Coloured Stone Grading

[chrono]

I am new to coloured stones and need some explaination/clarification on the following:

1. Are there any standards when it comes to coloured stones? There does not seem to be any and most are sold without certification. This makes it very hard for a consumer to purchase quality gemstones. Do you think this will change in the near future?


2. I''ve heard a little about the A/AA/AAA/AAA+ grading. How are these graded? What is it based on? For example, what is the difference between AA and AAA? Why are some stones graded and others aren''t? I''ve also seen some GIA grading for gemstones but it seems very complicated to me.

 

[katbadness]

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On 7/26/2004 2:21:31 PM chrono wrote:

I am new to coloured stones and need some explaination/clarification on the following:

1. Are there any standards when it comes to coloured stones? There does not seem to be any and most are sold without certification. This makes it very hard for a consumer to purchase quality gemstones. Do you think this will change in the near future?


2. I've heard a little about the A/AA/AAA/AAA+ grading. How are these graded? What is it based on? For example, what is the difference between AA and AAA? Why are some stones graded and others aren't? I've also seen some GIA grading for gemstones but it seems very complicated to me.

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As far as I know, there is no widely accepted standard for colored stones. I believe GIA has color grading, as does AGL, but I am not certain what their acceptance is.

Here's an old thread with colored gem lab grading discussions.

 

[chrono]

Hmm, does it mean that when a person wants to buy a coloured stone, he is on his own? I mean, a person can only do so much research but we all don't have the time to be experts just to buy a few gemstones. What is our recourse? It seems that buying gemstones online and in real life is so very difficult because there is no standard on cut, colour, hue and saturation. I enjoyed the process of picking out my very own diamond but could not do the same for my sapphires because of this.

 

[bar01]

Sorry to say - but yes - you are basically on your own.

There is no accepted grading like there is with diamonds. You can get certification (difficult) - typically AGTA for colred stones like sapphires. But even these reports don't grade the stone - they only tell you the basics - the size, if it is natural, if it has been treated, etc..

So picking a good colored stone is subjective. You have to learn about things like orgin of the stone (affects price drastically), color, clarity, and if it has treatments (typical). Finally, it is difficult to find good colored stones, because everyone sells diamonds instead.

You want to see some exceptional colored gems????(price is no object) Try

www.cherrypicked.com

They have their own grading system.

Also, if you just want to browse in person and see what good colored stones look like - you can go to a "high end" store like Tiffany's. They are over priced, but you can get an idea for good color, clarity and intensity.


Also - go to www.palagems.com for some information. Also go to Amazon.com and they have a number of books on buying gems.


Good Luck.

 

[bar01]

Oh - there is one other independent colored stone lab testing agency I found -American Gemological Laboratories (AGL). They do provide grading criteria and comments on quality of the stones - unlike AGTA.

I don't know much about AGL - they don't have a web site - and I have not found many places that offer the AGL reports with their stones.

 

[katbadness]

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On 7/26/2004 4:18:24 PM bar01 wrote:



Oh - there is one other independent colored stone lab testing agency I found -American Gemological Laboratories (AGL). They do provide grading criteria and comments on quality of the stones - unlike AGTA.

I don't know much about AGL - they don't have a web site - and I have not found many places that offer the AGL reports with their stones.

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Here's a vendor who includes AGL certs on all of the listed stones.

You can even find a a small section on how to read the AGL cert, on the site.

 

[valeria101]

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On 7/26/2004 3:08:41 PM chrono wrote:

Hmm, does it mean that when a person wants to buy a coloured stone, he is on his own? ----------------

Hm... with no precise grades in place, your own eye is usually enough - simply because that is what everyone uses. Just like you would be carying a color grading set of diamodns all over

No one has (yet) the monopoly of grading colored gems, as the few major labs hold for diamonds. If there were as many rubies as there are diamodns, than life would be different - but for now, rubies just have to be eye clean and diamonds graded. Which do you preffer?

Tiny, barely there, differences in color and clarity would not make a difference for colored gems value, simply because any quality standard just reffers to what the eye can see. Questions like "is it eye clean" and "is it gray" or "is it dark" are all there is now for quality grades anywhere. Isn't that easier to spot than the invisible difference between D and E diamodns?

The best part about eye-only quality grading is that you know everyone just does this - what is strykingly beautiful to you will be so to anyone else, and for this reason valuable.

Identification is harder in the case of colored stones, and, in fact, this is all that lab certs do: testify that a certain stone is genuine material (threatments and origin included).

Granted, all this is different from what diamond shopping is - and it is simpler, not harder, I would think.

It would be fun to hear impressions from gem buying. I only have to mantras in mind:

#1. Don't listen to the seller?
#3. How does it compare to the best?
#2. Will everyone like it?

Strange? Well... let's pass #1, #2 comes from a bit of experience anyone can get from auction catalogues and museums, #3 wants to say that the gems that appeal to everyone, regardless of experience, training or taste, are the trully best

For example, with some understanding of precious stones, I might be totally in love with a rare brownish garnet but my mother would just want something glowing red! Obviously, gems of pure spectral colors are the most valuable. "Keep it simple" seems to pay in choosing colored gems.

Does this help a bit?


As for prices... what is PS good for then?

If GIA's color coding system did not hold much is that there is not that much to choose from. I do not think one could find a list of vivid blue sapphires as one can find a list of colorless diamonds... There is still some room for taste aside trade rules in choosing your perfect bit of color, I hope.

This is one more long post out of some frustration, as you would have guessed by now.

 

[valeria101]

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On 7/26/2004 3:35:28 PM bar01 wrote:



So picking a good colored stone is subjective. You have to learn about things like orgin of the stone (affects price drastically), color, clarity, and if it has treatments (typical).

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Is origin so important? When? For what?

I trully believe that color and clarity is not judged in colored stones on the same scale and using the same standard as in colorless diamonds.

And treatments are subject of certification... right ?

Maybe there needs to be more chatting about this on PS

 

[valeria101]

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On 7/26/2004 2:21:31 PM chrono wrote:




2. I've heard a little about the A/AA/AAA/AAA+ grading. How are these graded? What is it based on?

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GIA's system is not widely used, but makes a wonderful learning tool. You can get a good idea of what matters for a colored gem's value. The fastest way to get a grip of this maybe some online tutorial (Pala's ?LINK)... but the whole concept is really not complicated at all. All you need is a good source. If the one mentioned sounds ok for starters, questions are welcome indeed

The AAA...A's are done by every store - there is no standard. As there is no standard for the AAAA...A's that buyer's write in Ebay feedback. One can well pretend they do not see these

I like how Tiffany's tutorial on pearls explains what these AA's are all about.

It is just one paragraph: Take a look

Hope this helps

 

[katbadness]

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On 7/26/2004 5:56:31 PM valeria101 wrote:

Is origin so important? When? For what?

I trully believe that color and clarity is not judged in colored stones on the same scale and using the same standard as in colorless diamonds.

And treatments are subject of certification... right ?

Maybe there needs to be more chatting about this on PS

----------------

I think the origin matters only as much as how much you put value into the 'romance' and rarity of stones from certain origin itself.

However, as Mogok described just a few posts ago, apparently rubies from certain other areas frequently passed as 'Burma' rubies.

Do people *also* end up paying undue price because said stones are claimed to have come from a more famous origin?

To me, this then begs the question of the accuracy of the labs. For those who care about origins, the labs, then have to be quite vigilant about being able to provide a relatively accurate opinion-report for stones from certain origins (i.e. Mogok, Kashmir, etc.).

I am a strong proponent for more color and clarity grading on PS. Maybe using the Munsell color system?

But then we run into color viewing problems (lighting condition when pictures are taken, monitor difference, etc.).

I'm crossing my fingers, and I have a lot of hope though..

Who knows, we may even start people in the colored gem trade to notice that buyers are interested in some standard color and clarity grading.

 

[valeria101]

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On 7/26/2004 6:15:42 PM katbadness wrote:

Do people *also* end up paying undue price because said stones are claimed to have come from a more famous origin?

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Origin is not routinely identified by colored gems certs - it is an ambiguous and imprecise exercise when it does happen: some pieces can be positively identified, some not regardless of type and actual source...

The one rule that seems to be cited often sounds like: "origin is no excuse for flaws, but a good reason for a premium". Meaning, in fact, that pedigree does make a difference only between two top specimens.

For anything but the best, it's up to the buyer - one may want origin and pay for it, but there is no guarantee that you will find another buyer so inclined to willingly offer a premium for your taste.

You are right to say that sometimes claiming origin is used as a sales tool... but this is usually not great news.

Of course, this is my gut feeling and imperfect knowledge talking, as usual.



I wish I knew more cases of discrimination against top Zambian emerald that just failed to be Colombian, or top Burma sapphire that failed to be from Kashmir, or perfect African ruby that failed to be from Burma...in anyhing but rights of birth. Unfortunately, I just do not know of too many major stories. Any help?

PS: I hope I will not see a color system used on colored gems during my lifetime... Actually, diamonds could be treated in the same way: just define an interval of color saturation from "nothing much" to "nil"! There is good reason why they are not

 

[bar01]

Great discussion. Everyone should know that I am just a Newbie to the colored stone community - so be easy on me! I am just sharing my thoughts!

I have purchased a book on Rubies and Sapphires. I have also been reading a lot of web sites and old discussions on PS.

Let me respond to the discussions that took place about origin (my early comment on price). Obviously, you should pick a stone that you like. Good color and clarity can come from anywhere. There are bad stones from good locations and great stones from lesser known areas. It is also true that it can be difficult to accurately determine origins. AGTA will try to do this for an extra fee - but it is no certainty.

However, the general (and I do mean general) statement in the book I bought and what I found on some other sites is that when it comes to general pricing for Sapphires – the top is Kashmir and Burma. Slightly less - but still good - is Sri Lanka/Ceylon. Then there is everywhere else. This is a general statement – different regions have different mineral and geological properties that have tended to produce different looking sapphires than other areas. Also some regions are no longer producing stones like they did in the past and so these stones are considered more “rare”.

Choosing a fine colored stone (like a Sapphire) is a very personal choice and made difficult by lack of accepted grading. Origin may not mean anything to some people – instead they want to focus 100% on quality (cut/color/clarity/etc.) and what looks good to them. However, when determining what to pay for that good looking stone – you should, in my mind, include some type of factor for the origin in determining what is a fair price for that stone.

Of course I won't even go into the other picing issue - treated vs untreated Sapphires.


Anyway - just my two cents on this issue.

 

[chrono]

Wow, I'm glad this spawned a lot of replies overnight!

I too think an accepted colour and clarity system will help confused consumers like me select/ be able to better buy my own coloured gemstones. Then, if a person happens to like a different colour which may be certed as a less desireable gemstone, then pocket the savings and enjoy what you prefer. Or at the very least, there is a need for better and standardized definitations for colour and clarity grading. The next question is how do we or anyone else for that matter, convince the sellers that this will be a helpful tool?

 

[mogok]

Hello,
Well that's funny that a discussion about a color grading system arrives here as there was just an excellent discussion about that on yourgemologist.com:
http://www.yourgemologist.com/phpBB2/viewtopic.php?t=747

The fact is that to have a serious grading system for colored stones is nearly an impossible task due to the diversity of varieties, colors (monochroic, dichoic, trichroic, with or without dispersion...) that it will probably never be accepted by everybody. Color stone grading is one of the pandora box of the gem trade: Open the subject: everybody is agree that there is a need for that... Propose something: everybody will shoot you down and many times with good arguments. Its very difficult...

I think that to grade beauty and art is such an impossible task. It is so subjective. You can give an opinion, that's something but to label your opinion a grade... well...

All the best,

 

[Richard Sherwood]

The GIA & AGL both have recognized color and clarity grading systems for colored stones. The AGL (American Gem Laboratories) has a cut grading system as well, and the AGL certificate is highly respected among gem dealers. The SSEF report put out by the Gubelin lab in Switzerland is highly regarded, and has made groundbreaking progress in describing such things as the level of glass resin filling present in a stone on a scale from minor to moderate to significant, as well as indicating (like several labs do) the presence or absence of heat treatment.

Although the GIA has a very helpful colored stone grading system, as far as I know they don't use it on their reports. The AGTA puts out a respected report, but as far as I know they are similar to the GIA in that they don't put out a quality analysis on their reports. The Gubelin report I'm not sure of, but haven't seen any with a "quality" analysis.

I use the GIA's system on my reports for color/clarity, and then my own analysis regarding cut. The GIA system, properly used, will go a long way towards conveying the overall quality of a gem. The AGL system does the same thing, using a little different terminology.

The GIA system breaks down the color description into (3) components: Hue, Tone & Saturation.

Hue: Root body color

Modifier: Secondary modifying hue(s), on a scale ranging from "very slight to strong", (ie "strongly purplish Red", abbreviated stpR)

Tone: Light to Dark on a scale of 1 to 10
0- colorless or white
1- extremely light
2- very light
3- light
4- medium light
5- medium
6- medium dark
7- dark
8- very dark
9- extremely dark
10- black

Saturation: How pure or desaturated by gray or brown the hue is on a scale of 1 to 6- Vivid (6), Strong (5), Moderately Strong (4), Very Slightly Grayish or Brownish (3), Slightly Grayish or Brownish (2), Grayish or Brownish (1)

Clarity is desribed in a similar manner to diamonds, with this distinction. They recognize that different types of minerals typically crystallize in heavier or lesser included states. For example, Aquamarine typically crystallizes in relatively clear crystals, while Emerald or Red Tourmaline typically crystallizes in relatively included (imperfect) crystals.

Therefore, they adjust the clarity grading system in three types-

Type 1: Typically crystallizes inclusion free (such as aquamarine & topaz)
Type 2: Typically crystallizes included (such as ruby, sapphire & garnet)
Type 3: Almost always crystallizes included (such as emerald & red tourmaline)

The Type 1 category is graded almost similarly to diamond clarity, while the Type 2 and Type 3 categories are supported by a "handicap" system. In other words, a VS quality emerald will be a "clearish" clarity, but nowhere near as clear as a VS clarity aquamarine.

The different types are then clarity graded with the familiar, although slightly modified clarity terms used in diamond clarity grading:

Clarity
VVS- very, very slightly included
VS- very slightly included
SI1- slightly included, first class
SI2- slightly included, second class
I1- included (imperfect), first class
I2- included (imperfect), second class
I3- included (imperfect), third class
DeClasse'- stones not transparent because of inclusions

The AGL lab uses a similar system with different terminology:
Flawless- eyeclean
LI1- lightly included, first class
LI2- lightly included, second class
MI1- moderately included, first class
MI2- moderately included, second class
HI1- heavily included, first class
HI2- heavily included, second class
EI1- severely included, first class
EI2- severely included, second class
EI3- severely included, third class (DeClasse')

Note- The AGL does not use the three Type category system which GIA uses.

Cut, or Make SGL grades cut on a categorized system of:

Exceptional
Very Good
Good
Fair
Poor

Most "native cut" stones fall in the "fair" category, with some ranging from fair to good or fair to poor. Usually when you see a very good or exceptionally cut stone, it was cut in Israel, Europe or the United States. Note- A "fair" native cut stone can often be quite beautiful, lacking only the preciseness of cutting which is often typical of the precision consciousness of Israeli, European & Western cutters. Richard Homer and the German Idar Oberstein precision cutters would be an extreme example of this "cut consciousness".

Brilliance
This is another aspect of make which is graded when examining the a colored stone:
Brilliance how much of the surface area "returns light" or "shows color".
Extinction how much of the surface area "absorbs light" or "goes dark".
Windowing how much of the surface area "leaks light", creating a "window" through the stone.

Using these established parameters, a gemologist can usually convey the "fineness" of a gem to an extent that another gemologist or savvy consumer would be able to recognize it. Multiple photographs from different angles and under different lighting conditions are also helpful, although nothing substitutes for an actual visual inspection.

 

[Rank Amateur]

Wow. Great post Rich. Thanks.

Maybe I should write "Thanks!" on the back of a $20 bill and send it to you?

 

[Richard Sherwood]

Yes, if you're all out of hundreds, that would work fine.