You may well have heard a lot about gemstone treatments and enhancements, but what exactly does it all mean?

May 06 2015 0 Comments Tags: buying, gemstones, information, treatments


All about the gemstones treatments!

 

Gemstones are often subject to various methods in order to improve their appearance.

Some of these treatments are widely practiced and accepted in the industry today, while others are not.

Because these gemstone treatments are not always apparent to the unpractised eye, and can even be difficult even for experts to recognise, it is necessary and legally required for anyone selling a gem to disclose if any treatment procedure carried out.

Ethical gem dealers will fully disclose gem treatments.

Gemstone treatments are a perfectly legitimate practice as long as all facts are disclosed to the buyer.

 

 

Here I am going to give a short description of the commercially available treatments for the most commonly used gem materials.

 
Heat Treatment

 

The story behind the treatment…

Centuries ago, men sitting in front of charcoal fires were the first practitioners of gems heat treatment. They would blow air through pieces of bamboo into their glowing charcoal where a few stones were placed in an attempt to coax some new colours into their stones. Today, the technology is much more sophisticated, with professionals using large computer controlled electric furnaces.

Heating is the most common treatment available.

It has been properly stated that without heat treatment the world would be without many colored gemstones. 

What is heat treatment?

It is a natural treatment and a continuation of the processes that occur in the earth when the stone was originally formed. During treatment, the stone is heated to very high temperatures (approximately 1600 Centigrade) causing inclusions, chemical elements, and other impurities to reform themselves and change the colour of the stone.

 Tanzanite  - a brownish material (as mined) and heated. The gem  changed to a blue - purplish blue color.

 

There are two main elements involved in the heat treatment:

1.    Temperature

2.    Environment (atmosphere composition and pressure)

 

The mechanism which allows the modifications is unleashed by raising of the temperature. This allows chemical exchanges at atomic levels between the gemstone and its surrounding atmosphere.

Which are the effects that can occur when a stone is heated?

1.    Colour modification: from darkening to a colour change/improvement,

2.    Clarity modification: from a structural variation to a crack. 

 

Can I detect it?

Yes! Gemmologists can examine the inner workings of the stone and study the inclusions for signs of heat treatment. If the stone has been treated, tiny inclusions such as small crystals will melt during the heat treatment process. A gemmologist can easily see this using a microscope.

 

Here are some examples of some commonly heated stones and how the treatment enhances them.

  • Amethyst – Could change the colour of pale amethysts to “yellow” that will be sold as citrine.
  • Aquamarine – removes greenish undertones / deepens the colour.
  • Topaz - produce shades of blue.
  • Tourmaline – lighten darker shades of tourmaline.

 

Special care requirements

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.

 

Oiling

What is the oiling treatment?

The vast majority of emeralds are treated to improve their clarity. When the rough emerald is mined it is thrown into a barrel of oil; when it is cut, oil is used as a lubricant on the cutter's lap. The colorless oil seeps into the fissures on the surface of the emeralds. When the fractures contain the oil they are less eye visible. To complete this process oil is pressurized into the fissures of the polished stone. 

    

 

                                       

 

        

  Before and after oiling treatment 

 

 

 

 This practice is widely accepted in the trade!

The traditional treatment for emerald is oiling with cedar oil. Cedar oil is a natural product from cedar trees and is colorless, viscous and very sticky. Cedar oil has been used for fracture-filling emerald because it has a refractive index that is similar to emerald. In order to the cedar oil to penetrate the microscopic cracks in emerald, it requires some heat and pressure to do the job. First the emeralds are cleaned, usually in an acid bath. Then the gems are placed in a heated hydraulic cylinder with pure cedar oil and locked tight. The heat liquefies the cedar oil and the pressure helps it penetrate any tiny cracks in the emerald.

After several hours the cylinder is left to cool. The stones are then removed and cleaned. The cedar oil that has penetrated the emerald returns to its thick, viscous state, making it very difficult for it to leak out without the aid of ultrasonic cleaners, excessive heat or harsh solvents.

You can classify the degree of enhanced as minor, moderate or significant, depending on how many surface-reaching fissures have been filled.

 

Is it a permanent treatment?

Traditional oiling is stable but not permanent. Eventually an oiled emerald will require re-oiling to keep it looking at its best.

 

Are coloured oils accepted?

Occasionally coloured oils are used on emeralds and rubies. The idea is to add colour while concealing fractures.

 

You want to avoid buying these because you can't judge the true colour or know how bad the fractures are!

 

This is done to deceive the buyer. Fortunately this is not common and it is unlikely you will encounter this if you buy from a reputable source.

 

Special care requirements

Avoid exposure to heat, and changes in air pressure (such as in an airline cabin), or chemicals. 

 

Irradiation

What is the irradiation treatment?

The colour of many gem materials can be altered by exposing them to various forms of radiation, such as electrons, gamma rays or neutrons. Irradiation means pounding material with subatomic particles or radiation. The resultant coloration may be shallow or extend throughout the gemstone, and in some cases it is unstable to heat and/or light.


 
 

 

 

 

Beautiful irradiated Sky Blue Topaz from Gemstones Brazil

                                

 

 

 

 

Is the irradiation bad for your health?

Although the irradiation of gemstones can leave some residual radioactivity, its duration is relatively short.

Government agencies in the USA, and other gem irradiating nations, have strict regulations for the holding and testing of irradiated gems to assure that they are not released to the public until they are safe to handle and wear.

Blue Topaz

Blue topaz is the most common example of irradiated gemstone. Virtually every blue topaz sold in the market today is the product of irradiation treatment. Irradiation of blue topaz has created shades not found in natural blue topaz; prices are very reasonable for irradiated blue topaz since there is a great deal of competition in the wholesale end of this market. If you could find an untreated blue topaz, it would sell for a price comparable to untreated Imperial Topaz.

Depending on the duration and type of irradiation, and the sort of heating process used afterward, the results vary from sky, to Swiss to London blue.

London blue is the scarcest and most expensive type because it requires neutron exposure (the most expensive process), and the longest holding times.

Can I detect it?

This form of treatment is difficult or impossible to identify in most gems. In those situations where it can be detected, more advanced techniques (such as UV-Vis-NIR or Raman photoluminescence spectrometry) are usually required. However, this treatment can be detected in some gem materials without these advanced techniques, such as in diamonds that have colors not seen in natural stones, or that display characteristic color concentrations because they have been exposed to specific sources of radiation (fast electrons, radium salts, or a cyclotron reactor). 

Special care requirements

In the beryl and spodumene gemstones, the irradiated color tends to be short lived and fades upon exposure to bright light. Otherwise, there are no special care requirements for most irradiated gem materials.

 

Dyeing

What is a dyeing treatment?

It is an introduction of a colored substance into gem materials that have either a porous structure (such as agate or turquoise) or surface-reaching fractures (such as quartz or corundum), to modify their color appearance.



 

 

 

Colorless chalcedony: sphere on the left

A slice of chalcedony - on the right - may be dyed with a variety of different colors. 

 

 

 

  

Some gems such as onyx, agate and coral are dyed to produce an even color.

The art of dying agate is believed to be an ancient one, dating back to the Romans. Agate dying was revived by the Germans early in the 19th century.

 

Can I detect it?

In most gem materials, dyeing is readily detectable with magnification, sometimes in combination with a diffused light source. Concentrations of color are often present along surface, reaching fractures or within areas of a porous structure. However, in some gem materials that are structurally porous (such as coral, jade or turquoise), dyeing may not always be detectable. 

 

Special care requirements

Not bring the gem in contact with chemicals such as acetone or alcohol, which could dissolve the dyes, or have them exposed to prolonged periods of sunlight (such as leaving it on a sunny window ledge) which could cause the dyed colors to fade.

 

Fracture Filled

Filling is used on gems with surface fractures or cavities. Different chemicals are used; oil, wax, glass, epoxy, and borax are common materials.

Can I detect it?

With close examination with magnification you may be able to spot differences in surface luster, or see a spectral effect in fractures when viewed with dark-field illumination.

Ruby

The process of fracture filling ruby with transparent lead glass is a recent innovation that began about 2004 in Chanthaburi, Thailand. Rubies of good color, primarily from Madagascar, that are disfigured by fissures or surface cracks can be "repaired" using heat treatment with lead glass.

The Asian Institute of Gemology tested fractured filled rubies for durability and found them to be more durable than a typical emerald fracture-filled with oil or resin.

 

Diffusion Treatment

Diffusion treatment consists of exposing the surface of the stone to certain chemicals combined with high heat in a furnace. Generally, only the surface color changes, so if you sliced the gem in half, the inside of the stone would be a different color, usually a paler, less valuable color. The method is used to change the color of ruby, green topaz and blue sapphire. Usually the original material is a pale or almost colorless stone that is treated to change the color of the surface.

Beware with this treatment!

The new surface color is not very deep, only about half a millimeter. If the stone is damaged or perhaps re-cut, then the original, undesirable color will be noticeable.

Some dealers even refuse to trade in these stones!

 

Impregnation and stabilization

Impregnation is the infusion of wax or paraffin into a porous material. Stabilization is the introduction of a bonding agent, usually plastic, into a porous material.

Many impregnations are often “skin deep” and due to the melting point of plastic and wax, can be susceptible to heat damage.

Impregnated pieces must be kept away from heat or the wax could melt & leak... not a pretty sight!!

Impregnation and stabilization are common for turquoise.

 

Can I detect it?

In most instances a qualified gemologist can readily identify the treatment. 


Special care requirements

Care must be taken not to subject gemstones with wax or plastic impregnations to heat, such as that encountered by a jeweler’s torch, since these will likely damage the material. 

 

Bleaching 

Bleaching is a chemical used to alter / reduce a component of, or the entire color, of a porous gem. It lightens the color and is permanent and undetectable. No price difference exists as a result.

Acid bleaching causes a breakdown in the structure of most materials, so as a stand-alone treatment, leaves materials vulnerable to breakage.

Can I detect it?

Bleaching as a one-step process is virtually impossible to detect in most cases. The second step, impregnation with polymer compounds, is easier to detect by a qualified gemological laboratory using magnification and more advanced analytical techniques.

Special care requirements

Bleached gems tend to be more brittle, and they may be much more porous and thereby more absorbent of human oils and other liquids. It is suggested that pearls be kept in a soft, dry environment to avoid surface damage.

 

Coating

Coating is a process to alter a gem’s appearance by applying a coloring agent like paint to the back surfaces of gems (a treatment known as “backing”), or paint applied as a coating to all or a portion of a gemstone’s surface with the effect of altering the color.

Mystic topaz is an example of a coated gem that was conceived by Azotic

Recent reports have indicated that tanzanite is showing up in the labs with coatings on the pavilions to improve the appearance of saturation.

Can I detect it?

Once suspected, the treatment is easy to identify by a skilled gemologist except in the situation where the coating substance is colorless, and it has been added to improve durability.

Special care requirements

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

 

Lasering


The process drills very tiny holes into a diamond to provide access to an inclusion which detracts from the beauty of the stone. The inclusion can then be, vaporized or bleached to make it less obvious if it is not burned out by the lasering. Under magnification laser holes are visible when viewed at the correct angle. A lasered diamond would be classified in the slightly imperfect or imperfect category regardless of the improvement in apparent clarity and should be priced accordingly.

Can I detect it?

Easily detectable by most gemologists and qualified gemological laboratories because of the presence of the laser drill holes.

Special care requirements

There are no special care requirements for laser-drilled diamonds.

My aim with this post is to provide quality information to consumers in order to help to clarify any doubts you may have about gemstone treatments. As a gemstone producer, if any of my gems have been treated, I always disclose it. Enhancements are commonplace these days and there is nothing wrong with it so long as the buyer is made aware. Just be sure that you know what you are buying, and do not pay more them you should. Bear in mind that the market sets the values for both natural and treated stones.



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