Gemstone Care by Treatment: Oiled vs Heated Gems

Gemstone Care by Treatment: Oiled vs Heated Gems

The majority of gemstones sold today have been treated in some way to enhance their color or clarity. Heat treatment, oiling, fracture filling, irradiation, and coating are among the most common treatments. Each treatment affects how a gem should be cared for, and using the wrong cleaning method on a treated gem can cause serious and irreversible damage. Understanding your gem's treatment status is essential for proper care.

Why Treatments Affect Care

Treatments work by introducing foreign materials into the gem (oils, resins, glass), altering the gem's crystal structure (heat, irradiation), or applying surface coatings. These modifications can be sensitive to heat, chemicals, ultrasonic vibration, and prolonged water exposure in ways that the untreated gem is not. A cleaning method that is perfectly safe for an untreated sapphire may dissolve the filler in a fracture-filled ruby or remove the oil from an emerald.

Heat Treatment

Heat treatment is the most common gem treatment and is applied to the majority of sapphires, rubies, aquamarines, tanzanites, and many other gems. Heat treatment alters the color of a gem by changing the oxidation state of trace elements or dissolving inclusions. Once heat treatment is complete, the gem's crystal structure is stable and the treatment is permanent.

Care implications: Heat-treated gems (without any filler) can generally be cared for the same way as untreated gems of the same species. Warm soapy water, soft brush cleaning, and ultrasonic cleaners are all appropriate for heat-treated sapphire and ruby without fracture filling. The treatment itself does not create any special care requirements.

Oiling

Oiling is the most common treatment for emerald. Cedar oil, synthetic resins, or other substances are introduced into surface-reaching fractures to improve clarity by reducing the visibility of fractures. The oil has a similar refractive index to emerald, making fractures less visible. Most emeralds on the market are oiled to some degree.

Care implications: Oil can be removed by ultrasonic cleaners, steam cleaners, prolonged soaking in water, and some chemical cleaners. Removing the oil makes fractures more visible and reduces the gem's apparent clarity. Clean oiled emeralds only with a soft damp cloth. Never use ultrasonic cleaners, steam, or soaking. Avoid prolonged exposure to hot water. If an emerald loses its oil over time, it can be re-oiled by a professional gem treater.

Fracture Filling

Fracture filling uses glass, resin, or other materials to fill surface-reaching fractures in gems, improving apparent clarity. It is used in emerald (similar to oiling but with more viscous materials), ruby (glass filling is very common in lower-quality rubies), and occasionally other gems.

Care implications: Fracture fillers are sensitive to heat, ultrasonic vibration, and chemicals. Ultrasonic cleaners can shatter glass fillers. Steam cleaners can melt or displace fillers. Acids and some cleaning chemicals can dissolve fillers. Clean fracture-filled gems only with a soft damp cloth or very gentle warm water cleaning. Never use ultrasonic cleaners, steam, or chemical cleaners. Avoid prolonged soaking.

Glass-filled ruby requires particularly careful handling. The glass filler can be damaged by even mild cleaning methods if applied aggressively. Wipe gently with a soft damp cloth and avoid any chemical exposure.

Irradiation

Irradiation uses gamma rays, electron beams, or neutron bombardment to alter gem color. Blue topaz (almost all blue topaz on the market is irradiated), some diamonds, some tourmalines, and some other gems are irradiated. Irradiation creates color centers in the crystal structure.

Care implications: Irradiated gems are generally stable under normal conditions. The color is permanent in most cases. However, some irradiated gems are also heat-treated after irradiation to stabilize the color, and these should be kept away from high heat. Standard cleaning with warm soapy water is appropriate for most irradiated gems. Avoid prolonged exposure to strong UV light for some irradiated gems, as UV can affect color centers over very long periods.

Surface Coating

Some gems are coated with thin films to alter their color or add optical effects. Mystic topaz and some other gems have metallic coatings applied to their pavilion (bottom) to create rainbow color effects. Some diamonds are coated to alter their color.

Care implications: Coatings are the most fragile of all gem treatments. They can be scratched, chipped, or dissolved by cleaning chemicals. Clean coated gems only with a soft damp cloth. Never use ultrasonic cleaners, steam, abrasive cleaners, or chemical cleaners. Avoid contact with other gems that could scratch the coating. The coating can be damaged by normal wear over time and cannot always be restored.

Beryllium Diffusion

Beryllium diffusion treatment heats corundum in the presence of beryllium, causing beryllium atoms to diffuse into the surface layer and alter the color. It is used to produce orange and padparadscha-colored sapphires and some rubies.

Care implications: Beryllium diffusion is a stable treatment once complete. Care requirements are the same as for heat-treated corundum. The treatment is permanent and not affected by normal cleaning methods.

Waxing and Impregnation

Turquoise and some other porous gems are commonly waxed or impregnated with resin to improve color stability and durability. The wax or resin fills the pores of the gem.

Care implications: Wax and resin impregnation can be damaged by heat, solvents, and ultrasonic cleaners. Clean waxed or impregnated gems only with a soft damp cloth. Avoid all chemical cleaners, ultrasonic cleaners, and heat exposure.

How to Find Out If Your Gem Is Treated

  • Ask your jeweler at the time of purchase. Reputable sellers disclose treatments.
  • Check the gem certificate if one was provided. Major lab certificates from GIA, AGL, and Gubelin disclose treatments.
  • Have the gem tested by a gemological laboratory if you are unsure.
  • Assume emeralds are oiled unless certified otherwise. Assume most blue topaz is irradiated. Assume most commercial ruby has some degree of treatment.

Frequently Asked Questions

Does treatment reduce gem value?

It depends on the treatment and the gem. Heat treatment in sapphire and ruby is so universal that it has minimal effect on value for most commercial stones. Fracture filling significantly reduces value. Oiling in emerald is accepted and expected; heavy filling reduces value. Coatings generally reduce value. Untreated gems of fine quality command significant premiums.

Can treatments be removed?

Some treatments can be removed or reversed. Oil can be removed from emerald (and re-applied). Some coatings can be removed. Heat treatment and irradiation are permanent and cannot be reversed. Fracture filling can sometimes be removed but the underlying fractures remain.

Is it safe to have a treated gem resized?

Resizing requires heat from a jeweler's torch, which can damage heat-sensitive treatments. Always inform your jeweler of any known treatments before resizing. A skilled jeweler will take precautions to protect the gem, such as removing it from the setting before applying heat.

Conclusion

Treatment status is one of the most important factors in gemstone care. Heat-treated gems generally require no special care beyond their untreated counterparts. Oiled and fracture-filled gems require gentle cleaning without ultrasonic cleaners or chemicals. Coated gems require the most careful handling of all. Knowing your gem's treatment status allows you to choose the right care method and protect your investment for the long term.

Explore our complete Gemstone Care series for detailed guides on caring for every type of gem.

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