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10 Common Gem Treatments or Enhancements

02 Dec 2021

One of the very interesting facts about finished gemstones available in the market today is that they are often treated or enhanced to alter their colour or clarity, even beyond the processes of cutting and polishing. This is called gem treatment or enhancement. Altering the colour and clarity of a gemstone increases its value and can be permanent, long-lasting or short-lived. Sometimes treated gemstones require special care from their owner.
Today, most natural gemstones are treated or enhanced in some way or other. Because these treatments are not always apparent to buyers, it is mandatory for a seller of gems to disclose the treatment procedure the gems may have received. Organizations like American Gem Trade Association (AGTA), the International Colored Gemstone Association (ICA), and The World Jewellery Confederation (CIBJO) have even formulated specific guidelines regarding the disclosure of treatments in gem materials.
Gemstone treatment processes consist of heat treatment, irradiation, dyeing, surface coating, oiling and others. The following are the most common treatments used in the gem trade.

1. Bleaching
This treatment uses a chemical or acid to reduce or remove entirely the unwanted colour of a porous gem. Most gems like jadeite, anglesite and pearls go through the process of bleaching. Corals, chalcedony, and tiger’s eye quartz are also bleached to lighten their colour.
As bleaching causes a breakdown in the structure of most materials making them more brittle, it is followed by impregnation to improve durability and strengthen the perceived colour. Sometimes a gemstone may be bleached and then dyed, a form of “combination treatment” to enhance its look. Since a bleached gem is virtually impossible to detect with the naked eye, it may require a gemmological laboratory using magnification and other advanced analytical techniques to confirm the treatment.

2. Dyeing
Dyeing is the opposite of bleaching. It is one of the oldest treatments that utilizes a chemical agent. In this treatment, a colouring agent is used to either add a new colour, intensify an existing colour or improve colour  uniformity. Though preferred for naturally porous or fractured gems, such fractures or porosity can also be induced by heating non-porous gems. Fissures are first created in the gemstone by subjecting it to thermal shock – a process of rapid heating followed by rapid cooling - which allows it to accept the dye. The process is also called quench crackling. The most common dyed gemstones are lapis lazuli, opal, pearl, nephrite jade, chalcedony, quartz and serpentine. Gems that are naturally porous do not need to be quench crackled.
While dyeing can improve the durability of the stone, there is also a strong chance that the dye fades over time when exposed to sunlight for long periods. Some dyes also dissolve when they come in contact with solvents like alcohol or acetone, causing the gem to look faded and unappealing.

3. Coating
The painting or coating treatment involves applying a colouring agent to the surface of a gem. It is partially applied to the girdle or back surface or to the complete faceted gemstone. This treatment helps to bounce the colour around throughout the stone and modify its appearance. Some coatings also produce strong iridescent colours, brilliance and lustre. The coating treatment is also known as backing. The most commonly encountered thin film-coated gems include diamonds, tanzanite, beryl, quartz and topaz. Some pearls are also treated with a colourless hard coating to improve their durability.
In most cases, a gemmologist can identify a colour-treated stone except when the coating substance is colourless. It is best to store these coated gemstones in soft packaging and keep them in a dry environment.

4. Fracture or Cavity Filling
Fracture filling or clarity enhancement means filling any surface-breaking fractures, fissures, feathers or cracks with substances such as oil, colourless glass, wax or resin. This process improves clarity, colour, stability and transparency. It began around 2000 years earlier when emerald merchants soaked the emeralds in cedar oil to enhance their clarity. In extreme cases, it has also been used to add a slight amount of weight to a gem.
The most common fracture-filled gems are emeralds, rubies and diamonds. Other transparent gems, like quartz, aquamarine, topaz and tourmaline can also be treated by fracture or cavity filling. The treatment is usually not permanent. Changes in air pressure, proximity to heat, exposure to chemicals and a jeweller’s ultrasonic cleaner can potentially alter or remove the fillers adversely affecting the appearance of filled gems.

5. Impregnation
Impregnation is more specifically filling fractures with solid substances such as wax or plastic or lead glass. The substance is first melted and then applied to the stone. Sometimes the gemstone is partially heated or put into a vacuum to allow a more complete and flawless filling.
Plastic impregnation is often used on opaque gemstones like turquoise, lapis lazuli, jadeite, nephrite, amazonite, rhodochrosite and serpentine. However, most impregnations are “skin deep” and susceptible to heat damage.

6. Heating
The process of heating gemstones began in the 20th century. Heat treatment is used in the majority of the stones to improve clarity and colour. The American Gem Trade Association (AGTA) accepts heat treatment as a standard finishing process for many coloured gemstones. Although it is easy to detect, it is a preferred treatment in many gems as it is usually stable and permanent. Rubies, sapphires, amethysts, aquamarines, tourmalines and topaz undergo heat treatment.

7. HPHT treatment
High Pressure High Temperature treatment is used on diamonds to remove or alter their colour. It helps to reduce the brownish coloration often found in diamonds and make them colourless. In HPHT treatment some types of diamonds may be transformed from brown to yellow, orangey to yellow and yellowishgreen or to blue colours. The process is considered stable and permanent and extensively used in today’s diamond manufacturing.

8. Irradiation
Irradiation is the process that consists of applying alpha, beta or gamma rays to a gemstone. It is a permanent treatment to alter the gemstone’s colour. It is sometimes followed by heat treatment, to enhance the colour of the stone. When irradiation is followed by heat treatment it is called combination treatment. The most commonly irradiated gemstone is the blue topaz. The others include fancy coloured diamonds, sapphires and quartz. While some irradiated gems fade upon overexposure to light, most are quite stable.

9. Laser
In the laser treatment, a narrow-focused laser beam is used to make microscopic holes in a gemstone to reduce the appearance of an inclusion or dark spot within. A chemical is then forced into the channel to dissolve or alter the appearance of the inclusion. This process may be followed by vaporization or bleaching. It is exclusively used on diamonds, as they are the only gemstones strong enough to withstand the high heat from the laser. Laser holes in laser-treated diamonds are easy to detect as they are clearly visible under a microscope.

10. Diffusion
Diffusion is the penetration of certain elements into the atomic lattice or molecular structure of a gemstone. This modern treatment uses a combination of chemicals and high temperatures to change or accentuate the colour of a stone. It is mostly used in corundum, i.e. rubies and sapphires.
The above treatments are used by gem manufacturers worldwide to improve the appearance of lowergrade gemstones. Sometimes old and damaged gems are also sent for treatment to restore some of their original lustre and beauty. Not only do enhancements make such gems look much more beautiful, but they also make acquiring beautiful gemstones more affordable. While some of these processes are accepted by the trade, especially the certified ones, others may be unscrupulous attempts to pass off a lower grade stone as a fine piece. Regardless of the value a treatment brings to the gemstone, the bottom line is that ethical practice requires full disclosure.
Owning good quality gemstones may have become somewhat complicated in today’s world, but, armed with proper knowledge it is really not that difficult to become a discerning buyer and enjoy the pleasure of owning a bewitching piece of studded jewellery, or two.