregnated jadeite) was discussed in detail in the jade section. Summary: bleached porous jadeite is impregnated with a colourless polymer resin that fills the micro-fractures left by bleaching. The polymer fills the porous structure, improving transparency and surface polish. The polymer degrades over years, causing yellowing, cracking, and surface deterioration. GIA detects B jade by FTIR spectroscopy. Any jadeite purchased at A jade prices must have a current GIA or major laboratory certificate confirming A jade (natural, no polymer) status (GIA Jade Research; Wise, 2016).

Irradiation

Irradiation treatment creates or enhances colour centres in gem materials by exposing them to nuclear radiation (gamma rays, neutrons, or electrons). Commercial uses: colourless topaz irradiated to blue (the most commercially significant); some tourmaline irradiated to deepen or shift colour; some diamonds irradiated (HPHT + irradiation for colour change). For blue topaz, the irradiation is universally accepted and constitutes the standard commercial product. For coloured tourmaline, irradiation must be disclosed and may cause colour instability in some varieties. GIA and AGTA detect and disclose irradiation (AGTA treatment codes; GIA; Nassau, 1980).

Surface coatings

Surface coatings apply a thin film of a different material to the gem surface to change its apparent colour or add special effects. "Mystic topaz" is the most common commercial coating: a thin-film interference coating applied to colourless topaz produces rainbow iridescence. The coating is extremely fragile: it scratches from normal jewellery wear and cannot be repaired without stripping and recoating. Coated gems have no investment value and limited durability as jewellery. GIA identifies surface coatings under magnification (distinctive surface patterns and colour distribution inconsistent with body colour). AGTA requires disclosure of coatings (GIA; AGTA; Wise, 2016).