Gemstone treatments
Many gemstones are treated in some fashion, for a variety of reasons. Many are treated to enhance or change their colour or clarity. Others are fragile and have to be treated to increase their durability. There are some stones that are routinely treated in order to emulate a different kind of stone. A reputable dealer will disclose any treated gems if known, as will any reputable jeweller. Failure to disclose such details may result in civil and/or administrative actions by buyers and gem associations. This is a listing of some of the most common treatments.
Many gemstones are treated in some fashion, for a variety of reasons. Many are treated to enhance or change their colour or clarity. Others are fragile and have to be treated to increase their durability. There are some stones that are routinely treated in order to emulate a different kind of stone. A reputable dealer will disclose any treated gems if known, as will any reputable jeweller. Failure to disclose such details may result in civil and/or administrative actions by buyers and gem associations. This is a listing of some of the most common treatments.
ASBL - Assembled
DBL - Doublet
TPL - Triple
Products made of multiple layers or combinations of manufactured and/or natural materials joined together. Opal Doublets or Triplets are a great example here. An opal doublet is made by taking a slice of opal and gluing it to a backing. The backing is usually black as it enhances the colours in the opal. A triplet takes it one step further, with a thinner slice of opal attached to a black backing, then covered with a clear quartz dome. The dome both protects and slightly magnifies the opal. Doublets and triplets are much less expensive and much more durable than solid opals, and you still have that fire for which opals are prized.
B - Bleaching
The use of chemical agents to lighten or remove a gemstone's colour. A very common example is the use of hydrogen peroxide to bleach pearls. Many of the so called “chocolate” pearls are often black pearls that have been bleached.
C - Coating
Surface treatments to improve appearance, provide colour or other special effects. Some gems may be “painted” with a colouring agent such as ink or metal oxides to enhance or even change the colour. Some softer materials such as coral or pearls may be coated with a colourless resin in an effort to improve their durability. A good example of a coated gemstone is the Mystic Quartz. This stone starts as a natural clear quartz which is cut and polished, then coated with an extremely thin titanium film. This gives it a brilliant and beautiful rainbow of colours with a kaleidoscope effect. Since this coating only affects the surface of the stone, it can be scratched or worn off in time.
D - Dyeing
The introduction of colouring matter into a gemstone to give it new colour, intensify present colour or improve colour uniformity. The best example I can think of for this category is a stone called howlite. Natural howlite is white, but it is a very porous stone and it accepts colour very easily. One of the biggest fakes out there is dyed howlite being passed off as turquoise.
E - Enhanced
Some gemstones are routinely enhanced but it's difficult or impractical to prove it definitively. Many dealers will just assume that the stone has been enhanced, and will use the “E” symbol if they don't know which enhancement was done. Basically, unless the stone can be guaranteed as natural, this is the way to go. This assumption protects both the buyer and the seller. If the stone is found to be positively enhanced at a later date, no one can claim that it wasn't stated at the time of purchase. One example of a stone that is routinely enhanced, is black onyx. Most examples of natural onyx show bands of white, brown, and black. Black onyx gems are usually dyed. If the seller isn't 100% positive that it hasn't been dyed, black onyx will be marked with the “E” symbol.
F - Filling
This involves filling surface fractures or cavities with hardened resin, glass or other colourless substance. I once had a piece of rough amber which I shaped and polished by hand. Unfortunately, there was a bubble just under the surface, and I broke through. Instead of grinding the amber down and reshaping, I opted to fill the bubble with resin and continue on. It worked, you can only see the resin filling if you look closely.
G - Gamma/Electron Irradiation
R - Neutron Irradiation (regulated by the NRC)
Some gems are exposed to an artificial sours of radiation to change its colour. The colour of topaz can be radically altered with this method, so that strong blue topaz is likely a product of irradiation. Strongly coloured green, pink and red diamonds are also likely to have been subjected to this treatment. Only an experienced gem-testing lab can tell for sure if it's a natural or treated.
H - Heating
Just as it sounds, this entails heating the stone and is used to affect the colour and/or the clarity. A clouded amber submerged in hot oil will often clear, and this will frequently deepen the colour as well. Amethysts are often heated to remove the common brownish inclusions they sometimes have. In fact, heating certain types of amethyst will turn it into citrine!
IMIT - Imitation
This isn't actually a treatment, it's a substitution. This is a designation for man-made products, designed to imitate and resemble the appearance of a gemstone, but not duplicate the gems' characteristic properties. For example, coloured glass or crystal can be made to resemble rubies, sapphires and emeralds or plastic can be made to resemble pearls. They may look similar, but are obviously fake when examined.
L - Lasering
This is pretty much exclusively used for diamonds. The process includes using a laser to drill tiny holes in the diamond to access inclusions that detract from the gems' appearance. If the inclusion wasn't burned out by the laser, then it can be vaporized or bleached with chemicals.
MM - Man-made
Pretty self explanatory, these are “gemstones” that are completely fabricated products. A good example is goldstone, which comes in blue, red, brown, green and other colours. Though called a stone, it's actually a glittering type of glass that has gone through a specialized process that allow copper crystals to be formed. Another example of a man-made “gemstone” is the product know as “cherry quartz”. Some have claimed it to be a natural stone, however it is only a coloured glass.
N - Natural
This symbol is reserved for stones that have not been enhanced or treated in any way. Thankfully, there is some natural beauty left in the world, and I try to go this route whenever possible.
I - Infilling
O - Oiling/Resin Infusion
As far as I can tell, these are almost the same thing with one important exception. Both involve intentionally filling cavities or fractures that break the surface of the stone, in order to improve the appearance and durability of the stone. Infilling is done with hardened substances such as glass or plastic, and oiling is done with unhardened substances, such as oil. In the picture you can see the difference in the emerald before and after oil infusion.
S - Stabilization(Bonding)
This is the introduction of a bonding agent (usually plastic) into a porous stone. This is a very common treatment for turquoise because it is such a soft stone. The process increases the hardness of the stone which allows it to be cut or drilled more easily and with less damage.
SYN or CR - Synthetic/Created
This is a gemstone that has been created in a lab and is nearly identical to the natural version in appearance, chemical composition and optical properties. Interestingly, they often sparkle more brilliantly because they don't contain the impurities that plague their natural counterparts. Lab grown gems are becoming more popular as they are almost indistinguishable from those formed in the earth, except in price.
U - Diffusion
Using certain chemicals alongside high temperatures can produce colours in some stones and also an effect called asterism (stars). Star sapphires or star rubies are good examples though they do occur naturally as well.
W - Waxing
The surface of a gemstone is covered in wax to improve the durability and appearance. It is not a permanent treatment, but it is easy enough to reapply the wax. Jadeite, turquoise, lapis lazuli and rhodochrosite are some examples of gems that are commonly waxed.
I'm sure there are other treatments that I haven't covered, and some that may differ in definition. Again there doesn't seem to be one standard set of symbols, they differ depending on who you ask and where you look. My suggestion; when in doubt, ask. Most dealers will list the codes that they use. Another good rule of thumb when looking to buy gems; if it seems too good to be true, it probably is. Until next time, happy creating and caveat emptor!