Gemstone Treatments
Treatment refers to any process other than cutting and polishing that improves the appearance of the color or clarity, or that are used to alter the appearance (color, clarity or phenomena), durability, value, or supply of a gemstone. Today, most gems are treated to improve appearance. Treatment processes can consist of heat, irradiation, dyeing, oiling, or other processes. Detection of these treatments may be easy to nearly impossible. Treatments should always be disclosed to the consumer. The following are the most common treatments that are observed in the gem trade.
Coating
This treatment is achieved by applying a thin film to the surface of a gem partially or completely in order to modify the color, luster or brilliance. Recent coatings are designed individually for different gem species and provide more than improvement of color, i.e., such as producing strong iridescent colors or luster. Some manufacturers claim that their coating formulas can improve the surface wear resistance via nanocrystalline diamond coatings, this yet to be proven. Regardless of their longevity, any ethical practice requires full disclosure.
Most commonly coated gem materials are quartz, beryl and topaz, which display quite obvious color modifications and unnatural iridescence.
Dyeing
Dyeing refers to one of the oldest treatments recorded. The treatment involves the introduction of a coloring agent into a gemstone to give it a new color, intensify an existing color or improve color uniformity.
Clarity enhancement/Fracture filling
Clarity enhancement/Fracture filling refers to the filling of surface breaking fractures or fissures with colorless glass, resin or similar substance. This process is done to improve durability, color and transparency.
Heating
The heat treatment of gems is the most common treatment technique used on gems. Reference to heat treatment of gems is found in gemological literature dating back thousands of years. However, widespread use started in the 20th century. This treatment is usually detectable in many gems. Heat treated gems are stable and the treatment is usually permanent. The vast majority of gemstones are heated to alter their color. In ruby and sapphire the treatment is often performed to improve color and clarity.
Flux Healing
This treatment typically occurs in ruby and sapphire during the heat treatment with flux components melting into and solidifying on the surface reaching fractures of the stone. In many cases this would improve the clarity by “healing” the fractures.
Diffusion Treatment
This treatment is achieved by heating sapphire extremely high temperatures while adding certain elements such as beryllium, chromium and/or titanium to the process. Currently detection of Be-diffusion is only possible using LA-ICP-MS and LIBS which are highly advanced and expensive spectroscopy techniques. On the contrary, Ti-diffusion treatment is generally detectable using microscopy by a trained gemologist. Shallow penetration of Ti creates a thin blue colored layer which can be observed with diffused light.
Irradiation
Irradiation refers to the use of neutrons, gamma, and/or electron bombardment to alter a gemstone’s color. The irradiation stage of the process is then usually followed by a heating phase to effect the change. Blue topaz is typically produced by irradiation.
Oiling
Oiling refers to a filling of surface reaching cracks or fissures in a gem with a colorless oil or resin, wax or other substance except glass or plastic, to improve the gemstone’s appearance. The purpose is to diminish the visibly of fractures and thus improve transparency in the stone. The treatment is usually not permanent.