AGL provides independent colored gemstone identification reports on emeralds, rubies
& sapphires.
The American Gemological Laboratories (AGL) Colored Stone Grading Report
How to Determine the Quality of a Colored Gemstone
The grading system which AGL devised provides a comprehensive framework for evaluation
of gemstones.
The following "walk through" of a 3.11 Burma sapphire grading report will
help you understand the various components of an AGL laboratory report. For reference,
grading scales and ideal gemstone parameters
are included below.
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Document Number |
The lab assigns individual, consecutive numbers for each grading report issued.
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Image |
A color digital image of the stone is an important part of the grading report. This
image assists in verifying the gemstone matches the grading report. Please note
the image is for representational purposes and is not necessarily the actual size
or color.
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Identification |
In this sample, the AGL has determined the stone is a natural sapphire.
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Shape and Cut |
The stone is an oval cut in this sample.
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Carat Weight |
Colored stones are weighed with an extremely accurate scale. In the sample, the
sapphire weighs 3.119 carats.
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Measurements |
The measurement of the gemstone in millimeters.
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Color |
Gems can exhibit a wide range of colors. See AGL Color Rating Scale
below |
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Tone |
Tone describes the lightness or darkness of a gemstone. In the sample above the
sapphire's tone is 75. See AGL Tone Scale below |
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Clarity
|
Clarity is defined as the degree to which the stone is free of inclusions. In the
sample the clarity is MI1. See AGL Clarity Scale below |
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Depth |
The depth of the gemstone. |
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Cutting/Finish |
The cutting grade numerically describes the overall appearance of a gem, while finish
grade refers to the polish of a gem. In the sample the cutting and finish are both
3 (Very Good). See AGL Cutting/Finish Scale below |
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Average Brilliancy |
Brilliancy is the amount of flash the gem returns to your eyes. Most diamonds are
100% brilliant. Brilliancy in the sample is 80%. An average brilliancy of 50% means
half of the stone returns flash. |
|
Comments |
The comment section is critical because it generally designates the country of origin
of the gemstone as well as specifying what, if any, treatment(s) the gem has been
subjected to. In the sample, the 3.11 is classified as Burma without heat enhancement.
Some gems may receive an Estimated Commercial Acceptability (ECA) comment. (Not
shown in sample.) This is usually used as a split grade. For example, a gemstone
with a 4 color and an ECA of 3.5 is priced as a 3.75 color grade. |
|
Total Quality Integration Rating |
This comment integrates the total visual impact of the gem into a verbal description
and may or may not have an effect on the price of the gem. In the sample it is Excellent.
Look at the Color Rating (AGL). Excellent translates into 1.5. The TQIR can increase
or decrease the final grade only 1/2 of a grade. Therefore, in this sample, a TQIR
of 1.5 raises the 3.5 color grade to a 3. If the TQIR is lower than the color grade,
it means the stone may have a problem, and the TQIR can actually lower the final
grade of the stone 1/2 grade. |
AGL Color Rating Scale
|
1 - 2 |
3 - 4 |
5 - 6 |
7 - 8 |
9 - 10 |
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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 color. For
example, the greener the emerald, the redder the ruby, or the bluer the sapphire,
the lower the numerical grade on an AGL scale. The reason the 3.11 sapphire is a
3.5 in this sample is the fact the stone has 70% blue as its primary color. It is
that simple. The less primary color, the higher the numerical color grade. For example,
a 65% primary color would probably be graded a 4.5 color.
In establishing a base for international quality reference standards, AGL had to
be sure that all stones from the best to the worst could be accommodated by the
system. Therefore, the top of the line has become almost a theoretical standard
of excellence. Please do not ask for 1.00 to 2.00 color grades. Because of the AGL's
stringent grading practices, a 3.5 color is usually the best color grade any gem
will receive. A 3.5 colored stone on an AGL Grading Report is nearly synonymous
with a D-color diamond on a GIA Diamond Grading Report. On occasion, because of
our international contacts, we may find exceptional examples that will receive even
better color grades.
AGL Tone Scale
|
0..5..15..20 |
25..30..35 |
40..45..50 |
55..60..65 |
70..75..80..85 |
90..95..100 |
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Very Light |
Light |
Light-Medium |
Medium |
Medium-Dark |
Dark-Very Dark |
Tone describes the lightness or darkness of a gemstone. Color considered alone without
taking into account the tone will lead to errors in interpretation. If a stone is
too light in tone, the color will not be rich enough. Conversely, if a stone is
too dark, it will sacrifice transparency and brilliancy.
AGL Clarity Scale
|
FI |
LI1...LI2 |
MI1...MI2 |
HI1...HI2 |
E1...E2...E3 |
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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. Here
is a good rule of thumb to remember: You will probably not see inclusions in a Lightly
Included (LI) gem, you may see some inclusions in a Moderately Included (MI) gem,
and you will probably see inclusions in a Heavily Included (HI) gem. Excessively
Included (E) gems have durability problems and should be avoided.
AGL Cutting/Finish Scale
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1 |
2 to 3 |
4 to 6 |
7 to 8 |
9 to 10 |
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Excellent |
Very Good |
Good |
Fair |
Poor |
The cutting of a gemstone numerically describes the overall appearance of a gem.
The finish grade refers to the polish of a gem. These are very difficult numbers
to obtain for a colored gemstone. Unlike diamonds which are cut according to strict
mathematical parameters, most colored gemstones are cut for weight retention.
Ideal Parameters
|
Carat Weight |
1 carat or larger |
|
Color |
Good (6) or better |
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Tone |
Ideal tone for ruby, sapphire and emerald ranges from medium to dark (65-85).
Ideal tone for other gem types varies from light to medium (20-65). |
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Clarity |
Moderately Included Two (MI2) or better |
|
Average Brilliancy |
50% or more |
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Cutting/Finish |
Good (6) or better
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