The determination of color in an HRD laboratory is carried out on the basis of visual comparisons, with use of a series of calibrated master stones which, like the CIBJO master stones, are based on the color comparison stones assembled in 1977 by representatives of the International Diamond Manufacturers Association (IDMA), The World Federation of Diamond Bourses (WFDB), and CIBJO.
For color grading, fluorescent tube lamps are used at CIE (Commission International d'Eclairage) light temperature 065. The color grading of a diamond is confirmed only after four independent identical assessments have been obtained.
The fluorescence of a diamond is examined in long-wave UV light (366 nm), compared with the fluorescence of calibrated stones, and described as follows:
nil - slight - medium - strong.
The color comparison to masters tones is done under normalized artificial light, equivalent to Northern Daylight (IR May 78).
It is recommended that the characteristics of the artificial light source to be used, approximate the C.I.E.-standard illuminant 065 (C.I.E .. = Commission International d'Eclairage (International Commission of Illumination)).
International color Grading Scale according to IDC:
|
|
International color Grading Scale |
|
GIA |
|
exceptional white + |
blanc exceptionnel + |
hochfeines WeiB + |
0 |
|
exceptional white |
blanc exceptionnel |
hochfeines WeiB |
E |
|
rare ~hite + |
blanc extra + |
feines WeiB + |
F |
|
rare white |
blanc extra |
feines WeiB |
G |
|
white |
blanc |
WeiB |
H |
|
|
|
. |
|
|
slightly tinted white |
blanc nuance. |
leicht get6ntes WeiB |
I |
|
|
|
|
J |
|
tinted white |
legerement teints |
getbntes WeiB |
K |
|
|
|
|
L |
|
tintedcolor 1 |
couleur teintee 1 |
get6nt 1 |
M |
|
|
|
|
N |
|
tinted color 2 |
couleur teintee 2 |
get6nt 2 |
0 |
|
|
|
|
P |
|
tinted color 3 |
couleur teintee 3 |
get6nt 3 |
Q |
|
|
|
|
R |
|
tinted color 4 |
couleur teintee 4 |
get6nt 4 |
S-Z |
| CIBJO color Table 1986 | Scan. D. N. |