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Gemstone Treatments

Green Turquoise and Sterling Silver Ring

When I first began setting gemstones, I was dismayed to be told that one that I had chosen might have been dyed. I felt a bit cheated. Surely every gemstone was just rock that came out of the earth? I did some research, and soon found that just about every precious gemstone you see has been treated in some way, and that some of the methods have been utilised for millenia – one of the first records of treating gemstones was written by Pliny the Elder (23-79AD), and methods he outlined are still in use today.

In truth, we alter almost every gem that comes from the earth, at least by cutting and polishing it. We also treat gems in ways that can change the colour or clarity of the stone. There are some gemstones that would not even exist if it were not for treatments. Not only are these treatments acceptable, they are necessary to keep these products affordable and available. There are varying degrees of enhancements – some are permanent and cannot be detected; others are obvious; and some are less stable and may diminish durability – these should be avoided if possible.

Drusy Agate Ring Rainbow

While the gemstones I use in my work are semi-precious, and therefore should not be price-affected by treatment (and have usually not to my knowledge been treated) some of them have been (including the majority of the drusy agates I use, which have been quite obviously dyed). If any treatment is not obvious but has been disclosed to me or is apparent to me when I buy the stones, I will note that in my listing for the stone or piece.


Treatments - Bleaching

Bleached Coral (photo credit Tomomarusan)

Bleaching is a chemical process used to lighten either a component of or the entire color of a porous gem. Some gemstones are bleached and then dyed. Bleaching is permanent and undetectable. Bleaching is usually followed by polymer impregnation, as the process leaves materials vulnerable to breakage.

Gems that are commonly bleached include jadeite and pearls; some coral, ivory, and chalcedony may also be bleached.

Bleached gems tend to be more brittle, and they may be more porous and thereby absorbent of human oils and other liquids. Pearls should be kept in a soft, dry environment to avoid surface damage.

Bleaching is virtually impossible to detect in most cases.


Firey Orange Oval Drusy Agate Cabochon

Obviously dyed drusy agate

Dyeing is the practice of introducing colored dyes into porous or fractured gems to change their color. Fractures are sometimes purposely induced by heating the gem so that an otherwise non-porous material can more readily accept the dye.

Some dyeing, i.e. of chalcedony and of pearls is prevalent, permanent, and acceptable – it is not deceitful as these colors do not occur in nature. Dyeing of other materials i.e. of jade, lapis lazuli, turquoise, coral, rubies, emeralds and sapphire may be less acceptable – dyeing of these materials is usually performed to disguise inferior quality stones.

Gems that are commonly dyed include pearls, chalcedony, lapis lazuli, black onyx, pearls, jade, coral, and howlite – howlite is often dyed and passed off as turquoise. The process has also been used since ancient times for materials such as turquoise, quartz, emerald, and ruby. Agate is also commonly dyed – most of the drusy cabochons I work with have been obviously dyed – these colors don’t occur in nature! Sliced agate is often dyed as well.

When dye is applied to porous materials, the durability is dependent on the stability of the dye. In gems with larger fractures, the dye can sometimes leak out. Many dyes can be removed if the gem comes into contact with a solvent such as alcohol or acetone. Some dyes are unstable with exposure to sunlight and can fade over time.

A qualified gemologist can detect dyed gems in most cases.

Fracture or Cavity Filling, Including Oiling

Emeralds are commonly oiled (photo credit Mauro Cateb)

Emeralds are commonly oiled (photo credit Mauro Cateb)

Fracture filling and oiling are the practice of filling surface-reaching fractures or cavities with glass, resin, wax or oil to conceal their visibility and to improve the apparent clarity, appearance, or stability of gem materials. The filling materials vary from being solids (glass) to liquids (oils), and in most cases, they are colorless. The use of synthetic resins with hardeners often applied to make the process more permanent, in particular, is not considered an acceptable treatment. Filling does not repair the inclusion, it just makes it less visible.

Gems that are commonly fracture-filled include: amber, diamond, ruby, emerald; alexandrite, varieties of chrysoberyl, and demantoid garnets; quartz, aquamarine, topaz, tourmaline and other transparent gems.

Glass filling tend to be harder and therefore more durable than resins, oils or waxes.

In most cases, filled gems can be recognized by a qualified gemologist using magnification.

Avoid exposure of these gems to heat, ultrasonic cleaning, and changes in air pressure or chemicals. Filled emeralds can also be damaged by exposure to hot water used for washing dishes.

Heat Treatment

Tanzanite is often heat treated (photo credit Wiener Edelstein Zentrum)

Tanzanite is often heat treated (photo credit Wiener Edelstein Zentrum)

Heating is the exposure of gems to high temperatures for the purpose of altering their color and/or their clarity and brightness. It can cause a stone to lighten, darken, or change colour completely. Unheated stones can come with a 50%-100% price increase – this doesn’t mean that the untreated gem is more beautiful, as in most cases the heating enhances the gemstone; the higher price is because of the rarity of the stone being unheated. It is usually irreversible.

The most commonly heat-treated gems include amethyst, apatite, aquamarine, citrine (naturally occurring citrine is very rare – almost all citrine in the market is heated amethyst); diamond (diamonds can be subject to ‘high pressure high temperature’ treatments, as this can alter the atomic structure of some types of diamonds; the treatment involves heating the diamond to high temperatures under high confining pressures to remove or change its color); ruby, sapphire, tanzanite (tanzanite is often a brown colour when mined – most of the shades of violet and blue available are heat treated); topaz, tourmaline and zircon.

Heat treatments in all of the gemstones mentioned above are considered durable and permanent under normal handling conditions.

Heating is detectable only by trained observers in a laboratory setting. Unheated rubies and sapphires will contain microscopic rutile needles or tiny gas bubbles in pockets of liquid which are evidence that these stones have not been heated.

Submitting gemstones to intense heat may render them slightly more brittle than usual, and care must be taken not to damage pointed faceted corners and edges.

Impregnation and stabilization

Treatment - Impregnation

Turquoise is often impregnated (photo credit Parent Géry)

Impregnation is the process whereby the surface of a porous gemstone is permeated with a polymer, wax or plastic to give it greater durability and improve its appearance. Stabilization is the introduction of a bonding agent, usually plastic, into a porous material. Of the two processes, stabilization is the most permanent. The upside to stabilization is that treated gems will not absorb oils and discolor as much as untreated ones. Some gems are waxed on the surface to enhance luster but this is not very usual. Opal can be stabilized with plastic to hide crazing, but this is not common and would only be done deceptively.

Most commonly encountered wax or plastic impregnated gemstones are opaque. The most commonly encountered dyed gems include turquoise, lapis lazuli, jadeite, nephrite, amazonite, rhodochrosite and serpentine.

Impregnations are often only surface deep, and due to the melting point of plastic and wax, can be susceptible to heat damage. Plastic impregnations are considered durable in gem materials such as turquoise as long as they are not subjected to heat or chemicals.

In most instances a qualified gemologist can identify this treatment.


Irradiated Topaz (photo credit Rob Lavinsky)

Irradiated Topaz (photo credit Rob Lavinsky)

Irradiation is the exposure of a gem to an artificial source of radiation to change its color. (This is sometimes followed by a heat treatment to further modify the color).

Most irradiated gems will not contain any harmful residual radiation. There are some interesting articles about irradiation safety here. According to a scientist’s report I read, the only areas of potential danger are gemstones which have been irradiated by a neutron beam (which takes place inside a nuclear reactor), and given the short half life of the materials in gemstones, they should be harmless within a week of this treatment.

The most commonly irradiated gems include diamonds, corundum (includes ruby and sapphire), topaz, pearls, quartz, some varieties of beryl and spodumene.

The colour of some irradiated gems fades upon exposure to strong light. Blue topaz, diamond and quartz tend to have very stable colors as long as they are not exposed to high temperatures.

Because strong blue colors do not occur naturally in topaz, strong blue topaz stones can be considered to have received irradiation treatment. Strong colors in green, pink, and red diamonds should also be considered suspect. Determination of whether a colored diamond is natural color or treated color requires examination by an experienced gem-testing laboratory.

Laser Drilling

Diamonds are the only gemstone that are laser drilled (photo credit Rob Lavinsky)

Diamonds are the only gemstone that are laser drilled (photo credit Rob Lavinsky)

This technique involves using a focused laser beam of light to burn an open channel from the surface of a diamond to reach dark inclusions in the stone. This is generally followed by vaporizing or bleaching to dissolve or alter the appearance of the inclusion. Diamonds are the only gemstones that can be treated in this fashion, in part because only they can withstand the heat of a laser.

While lasers could potentially affect the structure of a diamond, most laser drill holes are microscopic, and have no effect on the durability of the diamond.

Easily detectable by most gemologists and qualified gemological laboratories because of the presence of the laser drill holes. There are no special care requirements for laser-drilled diamonds.

Lattice Diffusion

Sapphires can be subject to Lattice Diffusion (photo credit Sapphiredge)

Sapphires can be subject to Lattice Diffusion (photo credit Sapphiredge)

Lattice diffusion is the penetration of certain elements into the atomic lattice of a gemstone during heat treatment, with the objective of changing or accentuating its color. Diffusion was originally used on sapphires. Chemicals, like beryllium, were infused at high temperatures, and actually penetrated the gems. Early diffusion only produced color on the surface of the gem’s surface and was referred to as surface diffusion. Great advancements have been made in diffusion treatment and it was discovered that if corundum is heated to very high temperatures for a long duration, the diffusion would penetrate the entire stone. It can improve color, change color, or create asterism (stars).

The most commonly encountered diffused gems include: Corundum (ruby and sapphire), diamonds (if you look at a filled diamond closely and rotate it under light, you should be able to notice a bluish flash); feldspar (varieties of feldspar, notably andesine and labradorite are receptive to the diffusion of copper, completely altering their color); possibly tourmaline and tsavorite garnet.

The treatment is considered permanent. It is extremely difficult even for qualified laboratories to detect with certainty. There are no special care requirements for diffusion treated corundum or feldspar.

 Surface Coating

Olive Titanium Coated Drusy Agate Cabochon

Titanium Coated Drusy

Coating, a process which has been in use for over two hundred years, alters a gem’s appearance by applying a coloring agent (like paint, lacquer, or thin film) to the surfaces of gems.

The most commonly encountered coated gems include: diamonds, tanzanite, topaz, coral, pearls, quartz  (some of the drusy cabochons I use have been coated with titanium); and opals.

Because they tend to be softer than or may not adhere well to the underlying gem, thin-film surface coatings of any kind are susceptible to scratching, particularly along facet edges and junctions. Care should be taken to not allow any hard or abrasive objects to come in contact with coated gems.

The treatment is easy to identify by a skilled gemologist except where the coating substance is colorless and it has been added to improve durability.

When they are not being worn, coated gem materials should be wrapped in soft packaging and kept in a dry environment.

Gemstones That Are Not Enhanced

Malachite Cabochon

Malachite is not known to be enhanced

There are some gemstones that are not known to be enhanced. These include:

garnet (with the exception of demantoid)
varieties of chrysoberyl
tourmaline (with the exception of the Paraiba variety)
feldspar (with the probable exception of varieties of andesine and labradorite).

Bear in mind that new technology in gemstone treatment is always changing and improving and many techniques are difficult, if not impossible, to detect.


Here in Australia, the ACCC states that consumers should be able to “have a reasonable expectation that any treatment of gemstones to enhance their aesthetic appearance and value would be disclosed where the treatment is either not permanent or creates special care requirements, such as through the application of colourless oils, or the previous
practice of fracture filling. Additionally, businesses which fail to disclose gemstone treatments, where the value of treated gemstones is significantly less than the value of an equivalent untreated gemstone, may also risk contravening the misleading and deceptive conduct provisions of the Act.”

A gemstone vendor should always disclose any known treatments or enhancements; however, remember they may not always know themselves, especially with imported gems. Most gemstone vendors are honest and will let you know, but it is your responsibility to ask.

All in all, one of the reasons I enjoy working with semi-precious rather than precious stones is that they are less ‘valuable’ in monetary terms, and more likely to have come out of the ground the way they are – conversely though, to my mind, as long as the stone is obviously enhanced and you’re not being fooled into paying more for it, why not have fun and enjoy it! So, tell me – what do you think about treated gemstones?