Diamond color

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Sep 09, 2010 - 06:44 am

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Diamond Color

	The observer
	The light
	The stone
	Procedure
	Results
	Color grading scale
	Fluorescence

The observer

The eye must be quite relaxed.

The light

	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.
	Neon tubes are not recommanded (bad), because the emission lines in blue excite the fluorescence of certain diamonds. Even a color temerature of 7,000°K (Kelvin) is also note recommanded. The best lamps must have a color temperature of 6,500 Kelvin and meet the CIE standard (International Commission on Illumination).
	Daylight rich UV light (sea, mountain) changes the aspect of a diamond.

The stone

	The stone must be clean (a dirty girdle obscures diamond and changes its aspect).
	Be careful with the stones carrying traces of blue pencil, whose pavilion is coated (clean these traces before estimating the color).
	The stone must not be seted.

Procedure

The color 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 color of a polished diamond.

Observe the diamond on a ultrawhite pre-folded cards, under Diamond color observation

an incidence of approximately 30° compared to the pavilion, not to be obstructed by fires and the brilliance.

The master color grading diamond is a non-fluorescent diamond, internally clean (« intelligent » VS2 at best), of size equivalent to diamonds to be tested, correctly proportioned.

	If I have a master color grading diamond « a » and « b » located like below:
		a diamond of color equal or higher than « a » is « F » at least.
		a diamond of color equal or higher than « b » is « H » at the maximum.
		a diamond of color ranging between « a » and « b » is « G ». The ideal master color 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).

Results

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 Color	M - Z	Tint very easily visible front view (speak sometimes about 1^st tinted, 2^nd tinted, 3^rd tinted, 4^th tinted according to the intensity of this colour).

« 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 color »: fancy color. The limit between a tinted stone (Z) and a stone of particular color can be evaluated using a master color grading set. Be careful with diamonds of color artificially modified by irradiation and heat treatment (proof brought by the absorption spectra and fluorescence).

Diamonds Fancy color have 5 degrees of different tints: fancy light, fancy, fancy intense, fancy vivid and fancy deep. If the diamond color is yellow (there are diamonds in all the colors: blue, red, pink, yellow, etc...). For example: it's a fancy light yellow diamond or a fancy intense yellow diamond.

A diamond whose color was modified artificially, must be mentioned in section « Comments » on the certificate. You will find these terms « Color enhanced ».

Color grading scale

GIA		Antwerp	E. O.	AGS	CIBJO - IDC	Scandin. Std.
Colorless	D	0+	95	0	Exceptional White +	River
	E	0	90	1	Exceptional White	River
	F	1+	85	2	Rare White +	Top Wesselton
Near Colorless	G	1	80	3	Rare White	Top Wesselton
	H	2	75	4	White	Wesselton
	I	3	70	5	Slightly Tinted White	Top Crystal
	J	4	60	5	Slightly Tinted White	Crystal
Faint Yellow	K	5	55	6	Tinted White	Top Cape
	L	6	50	6	Tinted White	Top Cape
	M	7	45	7	Tinted Color	Cape
Very Light Yellow	N	8	40	7		Cape
	O	9	35	8		Light Yellow
	P	10
	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
Color 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.

Fluorescence

	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 color.
	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.
	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).
	A slight fluorescence depreciates diamonds D, E, and F. A slight fluorescence gives an increase in value to diamonds equal or below G.