(AGL) American Gemological Laboratories became the first laboratory in the world to quantify colored stones in a linear, comparative manner. They are the leaders in gemstone documentation and have extensive experience in consumer protection programs.
The grading system which they created is very comprehensive and requires some knowledge to understand. However, once you grasp the foundation, you will be able to communicate to anyone in the diamond or gemstone industry.
Document Number:
This is a gem specific number for each grading report issued.
Image:
A digital representation of the stone assists in verifying the gemstone matches the grading report. This image does not show actual size or body color. Our technology, lighting and printing isn't "life-like" yet.
Identification:
This tells the owner if the gem is natural, synthetic or altered.
Shape and Cut:
Self explanatory but can go further in-depth when it comes to fancier cuts like "hearts on fire".
Carat Weight:
Colored stones are weighed with an extremely accurate scale.
Measurements:
Measurements in millimeters.
Color Scale:
1 - 2 - 3 - 4 - 5 - 6 - 7 - 8 - 9 - 10
Excellent - Very Good - Good - Fair - Poor
Since there are so many optical/physical principles involved in the reflection and re-reflection of light through a gemstone, any particular gem can exhibit a wide range of colors. The color grade is based upon the purity of primary, or body color.
Fun Fact on Color Grade:
Asking for 1.00 to 2.00 color grades of a particular gem is a waste of time Because of the AGL's strict grading practices, a 3.5 color is usually the best color grade any gem will receive. On occasion you may find exceptional gems that will receive even better color grades, but that is rare.
Tone Scale: (in percentages)
0 - 5 - 15 - 20 - 25 - 30 - 35 - 40 - 45 - 50 - 55 - 60 - 65 - 70 - 75 - 80 - 85 - 90 - 95 - 100
Very Light - Light - Light Medium - Medium - Medium Dark - Dark - Very Dark
Tone describes the lightness or darkness of a gemstone. If a stone is too light in tone, the color will not be rich enough, but if a stone is too dark, it will sacrifice transparency and brilliancy (depending on gemstone).
Clarity Scale:
FI - LI1 - LI2 - MI1 - MI2 - HI1 - HI2 - E1 - E2 - E3
Free of Inclusions - Lightly Included - Moderately Included - Heavily Included - Excessively Included
Clarity is defined as the degree to which the stone is free of inclusions.
Fun Fact on Clarity:
You will probably not see inclusions in a LI (Lightly Included) gem, you could see some inclusions in a MI (Moderately Included) gem, and you will see inclusions in a HI (Heavily Included) gem. E (Excessively Included) gems have durability issues and should be avoided at all costs.
Depth:
The depth of the gemstone from top to bottom.
Cutting and Finish Scale:
1 - 2 - 3 - 4 - 5 - 6 - 7 - 8 - 9 - 10
Excellent - Very Good - Good - Fair - Poor
Fun Fact on Cut and Finish:
Unlike diamonds which are cut according to strict parameters, many colored gemstones are cut for weight retention and body color retention. So don't overlook a gem because of it's cut. You could lose a beautiful gem.
Average Brilliancy:
Brilliancy is the amount of play the gem displays. Most diamonds are 100% brilliant while the average gem displays only of 50%.
Comments:
The comment section is very critical area because it generally designates the country of origin, any treatments the gem has been subjected to and if it is natural or not.
Total Quality Integration Rating:
It's the total visual impact of the gem into a textual description and wouldn't have an effect on the value. It couldn't... but there were times it did.
Ideal Parameters:
There are many professionals that will explain the run-of-the-mill parameters but these parameters don't cover every gemstone. In many cases people will walk away from a beautiful gem because the sales person stayed within the parameters.
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