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Gemstone Treatment

Gemstone Enhancement Codes*

  • N = Not Enhanced
  • D = Dyeing
  • HP = Heat & Pressure
  • O = Oiling/Resin
  • SC = Speciial Care
  • CMP = Composite
  • B = Bleaching
  • F = Filling
  • I = Impregnation
  • R = Irradiation
  • W = Waxing/Oiling in Opaque Stones
  • C = Coating
  • H = Heating
  • L = Lasering
  • U = Diffusion
  • ASBL = Assembled

*Codes and type of treatments must only be used as directed in the Gemstone Information Manual, available at www.agta.org/info.

 Your sparkling gemstones are not naturally as alluring as you find them in your favorite jewelry. A drab gem undergoes number of treatments to enhance color, clarity, brightness. The treatment and improvement of gemstones has been globally recognized since years, those having permanent changes are only accepted in the trade.

American Gem Trade Association (AGTA), International Colored Gemstone Association (ICA), and The World Jewelry Confederation (CIBJO) have sketch out guidelines regarding treatment exposures and special contemplation issues.

The below information will give quick look of the common treatments, and the latest innovations. Notwithstanding improving their appearance, on the off chance some procedure might affect its durability, mostly making them more fragile. Remember that most colored gemstones are dealt with, and this is an absolutely permissible practice.Any procedure done disclosed by the gem merchant at the time of selling helps buyers to make decision.

Different Treatments


You will appreciate a rich bright color stone and want to treasure it forever. Heating is the most common treatment used to alter the saturation of color or sometimes completely change the tint of a stone. Heating cause permanent changes to the gem. These cannot be reversed under normal conditions.The enhancement is like continuing the natural process under the earth.

Unaltered stones are harder to validate, thus it is very easy to deceive an unknowledgeable buyer.Heating Amethyst adjust the hue towards lighter side into paler yellowish Citrine. The tint deepens into more bluish shade on heat treatment of Aquamarine. Similarly, the procedure removes brownish color component in Tanzanite to produce strong purplish-blue shade. More viable colors including red, blue, or colorless of zircon is produced under this enhancement method too.

Heat treatment not only dissolves inclusions, improvise color but also heals tiny cracks.The re-crystallization of mineral component in Ruby happens as exposed to heat equivalent to its melting point, results into better red hue. The stone is heated to approximately 1600 Celsius causing rutile “silk” inclusions to dissolve, which improves both clarity and color.

Microscopic rutile needles and tiny gas bubbles in unheated Rubies and Sapphires are evidence that guarantees that these stones have not been heated. Treated Ruby and Sapphire are free from these inclusions.

The commonly heat-treated gems to adjust shades also include Sapphire, Amber, Kunzite, Tourmaline and Morganite. Irradiation followed by heat treatment turns colorless topaz into shades of blue and produce a pink topaz on heating yellowish pink topaz.

Heated gemstones are slightly more brittle than usual, thus care must be taken not to scratch or break sharp faceted corners and edges.


Another common enhancement is the oiling of stones.Some gems, like emeralds are prone to fracture, thus many of times tiny internal fissures are evident. They are serious defect that diminishes the beauty and clarity of gem. These are also point to be considered in the cutting process. Oiling affects the clarity and brilliance of the gem by reflecting light off of its oiled surfaces.

Oiling an Emerald is a widely acceptable practice. The procedure begins with immersing Emerald rough into a lubricant bathe. Colorless oil smear seeps into the cracks as a result of pressure applied on the polished stone. Occasionally colored oils are used to add color while concealing fractures. This is done to deceive the buyer.

Oil masked Emerald poses serious problem to the gem cutter because it may increase the risk of damage to a great extent. If oil treated emerald that originally had fissures is put into an ultrasonic cleaner then the oil may leach out from fractures and make the surface inclusion appear whiter. In this case, the stone can be re-oiled.

Rubies, Alexandrite, Chrysoberyl, and Garnets are also oil enhanced. These oil and resin filled gems make surface inclusions less visible. Hardeners like Opticon applied after filling resins firmly seals the factures.


Irradiation method involves hammering the gem with an artificial source of radiation to change its color. Gems sometimes undergo combination treatment where irradiation is followed by a heat treatment to better or achieve a new color for the gem.

The best and commonest example is blue topaz. Natural blue topaz is rare; hence, most blue topaz available in market is irradiated. The atomic radiations impeded on colorless topaz absorb certain frequencies of light and this lead to production of different colors by modifying the crystal structure.

Irradiation of blue topaz has created shades from light sky blue, to medium Swiss blue and darker London blue. Longer neutron exposure and holding time required for London blue hue is the most expensive, making it the scarcest.

Pink Tourmaline is irradiated to darken into red. Combination treatment results into astounding mixture of colors like black, green, blue green, deep yellow, orange, pink and red Diamonds.Similarly gray color cultured Pearls are also obtained by irradiation. Varieties of Quartz are irradiated and heated to produce dramatic green quartz or Amethyst.

Beryl and Spodumene can be irradiated to deepen or change the natural color. The irradiated color in these is not stable and fades upon exposure to strong light.

Prices are very reasonable for irradiated gems.


Dyeing is yet another smart technique to hide pores or factures in gems. The process strategically involves injecting colored dyes into the factures to change color of gems, sometimes heating is required to fulfill the purpose.

The most commonly dyed gems to enhance color are Pearls, Coral, Agate or Chalcedony, Turquoise, Ruby, Emerald, Lapis Lazuli, Howlite, Nephrite Jade, Sapphire and Quartz.

Dyeing of Agate and Pearls is common and is tolerable. To meet the demand of colored pearls some cultured pearls are dyed into various overtones of colors. It is fairly easy to detect such pearls by looking for speckles around holes or surface. The porosity or minute factures hold the dye well while if the fractures are wide, the unsteady dye can leak when exposure to the ultraviolet light. Poor quality dyed lapis lazuli can easily come out when rubbed with an acetone soaked cotton ball.

The durability of dyeing depends on the stability of dye. Gemologists with the use of spectrographic analysis and several microscopic observations can easily detect dyed gems.

Impregnation and stabilization

Under impregnation the surface of gems is infused with polymer or waxed to deepen its color and durability. The practice is frequently detected in trade. Impregnation and stabilization are complimentary to each other. Stabilization is introduction of hardening agent to make the bonding more perfect.

Some gems are waxed on the surface to enhance luster but this is not very usual. It is commonly seen in turquoise, whereas uncommonly opal can also be stabilized to mask crazing. Other encountered waxed gemstones are usually opaque, and they include Lapis Lazuli, Jadeite, Nephrite, Amazonite, Rhodochrosite and Serpentine.

Due to the melting point of plastic and wax the enhancement is vulnerable to heat. As long as the impregnated gem is not exposed to heat or chemicals the wax does not come out. The experienced eyes of Gemologists can identify impregnation.


Bleaching is a process to lighten the color of gems by using some bleaching agent like hydrogen peroxide. Sometimes used as combination treatment with dyeing. In Jadeite the process involves two steps. Firstly, any unwanted brown impurities are removed by acid wash; then polymer impregnation is used to fill the pores caused. This betters appearance of the gem.


The change brought is permanent and cannot be detected. Materials such as Ivory, Coral, Jade, Pearls, Chalcedony and Tiger’s eye quartz may be bleached.

Acid bleaching makes the gem susceptible to breakage, hence, impregnation follows to improve the robustness and fortify the color.


Coating is an age-old procedure used for altering appearance of gem where a thin film of lacquer or some coloring agent is applied to the back plane of the gem, the process of “backing” or over all the surfaces to improve a gem's color.

Sparingly used to coat an off-colored Diamond, this might be used as tool to deceive buyers. The filmy coating may sometimes used to change color of Diamonds. A permanent ink marker is used to adjust the saturation to deepen the blue-violet hue of Tanzanite. The color of the ink used as coating agent along the girdle surface or pavilion of a gem affects its overall appearance. These days, coating with thin metal oxide film is more prevalent. Vapor deposition of metal oxides as thin film alters the color of Quartz crystals and Topaz.

Opal, Coral and Pearl are also coated both to intensify their tone and improve the durability.

Protect thin-film surface coatings of gem from any kind of scratches. The coating is very delicate along surfaces, especially ends and joints. Do not let any harsh object nick it.


Diffusion entered the list of gemstones when in 1980 sapphire was diffused with titanium and chromium. Diffusion is described as the penetration of certain elements into the atomic structure with the sole purpose of altering or enhancing its color.

In 2003, Corundum Sapphire was again diffused with a new chemical beryllium at high temperatures, and actually penetrated the gem to change color or creates asterism (stars). Feldspar like Andesine and Labradorite, Ruby, Tourmaline and Tsavorite (the green garnet) can claimed to be diffused.

It is a controversial treatment that one should be aware of. When the surface of a stone is exposed to heat combined with certain chemicals coloration is produced on surface only, few millimeters deep. Hence, this process of diffusion is also called "Surface Diffusion". The problem is if you slice the gem the core of the gem is paler, which is of lesser value. Be careful of this treatment as damage or re-cutting a diffused stone may reveal the undesirable color.

The diffusion would penetrate deep into the entire stone if the gemstone is heated to very high temperatures for long hours.

The changes are permanentand the treatment is only detected by laboratory testing.


Facture filling is another practice that is prominently used by sellers to deceive buyers.

The external fractures or cavities are filled with glass, resin, wax or oil like substances to hide their visibility and to improve the clarity of gem. Filling materials somewhat provides stability and add also add mass to a gem. The fillers are colorless or colored dyes. This treatment is often visible under magnified lens. The difference in luster and spectral effect reveals the facture filling done to it.

Diamonds with inclusions are sometimes filled with high lead content glass to lessen facture visibility and make them appear clearer. The filling only makes the inclusions less visible.

If you are going to buy a Diamond have a closer look at it under light for any facture. The filled facture can be noticeable by a bluish flash. Ruby and Emerald are the other gems which undergo fracture filling treatment. There appears major difference in light reflected off their surfaces, before and after the treatment. The tiny cavities once again become transparent.

Though less, facture filling for Quartz, Aquamarine, Topaz, Tourmaline and some other transparent gems is also prevalent.Filled gem when subjected to any change in air pressure or exposure to heat, or contact with chemicals causes undesirable damage to them. Ultrasonic cleaning and re-tipping may remove the filler substance and potentially alter the appearance, so avoid them.


Sometimes laser or drilling treatment is encountered in Diamond trade. This procedure includes burning an open channel from the surface of a Diamond by focusing a narrow beam of laser to force a chemical for dissolving dark inclusions. Huge heat is generated in lasering and only Diamonds can withstand this heat. Laser treatment is exclusively used to modify Diamonds. Under magnification the holes imprinted by laser can be clearly seen. Laser treated Diamond is categorized as “slightly imperfect” or “imperfect”.