Diamond Education
The AGA-LBI™ and DFS™ System
With the advent of ImaGem®, which is capable of
physically measuring light behavior in diamonds, AGA uses the AGA-Light Behavior
Index (LBI) and AGA-Durability-Finish-Size (DFS) systems. 
The original AGA
Cut Class system was based on a conservative and traditional view of how
diamonds are best cut, but with ImaGem light measuring devices, we are able
to broadly open the field of diamond grading for new cut styles and innovation.
The original AGA Cut Class system will be phased out as we begin to process
fancy shape diamonds. At this time we are only using ImaGem for round and
princess cut diamonds. We use these new systems on the LightStar™ Report,
the DiamondLight™ Index,
the AGA Diamond Grading Report and AGA Diamond Trade Report.
With new technology come changes in how diamonds can be assessed for quality. Both old and new systems are useful, but we believe the AGA-LBI and AGA-DFS systems are better overall in describing diamond light behavior and cut quality.
We introduce you here to the ImaGem terminology for grading Brilliancy, Sparkle and Intensity. Then we present the rules of how this results in our AGA grading of Light, the Light Behavior Index (LBI) in an 8 category scale.
Next we introduce the AGA-DFS system. We use 5 categories, 0 to 4, as this is sufficient to describe the parameters involved.
We report AGA-LBI and the AGA-DFS grade in combination only, at this time.
Brilliancy, Sparkle and Intensity are measured and reported individually
by ImaGem.
The numeric measures used for Brilliancy, Sparkle and Intensity
FOR ROUND DIAMONDS
Brilliancy:
Excellent: 200 to 150;
Very Good: 149.9 to 120;
Good: 119.9 to 110;
Good to Fair: 109.9 to 100;
Fair: 99.9 to 80;
Commercial: 80 to 0.
Sparkle:
Excellent: 120 to 70;
Very Good: 69.9 to 40;
Good: 39.9 to 20;
Good to Fair: 19.9 to 10;
Fair: 9.9 to 5;
Commercial: 5 to 0.
Intensity:
Excellent: 500 to 160;
Very Good: 159.9 to 125;
Good: 124.9 to 115;
Good to Fair: 114.9 to 110;
Fair: 109.9 to 105;
Commercial: 104.9 to 100
FOR PRINCESS CUT DIAMONDS
Brilliancy:
Excellent: 200 to 130;
Very Good: 129.9 to 120;
Good: 119.9 to 110;
Good to Fair: 109.9 to 100;
Fair: 99.9 to 80;
Commercial: 80 to 0.
Sparkle:
Excellent: 120 to 60;
Very Good: 59.9 to 40;
Good: 39.9 to 35;
Good to Fair: 34.9.9 to 20;
Fair: 9.9 to 5;
Commercial: 4.9 to 0.
Intensity:
Excellent: 500 to 140;
Very Good: 139.9 to 120;
Good: 119.9 to 110;
Good to Fair: 109.9 to 105;
Fair: 104.9 to 102;
Commercial: 101.9 to 100
AGA reserves the right to adjust the quality classifications attached to these ImaGem number as required. The numbers above are solid, and not expected to change in the future.
| Brilliancy Sparkle Intensity |
"EX" Excellent |
"VG" Very Good |
"GD" Good |
"GF" Good to Fair |
"FR" Fair |
"CM" Commercial |
|---|---|---|---|---|---|---|
| AGA rules to convert to LBI score. | 1 V. Good allowed 2 Ex required |
1 Good allowed 2 Ex or Very Good required |
1 Fair allowed 1 Good allowed 1 Ex or V. Good required |
2 Fairs allowed 1 Ex to Good required |
3 Fairs | 1 or more graded as Commercial |
| AGA-LBI Overall Grade | Excellent* | Very Good** | Good | Good to Fair | Fair | Commercial |
*Excellent+ is reserved for diamonds that score all three ImaGem measures in the "Excellent " range.
**Very Good+ is reserved for diamonds that score 1 EX and 2 VG, or 3 VG ImaGem measures.
The eight possible grades are: Excellent+, Excellent, Very Good+, Very Good, Good, Good to Fair, Fair and Commercial
AGA Durability-Finish-Size (DFS) standards for use only with direct measurement of Light Behavior technology from ImaGem., Inc.
The AGA-DFS standards.
DFS is scored on a 0 to 4 scale. This system is carefully weighted arithmetically for internal consistency of results. We will supply a software package, which allows you to perform this task on your own computer, but without a VeriGem device to use along with the DFS, I still suggest you use the traditional AGA Cut Class system for more discrimination on cut quality.
0 is Excellent to Very Good.
1 is Very
Good to Good.
2 is “Average”, Good to Fair.
3 is Fair to Commercial
4 is Commercial to Poor.
STEPS #1A. or #1B.
Round diamonds
Total Average Depth %:
55% to 63.0% scores 0 or lower
<55% scores 1 or lower
>63% to 70% scores 1 or lower
>70% scores 2 or lower
Fancy Shaped Diamonds
Total Average Depth %:
50% to 75% scores 0 or lower
<50% scores 1 and lower
>75% to 80% scores 1 or lower
>80% scores 2 or lower
STEP #2
Rounds and Fancy Shapes
Girdle Thickness:
Thin to Slightly Thick score 0 or lower.
Very Thin, Thick or Very Thick score 1 or lower.
Extremely Thin, or Extremely Thick score 2 or lower.
STEP #3
Rounds and Fancy Shapes
Culet Size:
None to Medium score 0 or lower.
Large, or Very Large score 1or lower.
Extremely Large score 2 or lower.
STEPS #4 and #5
Rounds and Fancy Shapes
Finish: The lowest score of Polish or Symmetry controls the
deduction.
Polish and Symmetry
Excellent, Very Good and Good score 0 or lower.
Fair score 1 or lower.
Poor score 2 or lower.
STEP#6
Round diamonds only:
Average Crown angle:
29 degrees or greater score 0 or lower.
26 to 28.9 degrees score 1 or lower.
< 26 degrees score 2 or lower.