A variety of methods, known as treatments, are used to enhance the desirability of almost every gemstone species by altering their color, clarity, and durability. Depending on the treatment, it is sometimes difficult to recognize a treatment even for an expert gemologist.

Disclosing known treatments is legally required for selling a gemstone. Non-disclosure of a treatment could mislead the buyer to believe a particular gemstone is a higher quality and more valuable than it actually is. The influence of the treatment on price depends on how long the effects last. Some treatment effects are permanent and require no additional care while others require special care to maintain the treatment. Long lasting or permanent treatments has very little to no impact on price where as other temporary treatments that require care diminish its value. The following guide provides a brief description outlining common treatments, provides examples of gemstones seen with a specific treatment, and if the treatment is detectable by gemologist or laboratory.

Bleaching
Bleaching is the process of altering or reducing a component of or all of the color of a porous gemstone through the use of heat, light, and/or chemical. Often used with additional treatments most commonly dying and/or impregnation a form of combination treatment.
Examples: Jadeite, Pearls, Coral, Chalcedony, Tiger's Eye Quartz
Detectability: It is virtually impossible to detect Bleaching by itself, but once combined with an additional treatment such as impregnation it becomes easier to identify. Requires qualified gemological laboratory using advanced analytical techniques and magnification.

Surface Coating
Enhancing the surface of the gemstone to improving appearance by enhancing color or creating a visual special effect by applying foils, lacquer, enamel, inking, or films to the surface. Backing is one way in which a coloring agent is applied to the back surfaces of gems to alter the appearance of the gemstone. Another coating treatment is when paint is applied to all side or just a portion of the gemstones surface to alter the color.
Examples: Diamonds, Coral, Tanzanite, Topaz, Pearls, Quartz
Detectability: Easily identified by skilled gemologist, except when a colorless coating is used to improve durability.

Dying & Staining
A color treatment that is intended to intensify existing color, improves consistency, or give new color to a gemstone produced by introducing colored material into porous or fractured gemstone. In some cases, fractures are sometimes intentionally induced using heat so otherwise non-porous material can be made to accept the dye. The most commonly encountered dying is Pearls that have often been dyed enhancing their color, to improve the appearance of lower quality natural and cultured pearls.
Examples: Pearls, Chalcedony, Coral, Emerald, Ruby, Turquoise, Lapis Lazuli, Howlite, Jade, Quartz.
Detectability: Requires qualified gemologist.

Filling Fractures & Cavities
The process of filling flaws breaking the surface or cavities with a similar substance to improve appearance, durability, clarity, and in some cases to increase small amounts weight. This practice is commonly performed using colorless glass, resin, wax, or oils. The materials are usually colorless and used for filling varies solids (glass), to liquids (oils). Colored filling material could also fall into the treatment classification as dying. Rubies that have been filled with glass is a common example of this treatment. Resins and glasses can potentially be used on any durable gem with surface-reaching fractures, though it is less common than other treatments.
Examples: Commonly seen with Diamonds, Emerald, Ruby, and Sapphires. Less commonly seen with Aquamarine, Topaz, Tourmaline, Quartz, and other transparent gems.
Detectability: Requires qualified gemologist using magnification.

Heating
The exposure to high temperatures to alter the gemstone's color, clarity, or improve durability. The process can be performed in a lab or with a furnace at home and is generally undistinguishable from that of heating that occurred naturally. Flux healing takes place during heat enhancement. The treatment melts down the walls of the fractures, re-depositing the molten gemstone material, sealing the fracture closed.
Examples: Amber, Amethyst, Aquamarine, Citrine, Ruby, Sapphire, Tanzanite, Topaz, Tourmaline, Zircon
Detectability: Very difficult for a qualified gemologist or gemological lab to determine the source of the heating, be it natural or as a controlled treatment.

High Pressure High Temperature (HPHT)
Heating a diamond to high temperatures under high confining pressures to remove, or change its color.
Examples: Diamond
Detectability: Requires gemological laboratory.

Impregnation
The surface of a porous gemstone is infused with a polymer, usually wax or plastic, to give it greater durability and improve its appearance.
Examples: Turquoise, Lapis Lazuli, Jadeite, Nephrite, Amazonite, Rhodochrosite, Serpentine
Detectability: Requires qualified gemologist.

Wax, Oil, & Resin Infusion
The filling of surface-breaking fissures in porous gemstones with a colorless oil, wax, resin or other colorless substances, except glass or plastic, to improve the gemstone's appearance.
Examples: Emerald and Jadeite
Detectability: Requires qualified gemologist.

Irradiation
A gemstone is exposed to an artificial source of radiation to manipulate its color. Sometimes a heat treatment is performed afterwards to further modify the color, in a combination of treatments.
Examples: Amethyst, Beryl, Diamond, Pearls, Sapphire, Spodumene
Detectability: Difficult to identify, requires gemological laboratory.

Laser Drilling
The use of a narrow focused beam of laser light to create a channel to reach darker inclusions. Once open, chemicals are used to reduce the appearance or remove inclusions all together. This treatment is generally only seen with diamonds, primarily because they are the only ones that can withstand the high temperatures from the laser.
Examples: Diamonds
Detectability: Easily identified by gemologists and gemological laboratory.

Lattice Diffusion
The addition of certain elements into the atomic lattice of a gemstone during heat treatment, with the objective of changing or emphasizing its color.
Examples: Andesine, Ruby, Sapphire, Feldspar, Labradorite
Detectability: Extremely difficult to identify, requires qualified gemological laboratory
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