Any gemstone you purchase that isn’t in its raw state has in a sense been enhanced by a jeweler. It has been cut or polished to bring out its sparkle and color.

When we talk about gemstone treatments, though, we refer to treatments which enhance color or clarity. These are additional steps which are sometimes included in the manufacturing process, but not always. Some gemstone treatments may enhance the durability of a gemstone.

Why Do Gemstone Treatments Matter?

Gemstone treatments are something you should be aware of as a buyer. However, it is not necessarily something that should be actively avoided. Unless you are only interested in natural gemstones. Treatments often reduce the value of certain gemstones, but not always.

If however you purchase a stone thinking that it is untreated, you might find yourself paying an unfairly high price for it. You might turn around to sell it later and discover its worth is much lower than you anticipated.

There is another reason it is important to be aware of the treatments used on a gemstone. Cleaning and maintenance. Gemstones which have been treated cannot always be cared for using the same methods as untreated gemstones. You may very well have to use other cleaning techniques than you normally would, or risk damaging your gemstones.

In theory, sellers have to disclose this information to you when you are shopping. The United States Federal Trade Commission has a whole set of guidelines established (source: FTC Guideline 23.22). As do similar bureaus in countries throughout the world. Professional organizations like the International Colored Gemstone Association (ICA) also have rules set in place for their members (source: ICA)

It is a good idea to familiarize yourself with the different ways that gemstones can be treated or enhanced before you decide to go shopping. That way when you read the disclosures for gemstone enhancements, you will understand what you are looking at.

There are also situations where you might not have those disclosures available, and need to know what you have. Perhaps you inherited some estate jewelry, and nobody kept good records. In order to know what you have, you need to be able to recognize treated vs. untreated gemstones or at least know what gemstones are commonly treated.

Regularly Used Gemstone Treatments

There are a number of different treatments out there which are used to enhance color or clarity of gems. Some of the most common treatments include:

• Bleaching
• Surface Coating
• Dyeing
• Fracture Filling
• Heat Treatment
• Impregnation
• Irradiation
• Laser Drilling
• Lattice Diffusion
• Oiling

Each of these techniques is used on different types of gemstones to achieve different results. Let’s take a closer look.

Bleaching

Akoya pearls are almost always bleached – Credit Mauro Cateb – CC-BY-SA-3.0

Bleaching is a process that removes color from a gemstone. It is usually done in combination with dyeing. Gemstones which are commonly bleached include jadeite jade (to remove unwanted brown coloration), pearls, coral, chalcedony, and tiger’s eye.

Some of these are only bleached to lighten their color. Pearls are almost always bleached. This makes their color more uniform and keeps them bright. This is a good example of why you should not always be searching for untreated gems!

Note that bleaching does reduce the durability of a gemstone. Bleached gems may be more fragile than untreated gems.

How can you tell if a gemstone has been bleached? Unfortunately, if bleaching was the only step in the process, you usually can’t. If however there were multiple steps in the treatment process, you may be able to spot the later steps.

What should you know about taking care of bleached gemstones? Not only are they more brittle than unbleached gems, but they also tend to be more porous. They can thus easily absorb oils and may be harder to keep clean. Keep them stored in a dry environment.

Surface Coating

Mystic topaz pendant – Mystic topaz is always coated, as it does not exist in nature – Credit to Mark Somma – CC-BY-2.0

This is a very common enhancement. A type of paint is added to all or some of the surfaces of a gemstone in order to enhance or change the color. Sometimes only the back surface of a transparent gem is coated. When this is the case, the process is also known as backing.

Commonly coated gemstones include diamonds, topaz, coral, pearls, and quartz. Topaz, and quartz are typically coated to change their color completely. Mystic topaz is an example of a coated gemstone that is not found in nature. Tanzanite is rarely enhanced through surface coating, but the process is sometimes done to deepen the natural blue color.

Sometimes surface coating is done as a measure of protection, and not to alter color. Both coral and pearls are often bleached and then coated in order to boost their durability. This is an important step after bleaching, since bleaching decreases durability, and coral and pearls are both naturally porous, fragile gemstones to begin with.

It is helpful however to know that coatings can be scratched, so you should be careful with coated gemstones. Try to isolate them when you wear or store them so they are not scratched by other objects.

How can you tell if a gemstone has been coated? Sometimes you might be able to figure it out yourself, especially if there is already a tell-tale scratch. On occasion, it may be obvious for other reasons. Mystic topaz for example is always treated as it does not exist in nature. The easiest route however is to take the gemstone to a professional gemologist. There are tests that the gemologists can use to detect surface coating.

Fracture Filling

Diamond crystal – Fractures can be filled to improve the clarity of diamonds – Credit to Rob Lavinsky, iRocks.com – CC-BY-SA-3.0

While some gemstones are heat treated to create fractures for dyes, most of the time fractures are considered imperfections and are undesirable. This is where cavity or fracture filling comes in.

Gem workers may fill fractures with a variety of materials, including glass, wax, resin, and oil. These materials can effectively conceal the fractures from view, improving clarity and general appearance.

Gemstones that have been filled may weigh more than those which haven’t, but they may also be more durable, especially when glass is used.

Many types of gemstones are fracture filled, but it tends to be precious gemstones that receive this treatment. Sapphires, rubies, emeralds and diamonds are frequently cavity filled.

You probably won’t be able to detect this treatment on your own. Usually a gemologist needs to check under magnification to identify filled cavities and fractures. It is important to know if fractures have been filled though, because some types of fillers are unstable. Exposure to chemicals, heat, light or even changes in air pressure can have an effect on the filler. This may in turn change the appearance or durability of the gemstone which has been treated.

Gems like these should be stored in cool, dark places and should not be brought on airline flights (because of the pressure changes). They should only be cleaned in lukewarm water and never exposed to harsh chemicals.

Dyeing

Pearl bracelet – white pearls are seldom dyed, but colored pearls are regularly dyed – Credit Mauro Cateb – CC-BY-SA-3.0

Gemstones which are porous or fractured can be treated through dyeing to change or enhance their colors. Sometimes dyeing is done in conjunction with other treatments such as bleaching or heat treating.

A gem may be bleached of its true color before it is dyed to achieve a uniform effect. A non-fractured gem may deliberately be fractured through heat treating to make it receptive to dye.

Many types of gemstones are dyed, including pearls, quartz, lapis lazuli, turquoise, and more. Quite often when you see a bright, unexpected color in a gemstone, you should suspect dyeing. If you have ever been to a rock shop and looked at the tumbled gemstones, odds are you have encountered a lot of cheaply dyed gems.

In the cases of more expensive gemstones with higher quality dye jobs, you may need a gemologist to help you figure out whether treatment has occurred.

What else should you know about dyed gemstones? While dye will not make a gemstone unstable, the dye itself may be unstable. Dyes are easily leached out of gemstones. Exposure to heat and light can result in fading, as can contact with solvents.

Dyed gemstones cannot always be cleaned using the same methods you would use to clean untreated gems; always avoid exposure to harsh chemicals.

Heat Treating

Tanzanite crystal – Tanzanite is almost always heat treated to improve its color – Credit to Rob Lavinsky, iRocks.com – CC-BY-SA-3.0

Heat treating is usually done to change or enhance color in a gemstone. Some gemstones are also “created” through this process. Citrine for example is generally heat-treated smoky quartz or amethyst. It has an entirely different color or appearance prior to being heat treated.

Amethysts are also sometimes heat-treated in order to change them to a green quartz called prasiolite. Prasiolite is often found under the name “green amethyst”. This is wrong as amethyst is always violet or purple.

Amber is commonly heat treated in order to darken the color and clarify the gem. Aquamarine is heat treated in order to remove a natural greenish tint which is common to the gem. This leave only the blue that is generally associated with it.

Virtually all tanzanite is heat treated to create its vivid violet-blue colors. Topaz can be heat treated to fine-tune its hue. Heat treating tourmaline can lighten it or change its color, and zircons can be heated to change them from reddish brown to blue.

Ruby and sapphire are also sometimes heat treated. Rubies that have a purplish tint to them can be heat treated to pull it out and make them appear more of a “true” red. Heat treating blue sapphire can deepen the color. Both sapphires and rubies can contain needle-like inclusions called “silk.” Heat treating can optionally remove these inclusions.

When done correctly, it can also have the opposite effect. This is sometimes desirable for star sapphires, which project their “star” effect through these inclusions. The more prominent they are, the more obvious the star effect is.

Diamonds may also be heat treated in a special process known as “high pressure, high temperature,” often abbreviated HPHT. This process can remove color from a diamond—or in some cases, add color. It is more typically done to create specific colored diamonds (like blue) than it is to remove color.

Except in really obvious cases—like citrine—it can be very hard to tell whether a gemstone has been heat treated. Even a gemologist will likely need lab equipment. So if you need to identify a heat treated stone, see a pro who knows what they are doing. Heat treated stones are usually strong, but they can be brittle. Handle them with care.

Irradiation

Blue topaz crystal – Blue topaz with such a striking blue color is always irradiated – Credit to Rob Lavinsky, iRocks.com – CC-BY-SA-3.0

This is another very common form of gemstone treatment you will encounter frequently. The gemstone is exposed to radiation in order to change its color. Often, irradiation is combined with a heat treatment in order to achieve a particular effect.

Many fancy diamonds are created through irradiation. A whole rainbow of colors can be achieved, everything from pink to orange to blue to green and even black.

Other gemstones which are frequently irradiated include corundum, topaz, quartz, beryl, and spodumene. In some cases the irradiation merely deepens the existing hue, while in other cases it transforms it.

What do you need to know about irradiation treatments? It can be pretty easy to take a guess as to when irradiation has been used. You will rarely encounter a really deep blue topaz in nature, for example. So a really vibrant blue topaz has probably been irradiated.

Fancy diamonds are often irradiated, so if you bought a colored diamond without spending a fortune, you can pretty much bet on it.

In some cases it may be harder to tell, like with a yellow diamond which may actually be naturally yellow. Other colors of diamond do occur occasionally in nature, but are pretty rare, so in most cases you can assume irradiation has taken place.

Why is it important to know this? Irradiation has a beautiful effect on a gemstone, but it is one which can easily fade in certain gemstones. If you leave out an irradiated gemstone in bright light and heat for long periods of time, the colors can fade. So you need to store these gemstones in a cool, dark place.

Impregnation

Turquoise stone – Turquoise is often impregnated to smooth the stone and improve durability – Credit to Sailko – CC-BY-3.0

This is a treatment done to some porous gemstones. It involves the use of wax, plastic or polymer. The wax or other substance being used is poured over the stone to fill the porous spots and create a smoother texture and appearance. This can also make the gemstone more durable.

You will commonly encounter impregnation on stones like turquoise, lapis lazuli, nephrite, serpentine, and amazonite. If you have handled a few of these gemstones, you know from experience that there is a certain “graininess” to their texture. This is the porous attribute.

The impregnation treatment usually does not go deep into the gemstone, so the durability improvement only applies to the outside layers of the stone. These stones may also be easily damaged by heat or chemicals, since heat and chemicals can damage the wax or plastic used in the process.

This treatment is very common and can easily be spotted by a gemologist. With practice, you can probably spot it quickly too.

Laser Drilling

Synthetic diamond – Diamond can be laser drilled to remove inclusions and improve clarity and color – Credit to Steve Jurvetson – CC-BY-2.0

While most gemstones are treated by adding material and not removing it, there are times when gems are drilled into. This is typically done when there are inclusions deep inside of diamonds that need to be removed.

The only way to reach them is with a laser drill. A chemical additive can then be pushed down the channel created by the drill to fill the inclusion (and the channel itself).

Most gemstones do not have the strength to stand up to laser drilling, which is why you will only see laser drilling used on diamonds. It is not a very common treatment, but it can be detected because laser drill holes are left behind. A gemologist can spot these drill holes with ease and let you know if your diamond has been drilled.

This is really important for you to know. Why? The holes can only be seen through a microscope and should have no impact on appearance, but the value of the diamond will be far lower. The process creates no problems as far as durability is concerned. Your diamond will be just as strong after it is laser drilled as it would have been before.

Lattice Diffusion

Cushion cut blue sapphire – sapphire can be lattice diffused to improve its color – Credit to Wiener Edelstein Zentrum – CC-BY-SA-4.0

This is a high-tech procedure which is quite challenging for a gemologist to detect. During lattice diffusion, the color of a gemstone is altered through an actual chemical change on the atomic level to the gemstone’s lattice. This process is often used on sapphires.

As you may know, simple impurities in a sapphire’s lattice account for the different colors. Chromium for example makes a sapphire red, and we call it a ruby.

Since 2003, there has been a lot of success with lattice diffusion and the element beryllium. Some other gemstones sometimes are treated this way as well, including feldspar.

While you may be discouraged at how hard it is to detect this treatment, you do not need to worry about from a durability standpoint. The treatment should have no impact on how durable your gemstones are.

You can care for a treated sapphire just as you would an untreated sapphire. Lattice diffusion is one of the reasons why you should only buy from a seller with a good reputation.

Oiling

Emerald crystal on matrix – Emerald gemstones are almost always oiled to improve its looks and durability – Credit to Gery Parent – CC-BY-SA-4.0

Oiling is an extremely common gemstone treatment, especially for emeralds, which are almost all oiled right after they are mined. The oil used is colorless and is able to seep inside the emeralds through the fissures in the surface.

The oil conceals the fractures, making them harder to detect, thus improving the looks of the emerald. Sometimes oiling may be used on stones like ruby, alexandrite, and garnet for the exact same reason.

Occasionally the oil is colored; while the main goal is to conceal the fissures, this is a sneaky way of deepening the color. This is not done very often and it is considered bad business since it can be very deceptive.

What should you know about oiling? Again, you can more or less assume almost any emerald you pick up has been oiled. The only exception would be an emerald that had no fissures on its surface, and thus the oil was unable to penetrate the stone.

A gem like this would be worth far more than any oiled emerald for the simple reason that it has no inclusions, and inclusions always impact the value of a gemstone.

Be careful when you clean emeralds and other gemstones that have been oiled. If you use a steam cleaner or ultrasonic cleaner, you may remove the oil. This will not only adversely affect the appearance of the stone, but will also weaken its durability. If this happens, you can bring it to a gemologist to be oiled again, so the damage is not permanent.

Now you are familiar with the common gemstone treatments which are used to enhance the appearance of gemstones.

There is nothing wrong with purchasing a treated gemstone, but it is important to know whether your stone has been altered or not. That way you know if you are paying a fair price for your gemstone and you can take special precautions for cleaning or storage if needed.