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Gemstone Enhancements: Heat Treatment, Irradiation, etc.





Various Gemstone Enhancements


Gem Enhancement Awareness

It is important for the consumer to be aware of the fact that many varieties of gemstones on the market today have been treated or "enhanced" in order to improve their appearance. Additionally, there is a constant battle between unscrupulous gem traders and testing laboratories to hide and detect new treatments.



Consumers should always require disclosure of any alterations or enhancements of a gemstone before making a purchase. This is especially important if the enhancement to the treated stone is not permanent or if the treated stone will require special care.

The Federal Trade Commission publishes FTC guidelines for the jewelry trade, stating that consumers must be informed of any gemstone treatments that are not permanent OR that "significantly affects" the value. Most comprehensive gemological reports identify treatment types, and when purchasing a large, expensive stone it is advisable to have a full GIA or AGS report done.


Gem Enhancement Classifications

The designation for identifying enhancements on a gemological report is: "N" (not enhanced), "E" (normally enhanced), and "T" (nontraditional enhancements). Commonly used methods of enhancement are:


Semi-Permanent or Temporary Gem Enhancements

  • Bleaching (B): Used to lighten and/or whiten gemstones or pearls
  • Coating (C): Surface enameling, inking, foiling, lacquering, sputtering, or vapor deposition
  • Dyeing (D): Used to enhance the color and uniformity of gemstones or pearls
  • Filling (F): Filling surface cavities or fissures with colorless glass, plastic or resin
  • Impregnation (I): Treating gems with oil, wax, or resin to improve clarity & appearance
  • Waxing (W): Impregnation with colorless wax, paraffin or oil

Permanent Gem Enhancements

  • Flux Healing (FH): Heat enhancement used to heal fissures and fractures
  • Fracture Filling (F): Injecting plastics or glass into fractures
  • Heat Treatment (H): Used to lighten, darken, or alter color
  • Irradiation (R): Used to add color intensity to diamonds, gemstones, or pearls
  • Lattice Diffusion (U): High-temperature heat treatment to produce color and/or asterism
  • Lasering (L): Laser and chemical treatment to remove inclusions

Most of the 'temporary' enhancements or treatments are basic and self-explanatory, but most of the 'permanent' gem enhancements involve highly sophisticated techniques that can be difficult to detect. Most treatments leave some kind of telltale signature or fingerprint, but as treatment methods become increasingly subtle, they are more problematic. Some of the more involved treatments and enhancements are listed below. These treatments are permanent, but can have a significant impact on the value of a gem.


Flux Healing

Flux healing involves the filling of surface cracks, cavities, and/or inclusions by exposing the crystal to a combination of heat and borax or other fluxes and solvents to fill voids with molten low-viscosity flux glass. As the flux mixture fills a fracture via capillary action, the molten mixture dissolves the walls of the fracture until the liquid in the crack becomes saturated with the actual mineral's molten solution.


Heat Treatment

Heat treatment or 'annealing' is done using a combination of chemicals (beryllium, borax, lead, tantalum) and heat to permanently alter a stone's color. Heating or "cooking" the stone is done at temperatures ranging from 450 to 1850 Celsius for a period of 2 to 12 hours or more. One telltale sign of heat-treatment is the presence of small fractures or "decrepitation feather" within the stone that appear around natural mineral inclusions.


High-Temperature High-Pressure (HTHP)

High-Temperature (2,000 C) High-Pressure (70,000 atmospheres) treatment or HTHP was developed by General Electric in 1999, to lighten or totally remove a brownish hue in some Type IIa diamonds. Type I diamonds have nitrogen impurities that absorbing some of the blue light spectrum, thereby making the diamond appear yellow, while Type II diamonds have structural defects (aka plastic deformations) created during crystal growth, that can cause a brownish color. High-Temperature High-Pressure treatment can in some cases 'repair' these deformations, whitening the diamond's appearance.



Type I diamonds which have nitrogen impurities can also have their color altered using High-Temperature High-Pressure treatment. Using HTHP, a company called Nova Diamond creates fancy colors in vivid hues of yellow and green, bypassing the need for irradiation.

Diamonds treated by General Electric (Pegasus Overseas Ltd) to remove coloration have the logo "GE POL" laser-inscribed on the girdle, but laser-inscriptions can be removed by polishing. Detection of non-inscribed HTHP treated diamonds is accomplished by gemological testing laboratories using photoluminescence spectroscopy, 'Fourier Transform Spectroscopy' (FTIR) and 'Raman Spectroscopy' to analyze visible and infrared light absorption looking for telltale absorption lines that would indicate high temperature exposure. Additionally, telltale fingerprints that can be seen under a microscope may include dark cracks around inclusions, internal graining, haze, and partially healed feathers.


Irradiation

Irradiation treatments involve exposing the stone to electromagnetic rays (ionizing radiation) or gamma rays (cobalt 60 radiation) to release electrons from their normal location, moving them to more desirable color-producing locations. Depending on the mineral to be treated, and the desired color alteration, alpha particles, beta particles, electrons, gamma particles, neutrons will be used in the irradiation process. Irradiation treatment uses a linear accelerator to expose the stone to high-energy electrons, a cyclotron for charged high-energy particles such as protons, or an electron-beam nuclear reactor to expose the stone to high energy neutrons. Neutron bombardment and electron bombardment are the two main irradiation methods practiced today.

Residual radioactivity in the stone can be a potential concern. The use of a nuclear reactor can create radioactive isotopes in the stone, necessitating storage for a sufficient amount of time for the decay of any residual radioactivity.


Lasering & Laser Drilling

The laser-drilling of diamonds to reduce or remove foreign crystal inclusions, or iron-oxide stained fractures, has been preformed for over 20 years. Drilling is accomplished using an infrared laser to bore microscopic holes (0.005" diameter) into a diamond, creating an access channel to the inclusion. The diamond is then immersed into a sulfuric acid solution to dissolve any non-diamond crystals and/or staining. The laser-drilling process is followed by glass in-filling to hide the channel, using a glass material with a refractive index that approximates diamond. Several inclusions can be removed from the same diamond using this technique.

Visible signs of laser-drilling and subsequent glass-filling can easily be detected under a microscope, and may include semi-opaque white lines that are straight or slightly wavy in appearance, air bubbles and/or flow-lines within the glass-filled hole, and dark circles where the holes breach the diamond's surface.


Lattice Diffusion

Lattice diffusion is a treatment process using a combination heat and chemicals to 'diffuse' or deposit an element (beryllium, chromium, vanadium, etc.) from an external source into a gemstone in order to alter or improve its color hue or saturation. This treatment is used primarily on corundum (rubies and sapphires) and is considered an unethical practice. Diffusion is a mechanical process where atoms and/or ions move through solid matter. Within a crystal's lattice structure there are missing atoms called "vacancies" that can be filled with a new element's atoms, thereby changing the chemical composition and color of the mineral.

Lattice diffusion can be difficult to detect, and therefor, is considered an unethical practice. The diffusion treatment of ruby and sapphire in-particular is major concern within the gem trade.






Gemstones & Their Treatment Types

Most gemstones, with the notable exception of garnet, have a particular treatment, or series of treatments that are commonly used to increase the marketability of the stone. This list represents common gemstones and the typical treatments they receive.


Conclusion

There is nothing intrinsically wrong with gem enhancements as long as you are made aware of their use. New treatments are being developed all the time, and gemological testing centers are constantly revising and updating their testing regimes to combat the unidentified enhancement that can slip through the cracks. As consumers, we must rely on the testing laboratory's ability to identify enhancements so that a gem's value can be properly ascertained before a purchase is made.


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