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	Updated 30 May 2008
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This page is not intended to be a comprehensive discussion of the enhancement of gemstones, a topic which requires volumes.  Rather, we plan to present an overview of some of the more common treatments as an example of what you, the gemstone and jewelry purchaser, can expect to encounter.  This page is not a substitute for full disclosure; it is intended only as a general guide and public service.  Also, we will not discuss the details of how to actually do enhancements - that is not our business, and it is not a service we provide.

Many gemstones are treated in some way (in addition to cutting and polishing) before they are placed on the market.  In some cases, a type of stone has been treated in some particular way for decades, or even centuries.  In the gemstone and jewelry industries, these cases are considered normal and acceptable practice, and are rarely disclosed.  In some cases, disclosure may not even be required by governmental authorities.  It is our practice, though, to disclose even these treatments.  If we cannot prove the existence of a treatment, we will tell you that we suspect it has occurred, because it is probable considering the type of gemstone.

It is important to take note of the fact that ANY colored gemstone will fade if exposed to strong light (natural or artificial) for a long-enough period of time.  This time will depend on the type of gemstone, the nature of the light source, etc.  Also, many chemicals can damage gemstones; gemstones should never be exposed to extremes of heat or cold, or harsh chemicals -- including most household cleaning products.

DOUBLETS and TRIPLETS
One of the oldest "treatments" in the gemstone industry is to glue a small piece of gem material to a piece of quartz or glass to make a larger, more durable, and/or more attractive stone. These are also called "assembled stones", of which there are many varieties. This has probably been applied to virtually every type of gemstone. In some cases, such as opal, a colorless quartz top is glued to a flat piece of gemstone to provide a durable and attractive surface. This is a basic doublet. Sometimes, a thin slice of colored gemstone has both a top and a bottom glued to it to make a triplet. This allows, for example, a very thin piece of stone to be fully faceted. Another variation is for the entire crown, or top part, of the stone to be real, with a colorless quartz pavilion, or bottom. There are many variations on the basic themes, and all must be disclosed according to good practices and U.S. Federal law.
A new technique has recently been introduced called "Center-Fused Color Topaz". In this form, a color layer is fused, instead of glued, to the center or girdle area of the stone. The pavilion, or bottom, will typically be a colorless material. It is still an assembled stone (a triplet), and must be disclosed as such.

HEATING
Many types of gemstones are heated to produce, enhance, or remove color.
-    Sapphire and ruby (that is, corundum) are routinely heated.  Depending on the goal desired, this heating can either enhance or remove color.  It is quite common for "white" or colorless sapphire to be produced by heating from stones with weak natural color.  In addition, it is not unusual to heat corundum in order to remove or reduce inclusions (that is, to improve clarity).  In corundum, heating for all of these purposes is generally considered "usual and customary".  Heat treatment of corundum is considered permanent.
-    Aquamarine (blue-green beryl) is also frequently heated.  In current practice, this has the effect of both removing the green color component, and enhancing the blue.  This should not be considered customary, and should always be disclosed.  Nonetheless, the treatment is believed to be permanent.
-    Tanzanite is customarily heated to produce the various blue, blue-purple, periwinkle, and greenish-blue colors seen in the industry.  Virtually all tanzanite mined today is brown until treated.  The treatment is believed to be permanent.  Natural blue tanzanite -- if any really exists -- is a truly rare and near-priceless gemstone.
-    Topaz is commonly heated to produce or enhance color.  "Imperial" and pink topaz are heated to enhance their yellow and pink colors, respectively, and colorless topaz is heated (along with other treatments in some cases, including irradiation) to produce blue topaz.  (Very pale blue topaz occurs naturally, but is quite rare.  Most is enhanced before reaching the market.)  Topaz has a tendency to fade over time.  Some natural colors (particularly browns) fade quite rapidly.
-    Citrine (yellow quartz) occurs naturally in limited quantities.  Most citrine on the market today is produced by heating amethyst (purple quartz).  This treatment is considered permanent. (The amethyst-citrine color change has been recently experimentally shown in the lab to be reversible, one to the other, repeatedly.)
-    Ametrine, or bicolor amethyst-citrine, is found naturally in a small area in Bolivia.  The effect is also produced artificially by controlled heating of amethyst, causing only part of the stone to change to citrine.  Most of the ametrine on the market today is produced in this manner.  As with citrine, the coloring is considered to be permanent.
-    Apatite is virtually always heated to produce any of several colors, most notable in the market today being the so-called "neon" blue-green.
-    Zircon is commonly heated to remove color, originally producing a low-cost alternative to white (colorless) diamond.  (We use it for that purpose, but we also consider zircon -- in all its colors -- to be a worthy and beautiful gemstone in its own right.)  The treatment is permanent.  (Note that this is natural zircon, not CZ, or cubic zirconia, which is entirely man-made.)

OILING and FRACTURE-FILLING
-    Oiling is used to enhance the appearance of some gemstones.  The most common of these is emerald.  Recently, some samples of the rarer tourmaline varieties - such as the so-called "Paraíba" from Minas Gerais, Brazil - have been found to have been fracture-filled to increase their market price.  A special oil, resin, adhesive, or other material is forced under pressure into surface-reaching fractures and voids.  In some cases, the flaw may actually be enlarged by mechanical or laser drilling in order to improve the flow of the filler material.  (Usually, this will only be done on more-valuable material in order to be able to recover the obviously-higher costs.)  The filler is usually colorless, but may be colored to match the general color of the stone.  The only purpose of this treatment is to hide flaws (and incidentally, it usually enhances the color of the gemstone at the same time).  Nonetheless, it has been occurring so long (at least with emeralds) that many consider it to be "usual and customary".  However, we -- among many others -- do not.  Moreover, oiling is not a permanent treatment.  The filler material can come out of the stone in a variety of ways, usually involving heat and/or cleaning products or techniques.
-    Opal is also commonly oiled, in that it is often kept in glycerin (at least prior to cutting).  While the alleged intent is to keep the stone from drying and cracking, it also has the effect of enhancing the appearance of the material.  There is also a school of thought -- to which we subscribe -- which says that it is wrong to do this.  This is because the structure of opal is dependent on the presence of water.  The loss of water is the reason opals have a reputation for drying and cracking.  Since oils -- including glycerin -- will frequently displace water, it is believed that keeping opal in anything but water will, in fact, speed up the drying and cracking process.

IRRADIATION**
Exposure to radiation has been a source of color treatment for a number of years for some stones, and more recently for others.  For example, the spectacular "London blue topaz" is produced by a combination of heat treatment and irradiation.  More recently, diamonds are being colored by irradiation.  As with all gemstone and jewelry purchases, know your dealer.  Many irradiated stones are radioactive for a period of time, during which it is illegal to import or sell them in the US.  Nevertheless, unscrupulous dealers occasionally distribute stones which have not yet fully "cooled".  Following the required storage time, the stones are completely harmless. (see the Irradiated Stones Notes)

**AGTA and the GIA are continuing to  investigate whether or not the irradiation of mail by the United States Postal Service poses a hazard to the color or other properties of gemstones.  Results from the GIA (Spring 2002 issue of Gems and Gemology) show substantial irreversible color change to many colored gemstones.  GIA recommend use of alternative means of shipment pending further research (other than those which are most likely to be irradiated, e.g., first class envelopes, etc.). This research is still underway.

DIFFUSION
Diffusion is a means of changing the color of a gemstone, usually by heating under pressure or by vapor-deposition under vacuum, in a particular chemical environment (generally, a gas enriched in a particular element). For example, using iron and/or titanium increases the saturation ("depth" of color) in blue sapphires.  In general, this produces a color change confined to a shallow region near the surface of the stone.  Consequently, chips or scratches can sometimes expose the original color of the stone.  Some diffused stones may also fade easily because of the shallow color layer.  Several different types of stones are currently being diffusion-treated, although the most common are topaz and sapphire.   Mystic Topaz, and the many variations of it, is diffusion-treated, as are the relatively-recent teal, red, and other brilliant new topaz colors. The latest colors for topaz try to duplicate some of the popular blues traditionally created through irradiation.

More recently, a diffusion process has been developed which is capable of causing a color change virtually throughout a stone ("bulk diffusion").  This makes the change extremely difficult to detect, but also extremely durable.  Perhaps the most familiar form of this deep-diffusion treatment is to introduce beryllium into sapphire to approximate the pink-orange color of the very-rare Padparadscha sapphire.  Many vendors even sell this material as "padparascha", even though most of it comes from Thailand, not Kashmir.  A usually-reliable give-away on this material is price: real Padparadscha sapphire is extremely rare, and consequently commands a high price. This also holds true for other colors which are generally rare and valuable.  There are now many colors on the market.  Be sure you know your source, especially when buying stones which are richly or unusually colored. There is also a great deal of disagreement about whether or not this deep diffusion should be disclosed, since it appears to be permanent. A literal reading of the Fair Trade Rules makes disclosure mandatory. Gemsmiths supports full disclosure of all treatments.

Beryllium can also be used with heat treatment to improve the color in some blue sapphires. It should be noted, though, that the presence of beryllium by itself does not prove treatment by this method, since some African blue sapphires have naturally-occurring beryllium.

Another treatment for corundum is "infusion" of a lead-glass mixture under high temperature. This results in a stone which looks like high-grade Burmese ruby.

TANZANITE
Tanzanite is commonly treated by heating to produce its spectacular purplish-blue color, as well as other colors, such as a minty green. There is also a new surface treatment being used to enhance color. Since this is a surface treatment, the stones cannot be re-cut or re-polished.  We will provide more information on this new process as we find it.

Notes on Irradiated Gemstones

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