CUT GRADE
Proportions | Polish | Symmetry
2022
2 | Cut Grade -
HRD ANTWERP CUT GRADE
Denition of Cut Grade
The description of the Cut Grade on a grading report is subdivided into 3 grades: proportions, polish and symmetry.
Each grade is divided into 4 categories: Excellent, Very Good, Good and Fair.
• The proportions are determinative for the brilliancy and the re of the diamond.
• The polish describes the nish of the facets
• The symmetry describes the variations of the dierent parameters which dene the proportions.
HRD Antwerp Cut Grade
Proportions Polish Symmetry
Excellent Excellent Excellent
Very Good Very Good Very Good
Good Good Good
Fair Fair Fair
Cut Grade | 3
HRD ANTWERP CUT GRADE
Proportions
Determination of proportions
For a diamond to show an optimal combination of brilliancy and re, it has to be polished with due attention
to the angles of inclination and proportional relations between the various parts of the stone. If the angles
and proportions are not optimal, this can lead to the appearance of one or more specic eects in the stone,
which are detrimental to its beauty. When grading the proportions of a polished diamond, the main issue is
therefore to evaluate if, and if so to what extent, these eects occur.
Parameters that can characterize the proportions for the round
brilliant
• The crown angle (β)
• The pavilion angle (α)
• The proportion of the table width to the diameter (% t)
• The proportion of the crown height to the diameter (% hc)
• The proportion of the pavilion depth to the diameter (% hp)
• The proportion of the girdle thickness to the diameter (% a)
• The culet size (% culet)
• The proportion of the total depth to the diameter (% td)
• The sum of the crown- and pavilion angle (α+β)
• The half length of the upper girdle facets
• The half length of the lower girdle facets
• The fish eye effect
• The effect culet visible in the bezels
Profile of a diamond and the different parameters
% TOTAL DEPTH
% PAVILION DEPTH
% CROWN HEIGHT
% TABLE WIDTH
AV. DIAMETER = 100 %
% GIRDLE
CROWN ANGLE
PAVILION ANGLE
SUM
α & β
% LENGTH HALVES PAVILION
% LENGTH HALVES CROWN
% CULET
4 | Cut Grade
HRD ANTWERP CUT GRADE
Proportions
Overview of the different parameters per category
If the measurement results are classied in two dierent categories, the lowest proportion grade is considered
to be the overall reading.
Effects that can be perceived when observing the stone perpen-
dicular to the table
• Fish Eye: The reection of the girdle is partially or completely visible in the table
(small pavilion angle and a large table width).
• Culet visible in the bezels: The diamond shows an abnormal amount of scintillation, due to the culet
and the surrounding facets being visible through the bezels (a large total
depth and crown angle).
Fair Good Very Good Excellent Very Good Good Fair
Crown angle (β) up to 25.9° 26.0 to 27.9°
28.0 to 31.2°
31.3 to 36.7° 36.8 to 38.2°
38.3 to 40.0°
40.1° and up
Pavilion angle (α) up to 38.4° 38.5 to 39.5° 39.6 to 40.5° 40.6 to 41.8° 41.9 to 42.1° 42.2 to 43.1° 43.2° and up
Table width
up to 47 %
48 to 49 %
50 to 51 %
52 to 62 %
63 to 66 % 67 to 70 % 71 % and up
Crown height up to 8.5 % 9.0 to 10.5 % 11.0 to 11.5 %
12.0 to 17.0 % 17.5 to 18.0 %
18.5 to 19.5 % 20.0 % and up
Pavilion depth up to 39.5 % 40.0 to 41.0 % 41.5 to 42.5 % 43.0 to 44.5 % 45.0 % 45.5 to 46.5 % 47.0 % and up
Girdle up to 0.5 % 1.0 to 1.5 % 2.0 % 2.5 to 4.5 % 5.0 to 5.5 % 6.0 to 7.5 % 8.0 % and up
Culet size 0.0 to 0.9 % 1.0 to 1.9 % 2.0 to 3.9 % 4.0 % and up
Total depth up to 52.9 % 53.0 to 55.4 % 55.5 to 58.4 % 58.5 to 63.5 % 63.6 to 64.4 % 64.5 to 66.9 % 67.0 % and up
Sum α and β up to 67.9° 68.0 to 69.9° 70.0 to 72.4°
72.5 to 77.7° 77.8 to 79.4°
79.5 to 80.4° 80.5° and up
Half crown
up to 25 % 30 % 35 to 55 %
60 % 65 % 70 % and up
Half pavilion
up to 55 % 60 %
70 to 85 % 90 % 95 % and up
Fish-eye eect Excellent Good Fair
Culet in bezels Excellent Good Fair
65 %
Cut Grade | 5
HRD ANTWERP CUT GRADE
Proportions
Description of the girdle and influence on the proportions
The influence of the culet size on the proportions
Description of the girdle Measured value Proportion Grade
Extremely thin 0.0 – 0.5 % Fair
Very thin 1.0 – 1.5 % Good
Thin
2.0 % Very Good
2.5 %
Excellent
Medium
3.0 – 4.5 %
5.0 %
Very Good
Thick
5.5 %
6.0 %
Good
Very thick 6.5 – 7.5 %
Extremely thick 8.0 % and up Fair
Description of the culet Culet Size Proportion Grade
Pointed 0.0 % (< 0.033 mm) Excellent
0.1 % (0.033 mm) – 0.9 %
1.0 – 1.9 % Very Good
2.0 – 3.9 % Good
Large 4.0 % and up Fair
6 | Cut Grade
HRD ANTWERP CUT GRADE
Polish
Polish denes all external characteristics of the diamond. These characteristics are mostly the result of
polishing the diamond.
The characteristics being graded
• Scratches
• Percussion gures
• Beard
• Polishing lines
• Abraded facet edges
• Pit
• Burn marks
• Laser marks
Description of the polish
Polish Observation with loupe 10x
Excellent Characteristics, not or very dicult to nd with a loupe 10x
Very Good Characteristics, dicult to nd with a loupe 10x
Good Characteristics, easy to nd with a loupe 10x
Fair Characteristics, very easy to nd with a loupe 10x
Cut Grade | 7
HRD ANTWERP CUT GRADE
Symmetry
Information about the effects
Single Cut effect: The diamond looks as if it has less facets than are really present. A single cut eect is caused
by the angles of the bezels / pavilions and the halves of the bezels / pavilions side.
Bow tie effect: Through the crown side, two dark zones in the shape of a bow tie can be seen.
Not measurable deviations
Measurable deviations
Determination of symmetry
The symmetry describes the variations of the dierent parameters which dene the proportions.
Symmetry-deviations Excellent Very Good Good Fair
Unroundness < 1.0 % < 2.0 % < 4.0 % 4.0 % and up
Variation in crown height < 1.0 % < 2.0 % < 5.0 % 5.0 % and up
Variation in pavilion depth < 2.0 % < 3.0 % < 6.0 % 6.0 % and up
Table out of centre < 1.0 % < 2.0 % < 5.0 % 5.0 % and up
Culet out of centre < 1.0 % < 2.0 % < 5.0 % 5.0 % and up
Table and culet out of centre < 1.0 % < 2.0 % < 5.0 % 5.0 % and up
Variation on the table width < 2.0 % < 4.0 % < 8.0 % 8.0 % and up
Single cut eect < 0.8 % < 2.0 % < 4.0 % 4.0 % and up
Deviation on the crown angles < 2.0° < 4.0° < 8.0° 8.0° and up
Deviation on the pavilion angles < 1.0° < 2.0° < 4.0° 4.0° and up
Deviation on the angles of the lower girdle facets < 1.0° < 2.0° < 4.0° 4.0° and up
Visual
deviations
Deviation of the bezels
Deviation of the pavilions
Cone-shaped girdle
Misalignment
Girdle partly faceted
Bow tie eect
Deviation on the girdle thickness (on max & min)
Deviation on the angles of the upper girdle facets
Naturals
Extra facets
8 | Cut Grade
HRD ANTWERP CUT GRADE
Symmetry deviations
1. Girdle outline not
circular
15. Crown side not aligned
to pavilion side
2. Slanting table 16. Cone-shaped girdle
3. Sloping girdle 17. Girdle partly faceted
4. Culet out of centre
20. Pavilion facets not
symmetrical
5. Table out of centre
22. Pavilion facets not
pointing up
6. Table and culet out
of centre in opposite
direction
23. Deviation on the bezel
angles
7. Table and/or star
facets not symmetrical
24. Deviation on the
pavilion angles
10. Bezels not symmetrical
25. Deviation on the angles
of the upper girdle
facets
12. Crown facets not
pointing up
26. Deviation on the angles
of the lower girdle
facets
13. Varying girdle
thickness
27 Bow-tie
14. Single cut effect (due
to alternating girdle
thickness)
28 Naturals
Extra facets
Cut Grade | 9
HRD ANTWERP CUT GRADE
Symmetry deviations
Different symmetry deviations of the girdle
Perfect symmetry
variation girdle height (B & H) =
max (B&H) – min (B&H) = 2.5 – 2.5 = 0%
variation girdle height (V) =
max (V) – min (V) = 1 – 1 = 0%
variation girdle height = max [variation girdle height (B & H) & variation girdle height (V)] = 0%
single cut = average (H) – average (B) = 2.5 – 2.5 = 0% (<0.8%) => Exc
Single cut effect
variation girdle height (B & H) =
max (B&H) – min (B&H) = 2.7 – 2.3 = 0.4%
variation girdle height (V) =
max (V) – min (V) = 1 – 1 = 0%
variation girdle height = max [variation girdle height (B & H) & variation girdle height (V)] = 0.4%
single cut = average (H) – average (B) = 2.7 – 2.3 = 0.4% (<0.8%) => Exc
Variation girdle height
variation girdle height (B & H) =
max (B&H) – min (B&H) = 3.4 – 2.5 = 0.9%
variation girdle height (V) =
max (V) – min (V) = 1.5 – 1.5 = 0%
variation girdle height = max [variation girdle height (B & H) & variation girdle height (V)] = 0.9%
single cut = average (H) – average (B) = 2.6 – 2.5 = 0.1% (<0.8%) => Exc
Variation girdle height
variation girdle height (B & H) =
max (B&H) – min (B&H) = 3 – 2 = 1%
variation girdle height (V) =
max (V) – min (V) = 1.5 – 0.5 = 1%
variation girdle height = max [variation girdle height (B & H) & variation girdle height (V)] = 1%
single cut = average (H) – average (B) = 2.5 – 2.5 = 0% (<0.8%) => Exc
1% (Valley)
2.5% (Halves)
2.5% (Bezels)
1% (Valley)
2.7% (Halves)
2.3% (Bezels)
2.5%
1.5%
2.5%
3.4%
Vmin = 0.5%
Vmax = 1.5%
Bmin = 2%
Bmax = 3%
Hmin = 2%
Hmax = 3%
2.5%
1%
2.5%
average (H) =
2.5%
average (B) =
2.5%
average (H) =
2.7%
average (B) =
2.3%
average (H) =
2.6%
average (B) =
2.5%
average (H) =
2.5%
average (B) =
2.5%
Illustrations: WTOCD
10 | Cut Grade
HRD ANTWERP CUT GRADE
Conclusion
The proportion grade is based on the average of the measured values. If there is a large deviation on one or
more values, the beauty of the diamond can be inuenced. The table below shows the inuence of symmetry
and/or polish on the nal proportion grade.
Pol. / Sym.
Proportions
Excellent Very Good Good Fair
Excellent Excellent Excellent Very Good Good
Very Good Very Good Very Good Very Good Good
Good Good Good Good Good
Fair Fair Fair Fair Fair
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