Colored Stone Grading

[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 lab (American Gem Trade Association) 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.

 

[bar01]

Excellent Richard!

You know as a consumer, I have found some the lack of an accepted standard grading system frustating. I applaud GIA and AGL for taking the lead in attempting to have something for us simple folk.

I think one of the giants in the field of Ruby and Sapphires - Richard Hughes said it best in his authoritive book- about the resistance of some to grading systems (note: the information below is public domain).
------------------------------------------------------------------
Ruby & sapphire Grading: A heretic’s guide

Having now committed one heresy, the discussion of religion, I shall proceed to commit another, discussion of colored stone grading.Comparable to those who opposed the mere thought of Columbus sailing into unknown waters, today many traders and gemologists oppose even a discussion of systematic quality analysis of colored stones. Akin to the priests of the Middle Ages, who fought against translation of the Latin Bible into vernacular languages, these high priests of the gem trade apparently feel that only those properly initiated into the “Great Order of Gemmarum et Lapidum” should be allowed to dine at the quality-analysis table. Others less fortunate must be content to scramble for the crumbs of knowledge those on high deem suitable to toss their way.

Grading systems are as old as the gem trade itself. Witness ancient India’s Garuda Purana, dating back as far as 400 AD (Shastri, 197, which classified the then-known gems into categories on the basis of their characteristics. Over the succeeding centuries, these systems have been steadily refined. Diamond grading systems made their appearance in the 20th century, but modern attempts at colored stone grading date only from the late 1970s. Problems with some of these early attempts have led many to condemn the very idea of systematic grading. In the author’s opinion, this is a mistake.

Early forays into colored stone grading were primitive, and today many problems remain. This is to be found in the development of anything new. Look at the first airplanes. Clumsy and dangerous, they often killed their occupants. Today few would argue against their use, but in the beginning many did: “If humans were meant to fly, they would have been born with wings” was the typical refrain. I suppose if humans were meant to drive, we would have been born with horns and bumpers.

In his excellent article on the methods and benefits of colored stone grading, Nelson (1986) cataloged a large variety of trade objections. In this author’s (RWH) opinion, the key criticisms are threefold:

Like the priests who opposed translation of the Latin Bible into common languages, dealers are afraid that colored stone grading will remove their trade advantages, thus cutting the traditional gem dealer out of the picture.

In a business where the most complicated and expensive piece of equipment is often an electronic balance, traders dislike the thought of having to send their stones out for lab grading.

Many colored stone dealers abhor the thought that their trade might become like the diamond trade, where stones with certificates are traded in an indiscriminate manner, in some cases without ever viewing the gem. As a Geneva dealer once told me: “My five-year old son can trade certificate diamonds. It requires no knowledge, no training.” This is a real problem, one which gemologists must answer before they can gain trade support for colored stone grading.

Unfortunately, the advantages to such a system are too often overlooked amidst the bluster and rhetoric. These benefits are the increased consumer confidence and thus, increased sales, which would follow adoption of such standards. Much time would also be saved by adoption of a standardized language for describing the appearance of colored gems.

The key to developing a successful colored stone grading system will be in creating a language useful for communicating the overall appearance of a gemstone. Once a gem is adequately described, it is then up to the marketplace to determine relative value. Attempts to assign relative values to each grade will succeed only if the considerations of the real marketplace are taken into account. To make these decisions, gemologists must work closely with traders.

An unfortunate paradox in the gem world (and one which is also present in many other fields) is that traders, who, by virtue of experience, are generally most qualified to judge quality, must be disqualified from doing so because of their bias. But traders must have input into the system for it to succeed

 

[denverappraiser]

Richard,

Good work. Thanks.

You describe the GIA/Pantone system very clearly. Does AGL use the same system for the basic color description?

Neil Beaty, GG ISA
Independent Appraisals in Denver

 

[elmo]

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On 9/22/2004 11:37:55 AM denverappraiser wrote:


You describe the GIA/Pantone system very clearly. Does AGL use the same system for the basic color description?
----------------

AGL uses something called Color Scan, which is different from the GIA system and proprietary from what I understand. It reports color as a dominant color and two modifiers (as percentages totaling 100) plus a tone, also a percentage. I see on Dave Atlas' resume that he has the Color Scan system in his lab, so he might be able to answer some specific questions as well.

 

[yowahking]

While Bar01 is light years ahead of most industry people, (sure you are a consumer?), and Richard gave some great insight on labs, I have another angle. I spend several weeks a year overseas on buying trips. I have learned from books, GIA, seminars, etc. I learn way more from the dealers when I am actually buying. 4th generation Ruby dealers do not need a lab report to tell you which of 10 stones is the best one. Just as a top level carpenter does not need someone to tell him which piece of wood will produce the best result. I am a firm believer that most people, jewelers and consumers are lazy and want to rely on someone else to do the homework on a gem so they don't have to bother learning anything. While colored stones are infinitely more interesting and difficult to understand than diamonds, most people are smart enough to get it once explained. I brought one of the best experts in the US on colored stone treatments to AZ to teach jewelers and employees the latest info. The seminar was very cheap, so price should not have been a factor. With 300 stores invited, guessing at 3 employees per store, we had hoped for a 10% response of 90 to 100 people. We got 21. 5 of 21 were from my store. So the TV channels will survive for a few more years promoting BS and crappy gems.

 

[valeria101]

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On 9/24/2004 11:36:49 AM yowahking wrote:



4th generation Ruby dealers do not need a lab report to tell you which of 10 stones is the best one.

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

Otherwise there would not have been a second generation of dealers in the family, let alone a fourth

Even with a grading system in place though, all an inexperienced person can do is shoot for the highest grades for safety and pay whatever asked. Precise grading just makes clear just how high a rink premium the average buyer would pay to make sure his choice is 'right'.

How can one random buyer gain access to a representative inventory of gems of any kind and learn what the grades mean ?

 

[cflutist]

I have two questions that maybe the experts can answer.

I just had my blue sapphire (<== link) recut by Richard Homer.
Wink and Richard have been telling me for the last week how honking gorgeous the stone is.

I read the appraisal and the color is bV 5/5 by the GIA color grading scale. Note, that Wink did use the "GIA Gemset paddles - 324 color comparators categorized by tone and saturation within a given hue" when he graded this stone. I whip out my charts from the GIA Colored Stones Grading Class that I completed back in 1989, look up the bV 5/5 (bluish Violet, Medium Tone, Strong Saturation) and it says its a color grade of 4.5 out of 10.

To me 4.5 out of a possible 10, that means mediocre in color ... and to be a "10" you need a vB 6/6 or a B 6/6. What am I missing here? I don't know if I would really want the stone to be darker in tone? Am I misreading the charts?

So I have two questions for the experts:

1 - why is this beautiful stone only a 4.5?

2 - has anyone seen a vB 6/6 or B 6/6 and what does the color look like.

 

[chrono]

I am making some guesses here. I think colour grading is subjective. Just because your sapphire rates a 4.5 out of 10 doesn't mean that it isn't beautiful. It is obviously gorgeous to you. You may think a vB6/6 that is rated a 10 is too dark while another person thinks it's just perfect. I also prefer lighter shades. One website that helps me compare various colours is:
Awesome Gems

I know that colours view onscreen is different but at least it helps to have some sort of reference.

 

[Richard Sherwood]

-----------
1 - why is this beautiful stone only a 4.5?
-----------

It's not. That's the limitations of generic charts, they can't account for the exception to the rule. It takes a human being to be able to recognize it.

Your stone formerly looks like it was in the 4.5 neighborhood for quality (medium commercial grade). The custom cutting has raised it from a medium commercial grade to a fine grade, probably in the neighborhood of 7 out of 10, with a subsequent increase in value over that of the re-cutting charge. Gorgeous stone.

The 9 and 10 grades are reserved for a tone of color one shade darker (medium dark) and one shade more vibrant (vivid saturation). These stones literally ooze a bright, saturated blue hue.

Interestingly enough, the concave faceting seems to show best in medium toned stones. It turns ugly ducklings into swans.

 

[Jennifer5973]

Rich, I have a very dark 3 ct oval sapphire (not as nice as cflutist's)currently set in a "Princess Diana" type of ring with diamonds all aorund it. I had this stone thought might benefit from this type of recutting--it is very dark--blue/black. Your post seems to suggest it might not be worth it to try to recut a dark stone. Can you please share your thoughts?

Many thanks!

 

[Richard Sherwood]

Hi Jennifer. It seems that the "shimmer" and "scintillation" of the concave faceting cut doesn't show up as well in the very dark toned stones.

That's not to say that Richard Homer couldn't make your stone livelier. It's possible he could reduce the depth to lighten the tone, and then apply the most appropriate facet pattern to best enhance your stone.

Wink probably has some experience in regards to this.

 

[Jennifer5973]

Thanks, Rich. I will ask Wink to look at this picture and give his opinion. It's not a bad ring, and if I could get more life into the sapphire, I'd wear it more often.

 

[Jennifer5973]

This is a better picture:

 

[Richard Sherwood]

Gorgeous.

Ring's not bad either...

 

[WinkHPD]

If the stone is as dark as shown in the picture it will NOT benefit by Richard's cutting, only because the light will not be able to get through the stone to take advantage of the now magnificent cutting.

Sorry. If the stone is a tone or two lighter than it shows, then it might be a candidate.

Wink

 

[Jennifer5973]

Aw, Rich--you're such a lady's man.

Wink--thank you, as always, for your honest and expert opinion. I will look at the stone/ring and see if it is worth sending to you for further evaluation.

 

[WinkHPD]

Rich,

Thank you for your thoughtful and kind reply to Cflutist. In using the color paddles I am restricted to choosing that paddle that most closely resembles the color of the stone, and for this stone it was as noted above. To think that it was only a 4.5 on a scale of 1 to 10 would be absurd, yet that is what the chart says.

Maybe someday, it would be nice to see before I die, someone will finally develope an accurate way to judge and to convey color in something other than the D-M colored diamonds. In the meantime it is nice to have someone like you around to explain these seeming conundrums to our friends and clients. You were able to give her much peace and understanding of what I was trying to share with her with the added bonus of being an unbiased observer. I just want you to know that I appreciate it just as much as she does.

Wink

 

[cflutist]

Rich and Wink, thank you very much for your expert explanation. It was very much appreciated.

The instructions for using the GIA Color Grading Charts (c1989) say:
GIA established color grades through a broad survey of the colored stone market. They represent GIA's estimates of a generally accepted order of preference. There is enough diversity in the market to allow a range of plus or minues one grade, especially in the middle range. New data may bring modifications in the future. You should be aware of variations in the international market and be prepared to make your own judgements.

Well maybe its time for a modification? The 4.5 grade (out of 10) for my bV 5/5 is a little harsh.

 

[WinkHPD]

I don't know any one in the trade who pays any attention to that chart. (I am sure I know some who do, but none who have ever ever mentioned it to me when I was buying or selling a stone with them.)

There simply is not an adequate way of describing color and color nuances that has been accepted by any large number of people, in spite of millions of dollars of efforts by such groups as the GIA and AGTA.

That chart is worth the paper it is written on and when put into experienced hands maybe a little more, but not much. (This is strictly my opinion here, not necessary to have me quartered and drawn if you disagree)

Color is, and for the foreseeable future will continue to be subjective. I will give more value to your stone than some other vendors and what they treasure I may not. It is such a personal thing as to what color and what intensity of color is the most pleasing, and although the market will have some consensus as to what is valuable, there will never be a unanimous consensus on each and every shade and hue.

Wear your stone well and treasure it, it is worthy of being treasured, regardless of the limitations of our ability to describe it.

Wink

 

[cflutist]

I think the problem lies with human nature. We like to quantify things:
e.g. your SAT/GMAT/LSAT scores for admission into college/grad/law school, your GPA, the sq of your home, the HCA score (heck you would poo-poo a HCA=4.6 that still is a beautiful stone, but love a .9) of a diamond, the carat weight of your stone (measured to a thousandth of a carat and rounded to the closest hundreth only if its .xx9 e.g. 2.568 = 2.56 ct, but 2.569 =2.57 ct.

I guess the challenge with colored stone grading is that we are trying to translate into numbers something which is subjective in nature. Thank you Richard and Wink for setting me straight. I am at peace now with my sapphire.

 

[valeria101]

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On 10/1/2004 2:11:27 PM cflutist wrote:

I think the problem lies with human nature. [...]
I am at peace now with my sapphire.
----------------

Well. well... there are no standardized scores for college down here (admision exam instead). IQ-type scores are illegal (anti-discrimination law).

GIA's system for communicating color is nice to know but their value judgement just favors the night sky over day. Kind'a crazy

 

[windowshopper]

Richard/Wink --
I am considering buying a sapphire from Walter Arnstein--they claim all their sapphires to be unheated and all have certificates from AGTA. Is this good enough? If I am going to spend a lot of money on a top sapphire is there anythimg else i should do to make sure its really a worth what I am spending?
Thanks
WS

 

[Richard Sherwood]

Sounds like you're off to a great start, W.S.

With the AGTA report you'll have all treatment issues disclosed, along with other helpful information.

The only other thing I would suggest is having the sale made contingent upon the sapphire appraising out to your satisfaction, with a right of return for any reason within a reasonable period of time (10 days?).

 

[windowshopper]

do you do appraisals on unset colored stones?

 

[Richard Sherwood]

Yes. Love doing color, and I have considerable experience in ruby/sapphire.