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Telling the difference between a natural, no oil emerald from the one which has been “enhanced” with oil or resin or dye is a very important skill any emerald buyer should know before going out there to buy one.   Depending on the level of treatment and/or type of treatment, there are significant different price points as the treatment does provide clues as to how rare a particular emerald is.  For example, an exceptionally high quality emerald above 5 carat size which is untreated (no oil or resin) could fetch prices above US$50,000 per carat!  An example of this just happened recently last year on May 29th, 2012 Christies Spring Hong Kong sale auction which sold a “7.05ct Colombia, no oil rectangular-cut emerald and 9.04ct E VVS2 rectangular-cut diamond ring” for realised price of HK$8,420,000(US$1,090,080)… Assuming both diamond and emerald prices were split 50/50, the emerald would have cost around US$500,000 or over US$70,000 per carat!  However, lower quality emeralds which have been “significantly” treated with oil, dye and resin can fetch prices of around US$10 per carat!  Therefore, understanding what to look for and checking the authenticity of the certificate can make a difference between buying an emerald which you got a great deal for and buying a gemstone that you got scammed for  as the seller did not inform you what type of treatment the stones has had and how the stone has been treated.  I hope this guide will provide you the basic understanding in how to distinguish the different type of treatments.  I do want to emphasize that even if you read this guide completely and understand the basics, it does take years of experience of seeing emeralds to truly understand and distinguish the different treatments.  If there is any doubt in your purchase — even that slight 1% chance — it is always best to double check the stone from a reliable gemstone laboratory or trustworthy gem dealer.

Emeralds in General

Almost all emeralds in general are treated with filler substances like oil, resin or combination of multiple substances.  The trade estimates that more than 99 percent of emeralds have some treatments in them.  In terms of hardness, emerald crystal itself is relatively hard, but is softer in comparison to other big color gemstones like rubies, sapphires and diamonds.  The emerald crystal has a mohs hardness scale of around 7.5 to 8.0.   However, almost all emeralds have some inclusions or fractures in them because that is how the crystals are formed naturally along with the harsh techniques used in mining them.  That is the reason why GIA classified them as Type III gemstones, which are considered natural color gemstones that are “naturally included”.   So, please don’t run away if you do see an emerald with inclusions in it.

Also, the whole process of how emeralds come from rough to finish product does not allow it to be “not treated” with oil or resin.  When rough emeralds are mined, almost “all” are immediately thrown into a barrel of oil.   When cutting them, the cutter will keep oil to lubricate it.  Finally, when the trader or wholesaler wants to sell it, they will soak the emeralds again in oil or other substances.  They can use the colorless kind (accepted in the trade) or enhanced color oil (not accepted) or resin (almost impossible to remove) to improve the clarity and therefore “can” command a higher price than original “less” treated stone.  So, now you know why almost all emeralds are treated!

It is also important to remember that once you do buy an emerald, always be careful when sending it to the jeweler or cleaners who use ultrasonic or steam to clean the stone.  Ultrasonic vibrations can weaken the emeralds which are already-fractured and hot steam can cause oil or unhardened resin to sweat out of the surface-reaching fractures.  Therefore, gentle scrubbing with warm, soapy water is the safest way to clean emeralds.

No oil, No resin, 100% Natural Emerald

Natural emeralds which are not treated are ‘rarest of rare’ color gemstone and as you have read above command astronomical prices!

So, how do you know if your emerald has no oil or resin in it?  It is actually very simple! Just find one which has no fractures at the surface, so no oil can get inside the crystal or stone!  This will guarantee the emerald doesn’t have any oil because the crystal itself is so clear or protected (no fractures reaching the surface), so there is no chance for any “foreign” substance to enter the stone.

To check this you have to use a natural gem day light (or tube light) or natural sunlight and tilt the emerald in such an angle so that the light reflects from the surface of the stone (reflected surface looks white).  Then with your microscope (or gem loupe though it is a little more difficult) you can see if there are any dark lines or indented lines from this reflective surface and if yes this indicates there are some fractures reaching the surface and therefore almost 100% probable that some foreign substance has entered the emerald.

Area highlighted in yellow shows the reflective light look & the dark lines which proves this emerald has fractures reaching the surface.

Area highlighted in yellow shows the reflective light & the dark line, which proves this emerald has fractures reaching the surface. This emerald probably has foreign substance in the stone.

However if you do not see anything, anywhere in all facets then you might have in front of you the most rarest of rare gemstones!

2.87 carats Emerald No Oil v3

Emerald which we have in stock that has “no oil, resin or any foreign substance” as there isn’t any fracture reaching the surface of the stone.

Therefore, if you do come across an emerald that has no oil, no resin or no treatments and has a clear crystal, you should actually sit down and “savior” the sight of it because they are exceptionally rare and to find a replacement with these characteristics is almost impossible!

Minor, Moderate or Significant Treatment Emeralds

Distinguishing between different levels of treatments in emeralds is a very difficult task and does require time and sophisticated equipment to tell what type of fillers are in an emerald.  As explained above, most emeralds are treated multiple times and therefore will most probably have multiple filler types in them.

However, if you do have a microscope with dark field illumination (& fiber optic light), you can usually see the presence or absence of filler by tilting the emerald back and forth from front view and side view and look for some “visible color flashes.”  Again, you should check for these flashes along the fissures that reached the surface of the emerald (the process in finding these surface reaching fissures is explained in the section above “No oil, no resin, 100% Natural Emerald”).

Filling substances flashes orange in this image.  (Photo by: R.W. Hughes)

Filling substances flashes orange in this image. (Photo courtesy by: R.W. Hughes)

If you do see this you know this emerald has some foreign substance inside.   Again, this will not specify the type of filler, but it will let you know if there is any filler present or not.   Another way to detect filler presence is by checking the emerald under fluorescence light and watch for foreign material to fluoresce (only sometimes).  However, not all emeralds’ fillers flash or fluoresce, so this again is not a 100% reliable test.

So, next step after checking for the above clues, trained gemologists then actually start looking for fillers inside the emerald.  This skill requires some training and experience as distinguishing between fillers from natural liquid inclusions is quite difficult.   Descriptions in what to look for both natural emeralds and fracture-filled emeralds are described below.

Natural Emerald Inclusions include the following characteristics:

  • Liquid-filled inclusions
  • Fingerprints
  • Two-phase and three phase inclusions
  • Angular growth zoning
  • Tube-like and needle-like inclusions
  • Mineral inclusions including pyrite crystals, calcite inclusions along fractures and biotite flakes

Fracture-Filled Emerald inclusions look like:

  • Flash effect of various colors like orange to pinkish purple flash, blue flash or yellow-orange to blue flash.
  • Oil might have a slightly yellowish or brownish color (Be careful not to confuse this color with oxide staining in fractures)
  • Decomposed oils might leave whitish or yellowish branch-like patterns
  • Might see trapped bubbles in the filling material, flow structure or whitish, textured cloudy areas.

    Gas bubble inclusion seen next to natural emerald inclusions.  Proves filler substance inside the emerald.  (Photo courtesy by: R.W. Hughes_

    Gas bubble inclusion seen next to natural emerald inclusions. Proves filler substance inside the emerald. (Photo courtesy by: R.W. Hughes)

How do the labs classify “minor, moderate or significant” filling in emeralds?

There was study done by GIA in 1999, explaining their process in standardizing amount of filling inside emeralds as minor, moderate or significant filling.  What they concluded was it was easiest to standardize this inspection process by actually classifying the treatment within three categories and by making it similar to diamond grade system as it is already understood by most parties – gemologist, traders and end consumers.

So, when GIA gemologists check emeralds in the lab they classify the amount of filling inside the emeralds as described below:

1) Minor – if the presence of filled fissures substances that would fit into VVS2 to VS2 diamond clarity range (again this clarity range is for the amount of filled substance inside the emerald and not clarity of the stone)… In laymen’s term not too much substance filled inside the emerald and so the foreign substance has not change the clarity of the emerald in significant amount.

2) Moderate – if the presence of filled fissures corresponds into SI1 to SI2 diamond clarity range.

3) Significant – if the presence of filled fissures corresponds into below I1 diamond clarity range.

Clarity enhancement as classified by GIA.  These images were taken from the report issued Gems & Gemology Winter 1999 issues.  (Photos were taken by Maha Tannous)

Clarity enhancement as classified by GIA. These images were taken from the report issued Gems & Gemology Winter 1999 issue. (Photos were taken by Maha Tannous)

Again the above criteria doesn’t mean the emeralds are less included or more included but only states how much foreign substance has “gone” inside the emerald crystal.  To clearly understand these please look at the image above provided by GIA.

Another big lab in color gemstone trade that classify emeralds similar to above criteria are GemResearch Swisslab.

Our Recommendation:

When buying an emerald it is very important to check how much of the stone has been treated as this will affect the price of the stone.  If you are buying an emerald that isn’t too expensive maybe getting a verification certificate from the above labs (GIA or GRS) will be overkill in terms of price and time.  However, if you are looking to acquire an emerald which has “no oil or resin” or has “minor oil or resin” treatments, which commands a much higher price in general, you should consider getting these emeralds certified by these labs as they will specify the amount of treatment seen in the emerald.   We also recommend that for any emerald you buy, you should have a third party certificate given with the stone – i.e. AIGS or GIT.  We would not suggest using the smaller labs as they don’t have equipment to distinguish between accepted “colorless oil” from higher level treatments like color oil, dye or resin.

We also recommend when buying less expensive emeralds to ask pointed questions to the salesperson or dealer regarding treatments and observe how they respond.  If they genuinely know what they are talking about in terms of knowing what type of treatment or NOT knowing exactly the treatment inside that particular emerald, but bring up similar discussion points as shown above then you know the person you dealing with is genuine or knowledgeable and therefore, the emerald you are acquiring will most probably be accurate as well.  However, if the person you buying from states that their emeralds are “not treated” and only 100% natural and never ever have been treated, either they don’t know what they are talking about or they are not trustworthy and therefore we advise to tread carefully with these people or to avoid dealing with them completely.

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