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 Color |
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 The observer |
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 The eye must be quite relaxed. |
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| The light |
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The light must be equivalent
to that one diffused by a clear sky in North to half day under an average
latitude: emission spectrum continuous richer in radiation blue. |
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Neon tubes are not recommanded (bad),
because the emission lines in blue excite the fluorescence of certain diamonds. Even a
colour temerature of 7,000°K (Kelvin) is also note recommanded. The best lamps must
have a colour temperature of 6,500
Kelvin and meet the CIE standard (International Commission on Illumination). |
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Daylight rich UV light
(sea, mountain) changes the aspect of a diamond. |
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| The stone |
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The stone must be clean
(a dirty girdle obscures diamond and changes its aspect). |
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Be careful with the
stones carrying traces of blue pencil, whose pavilion is coated
(clean these traces before estimating the colour). |
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The stone must not be seted. |
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| Procedure |
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The colour of the stone
can be determined by using a GIA (Gemological Institute of America)
Certified set of master stones and/or
the colorimeter, a
computer which accurately grades the colour of a polished diamond. |
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Observe the diamond on a ultrawhite pre-folded cards,
under  an incidence of approximately 30°
compared to the pavilion, not to be obstructed by fires and the brilliance. |
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The master colour grading diamond is a
non-fluorescent diamond, internally clean (« intelligent » VS2 at
best), of size equivalent to diamonds to be tested, correctly proportioned. |
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If I
have a master colour grading diamond « a » and « b » located like below: |
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 a diamond of
colour equal or higher than « a » is « F » at least. |
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a diamond of
colour equal or higher than « b » is « H » at the maximum. |
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a diamond of
colour ranging between « a » and « b » is « G ». The ideal master colour grading diamonds is located exactly at the limit of two grades.
Example: the stone « X » located at the limit of the grades Exceptional
White (E) and Rare White + (F). |
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| Results |
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Exceptional White +
Exceptional White |
D
E |
Diamond disappears almost in the ultrawhite pre-folded
cards. |
Rare white +
Rare white |
F
G |
A light tint is perceptible on side. |
| White |
H |
A tint is perceptible on side, difficult to see front
view. |
| Slightly Tinted White |
I - J |
A tint is visible front view. |
| Tinted White |
K - L |
Easily visible tint front view. |
| Tinted Colour |
M - Z |
Tint very easily visible front view (speak sometimes
about 1st tinted, 2nd tinted, 3rd tinted,
4th tinted according to the intensity of this colour). |
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| « D » is the best
grade (there is no A, B, or C), and « Z » is the worst grade. |
| A diamond of really tint is a « diamond of
particular colour »: fancy colour. The limit between a tinted stone (Z) and a
stone of particular colour can be evaluated using a master colour grading set. Be careful with diamonds of colour artificially modified by
irradiation and heat treatment (proof brought by the absorption spectra and fluorescence). |
| Diamonds Fancy colour have 5
degrees of different tints: fancy light, fancy, fancy intense, fancy vivid and
fancy deep. If the diamond colour is yellow (there are diamonds in all the colours: blue, red, pink, yellow, etc...). For example: it's a fancy light yellow
diamond or a fancy intense yellow diamond. |
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| A diamond whose colour was modified
artificially, must be mentioned in section « Comments » on the certificate. You will find these
terms « Colour enhanced ». |
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| Colour grading scale |
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| GIA |
Antwerp |
E. O. |
AGS |
CIBJO - IDC |
Scandin. Std. |
| Colourless |
D |
0+ |
95 |
0 |
Exceptional White + |
River |
| E |
0 |
90 |
1 |
Exceptional
White |
| F |
1+ |
85 |
2 |
Rare White + |
Top Wesselton |
Near
Colourless |
G |
1 |
80 |
3 |
Rare White |
| H |
2 |
75 |
4 |
White |
Wesselton |
| I |
3 |
70 |
5 |
Slightly
Tinted White |
Top Crystal |
| J |
4 |
60 |
Crystal |
Faint
Yellow |
K |
5 |
55 |
6 |
Tinted White |
Top Cape |
| L |
6 |
50 |
| M |
7 |
45 |
7 |
Tinted Colour |
Cape |
Very
Light
Yellow |
N |
8 |
40 |
| O |
9 |
35 |
8 |
Light Yellow |
| P |
10 |
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| Q |
11 |
| R |
12 |
9 |
Light
Yellow |
S |
13 |
Yellow |
| T |
14 |
| U |
15 |
| V |
16 |
10 |
| W |
17 |
| X |
18 |
| Y |
19 |
| Z |
20 |
Colour Grading Scales for diamonds
0.46 carat and above
GIA : Gemmological Institute of
America.
Antwerp : Belgium.
E. O. : Extrême-Orient (Far East).
AGS : American Gem Society.
CIBJO : Confédération Internationale de la Bijouterie,
Joaillerie, Orfèverie. International Confederation of Jewelry, Silverware, Diamonds,
Pearls and Stones.
IDC : International Diamond
Council.
Scandin. Std.: Scandinavian Standard. |
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| Fluorescence |
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Fluorescence comes from
a reaction between the energy of the light and the atoms of diamond. In the
majority of the cases, this fluorescence is of blue colour. |
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The degree of
fluorescence is determined by comparing a diamond with a master fluorescence
diamonds grading by exposure to the ultraviolet (UV) rays. If the diamond remains
dark, it is not fluorescent. |
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The fluorescence of
the diamond must be noted like a characteristic on the certificate:
- None or Nil.
- Very slight (blue).
- Slight (blue) or Faint.
- Medium (blue).
- Strong (blue).
- Very strong (blue). |
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A slight fluorescence
depreciates diamonds D, E, and F. A slight fluorescence gives an increase in
value to diamonds equal or below G. |
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1.55 carat E-SI1 |
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0.81 carat D-SI2 |
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1.37 carat F-IF |
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1.57 carat F-VS1 |
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1.72 carat E-VVS1 |
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| Price: £ 9,901 |
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| Price: £ 2,335 |
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| Price: £ 16,904 |
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| Price: £ 10,762 |
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| Price: £ 31,363 |
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