ROUND BRILLIANT PROPORTIONS

Final cut quality evaluation

There is no universal approach to derive the price of a diamond based on the combination of its angles, proportions, and symmetry and polish features. There are tables which allow the identification of a diamond within one or another quality group (class).
GIA cut classification
Criteria
 1 2
3
4
Table diameter 53-60% 52-53%

61-64%
51-52%

65-70%
<51%
>70%
Crown angle 34° -35°   32° -34 °

35° -36°

30° -32°

36° -37°
<30°
>37°
Pavilion depth 43% 42% èëè 44%
41-42%
45-46%
<41%
>46%
Girdle thickness Medium Thin
Very thin
Extremely thin
Slightly thick Thick
Very thick
Extremely thick
Culet None - Medium Slightly large
Large
Very large
Finish E-VG G
F
P
Correlation between total height and girdle thickness

Correlation between table diameter, crown height and crown angle

Correlation between table diameter, pavilion height and pavilion angle

HRD proportion classification
Criteria Unusual Good Very good Good Unusual
Crown angle up to 26.9î 27.0î - 30.6î 30.7î – 37.7î 37.8î – 40.6î 40.7 î and more
Pavilion angle up to 38.4î 38.5î – 39.5î 39.6î – 42.2î 42.3î – 43.1î > 43.2î and more
Table diameter,% 71 and more 70 – 67 66 – 53 52 – 51 50 and less
Crown height,% up to 8.5 9 – 10.5 11 – 16 16.5 – 18 18.5 and more
Girdle Extremely thin Very thin Medium and thick Thick and very thick Extremely thick
Pavilion depth,% up to 39.5 40 – 41 41.5 – 45 45.5 – 46.5 47 and more
Culet - - Pointed - 1.9 % 2 % - 3.9 % 4 % and more
Total height,% up to 52.9 53.0 – 55.4 55.5 – 63.9 64.0 – 66.9 67.0 and more
Correlation between total height and girdle thickness


Correlation between table diameter, crown height and crown angle

Correlation between table diameter, pavilion height and pavilion angle

The influence of the cut quality on diamond price
( (From: Verena Pagel- Theisen. "Diamond Grading ABC").
Proportions
Tolerances

Very good

Good

Medium

Poor

Girdle diameter 100% No deviations from tolerances Slight deviations from tolerances up to a maximum of 5 % of values given Strong deviations from tolerances up to a maximum of 10 % of values given Striking deviations from tolerances, more than 10% of values given
Table size 55-66%
Total height including girdle 54-66%
Crown height 11-16%
Pavilion depth 42-45%
Girdle thickness Less than 3% Thin

Medium

Thick Very thick
Reduction in value

none

2-8 %

9-15%

16-25%, over 25% to be recut
Symmetry features (by 10x magnification)
 

Very good

Good

Medium

Poor

Deviation from circular shape

Tilted/eccentric culet

Table unequal exentric culet

 up to 2 % 2-3 % 3-4 % more than 4 %
Symmetry of table edges

Symmetry of facets to each other

Size of facets

Crown 50 : 50

Pavilion 80 : 20

Crown : Pavilion on girdle

Edge displacement

Truncated or short facets crown and pavilion

No symmetry features, or ones only seen with difficulty A few symmetry features not too difficult to see Several symmetry features not too difficult to see or easily seen Large and/or many small symmetry features, easily visible
Size of culet Very small None or small Medium to large Very large/damaged
Symmetry of girdle Even Knife-edged in 1 -2 places or slightly wavy Knife-edged in several places, irregular in several places, and wavy Almost entirely knife-edged, very irregular/of very uneven thickness and wavy
Comprehensive evaluatic Best symmetry, outstanding brilliance Slightly distorted symmetry, good to slightly reduced brilliance Distorted symmetry, slightly reduced to reduced brilliance Strongly distorted symmetry, considerably reduced
Reduction in value None Up to 4 % 5-8 % 9-12 %, over 12 % to be re-cut
External features (by 10 x magnification)
  Very good Good Medium Poor
Girdle Bruted, polished, faceted, very thin and thin Minor rough places, minor fringes Several rough places, several fringes Entirely rough, many fringes
Naturals and extra facets 1-4 beneath the girdle, not wider than the girdle 1 -4 beneath the girdle, about twice as wide as girdle, or very small ones 1 -4 fairly large beneath the girdle, or small ones above the girdle 1-4 larger than 1/4 of the pavilion facets or larger ones above the girdle
Twinning lines,Growth lines, nicks, fractures, Indentation marks None, or very small features Very small to small features Larger features Many and/or large features
Cutting traces, polishing marks, scratches, knots, burn marks None or difficult to see.

No reduction of brilliance

 Difficult to see, to not so difficult to see, Very slightly reduced brilliance Easy to see, slightly reduced to reduced brilliance Immediately visible, obviously reduced brilliance
Comprehensive evaluation None or only very small external features A few small external features A few fairly large external features Many and/or large external features
Reduction in value None Up to 6% 7-10 % 11-15%, over 15 % to be re-cut

It should be noted that price lists do not usually contain precise premium or deduction values for particular cut groups. That is why cut is the most speculative and most difficult "Ñ"of the four.