Gemstones, Synthetics and Treatments Explained
Natural Gemstones are found in nature and are created by natural forces.
Synthetic Gemstones are manufactured gems. Also called laboratory-grown, cultured (in the case of pearls), man-made or laboratory-created, they have mostly the same chemical, visual and physical properties as natural gemstones.
Imitation or Simulant Tuerkis Gemstones are made to imitate the colour and optical qualities of a gemstone and are usually made from glass, plastic, or less expensive stones, even though they may look like the real McCoy. Examples include Cubic Zirconia’s or glass to imitate diamonds or coloured glass to imitate ruby or other gemstones.
Gemstone treatments are used to enhance the appearance or features of a gemstone.
While it is possible to treat synthetic stones, this is not the norm. Treated gemstones are usually still natural gemstones. They have also been created by the forces of nature and the interaction by man in its formation was its enhancement. Treated gemstones should not be confused with “lab”, “man-made” or “synthetic” gemstones that have been produced by man either chemically or by another process designed to mimic the conditions found in nature to produce the product.
They include the following:
Heating: Heating is the most common form of gemstone treatments. It is only detectable in a lab setting and typically irreversible in normal conditions. The lab is able to use a microscope to see internal features in the stone which will tell that stone has been heat treated. Heat can be used to darken, lighten, improve the clarity, or change the stones colour completely.
Oiling: Oiling of emerald is universal, but not EVERY emerald is oiled, (fine untouched specimens will command massive prices). Rough emerald is thrown into a barrel of oil at the mines; oil is used as a lubricant on the cutter’s lap and the colourless oil seeps into the fissures on the surface of the emeralds. This makes the fractures less visible. Oil is finally also pushed into the fissures of the polished stone under pressure. The only way you will find an emerald that isn’t oiled is if there are no surface reaching fractures (exceedingly rare) allowing oil into the gem. Oil may be leached out and fractures by steam or ultrasonic cleaning, making inclusions more noticeable. If this happens, the stone can be re-oiled.
Impregnating/Stabilising: Often used for Turquoise or Lapis Lazuli and Jade. Stabilization introduces a bonding agent like plastic into a porous material. Impregnation is infusing paraffin or wax into a porous material. Stones that have had impregnation treatment should be kept away from heat or the wax can melt. Stabilization is a more permanent treatment.
Fracture Filling/Infilling: Included Diamonds and other gemstones can be filled with glass to make them appear to have a higher clarity than they actually have. Filler can be damaged by ultrasonic cleaning, heat, and re-tipping. It is very important to know if a Diamond you buy has received this treatment. This treatment does not repair the inclusion but does make it less visible. Depending on the percentage of glass used, these gems may also be referred to as composites.
Coating: Coating is where a lacquer or film is applied to the gemstone. This enhancement has been around for hundreds of years and is still used today. In fact, this treatment has become increasingly popular to improve the colour or change the colour of gemstones. An example of this treatment is a Mystic Topaz. Tanzanite pavilions can also be coated to improve the appearance of saturation. They have also been found on Diamonds to enhance the colour. Both of these last two are meant to deceive the buyer.
Bleaching: Bleaching is a process for organic gem materials such as ivory, coral, and for pearls and cultured pearls. It lightens the colour and is permanent and largely undetectable.
Dying: Dyeing is used on some stones such as Agate and Pearls and some others. Black Onyx is the result of dying agate. This type of dyeing is acceptable and does not impact the demand for them. Some stones however are dyed that shouldn’t be. This is done to hide poor quality increasing the perceived value of the stone. This practice is completely unacceptable in the gem trade. Some stones to watch and make sure they aren’t dyed are: Lapis, Jade, Turquoise, Coral, Ruby, Emerald, & Sapphire. The dye is not always permanent.
Diffusion: Surface: Gems are heated to a very high temperature and then infused with chemicals such as titanium to penetrate the surface of the gemstone. This treatment can create an asterism (star), improve the natural colour or change the colour completely as well as improve clarity. This process is semi-permanent as the colouring can be removed by repolishing (removing the surface layer). Lattice/Bulk: Gems are heated to a very high temperature and then infused with chemicals such as beryllium to penetrate the whole gemstone. This treatment can improve the natural colour or change the colour completely as well as improve clarity. As this process penetrates the entire gem, it cannot be removed by repolishing. It is also more difficult to detect than surface diffusion.