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1. Dyeing: “a treatment that adds color or affects color by deepening it, making it more even, or changing it (GIA (2002), p. 34; Colored Stones book 6: Treatments).” It works on gems with porous surfaces like lapis lazuli, chalcedony, jadeite, coral, cultured pearls, and turquoise. If a gem has surface reaching fractures, these can include light-colored sapphires, rubies, colorless quartz, beryl, and so many others.
2. Heat: “exposing a gem to rising temperatures for the purpose of changing its appearance (GIA, et. al).” While not always predictable, the treatment is often permanent. Factors included are:
• Temperature control
• Rate of heating and cooling
• Duration of heating and cooling
• Atmosphere and pressure
• Chemical composition and properties of the gem
Gems commonly heat treated are sapphires, rubies, tanzanite, zircon, topaz, aquamarine, and amber. Tanzanite is a great example of a more marketable gem because without heating it, it is a brown color, but with it, it is a striking violet blue. 95% of sapphires have been heated to improve color and sometimes clarity.
3. Surface diffusion: “a treatment in which a gem is exposed to high temperatures and chemicals to allow color-causing elements to penetrate its surface (GIA, et. al).” Surface diffusion produces a thin layer of color at or just below the gems surface. The chemicals used depend on the gemstone’s elements that cause the color in the first place. For example blue sapphire would have titanium oxide and iron oxide added because those are the two elements that give sapphire the blue color. Common gemstones for surface diffusion are sapphire, ruby, and feldspar (examples: moonstone, sunstone, and labradorite).
4. Fracture filling: “using a filler to conceal fractures and improve the apparent clarity of a gem (GIA, et. al).” This method is used for the majority of emeralds, since they have fractures that inhibit the beauty and durability of the gem. Modern fillers include colorless oils, resins, polymers, and glass. Whatever filler is chosen, it must have a refractive index that is similar to the host gem for the light to pass through it properly. This treatment prevents most filled gems from routine cleaning and typical manufacturing processes since the filler can leak out if it gets too hot. Sometimes the filler is dyed to enhance the color of the gem. Besides emeralds, rubies are another gem that is fracture filled.
5. Irradiation: “exposing a gem to radiation to change or improve its color (GIA, et. al).” The type of radiation is either X-rays, gamma rays, or using subatomic particles like electrons or neutrons. This treatment creates a color center and isn’t very permanent since heat and light can remove the color. Common irradiated gems are topaz, light-colored tourmaline, golden beryl, green spodumene, freshwater pearls, and yellow-orange sapphire.
6. Bleaching and colorless impregnation: (bleaching) “a treatment that uses chemicals to lighten or remove color,” and (colorless impregnation) “filling of pores or other openings with melted wax, resin, polymer, or plastic to improve appearance and stability (GIA, et. al).” Many light-colored cultured pearls are bleached to remove black spots and produce uniform color. Other gems using either or both treatments are turquoise and jadeite. The impregnation technique often makes the gem more durable in addition to increased beauty.
7. Surface modification: “altering a gem’s appearance by applying backings, coatings, or coloring agents like paint (GIA, et. al).” Foil backed gems can increase brilliance, affect color, and even create phenomena. Painting the culet, girdle, or other small areas can make a light-colored gemstone appear like an entirely different gem. This type of treatment is meant to be deceptive if not disclosed by the seller. Typical gemstones that get surface modification are beryl, sapphire, ruby, quartz, jadeite, pearls, topaz, and even diamonds.
8. Sugar and Smoke: (Sugar) “soaking an opal in a hot sugar solution and then in sulfuric acid to darken it and bring out its play-of-color, and (Smoke) heating a wrapped opal until smoke or ash penetrates its surface to darken it and bring out its play-of-color (GIA, et. al).” Either technique requires the substance, whether sugar or paper, to burn down to carbon where it darkens the opal. Both are very shallow treatments which makes the new coloring likely to wear off as the stone is worn and abraded.
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