Color
What is color?
The color of the stone is one of the "4Cs" characteristics, allowing the price of a diamond to be determined based on its classification. This differs between white or colorless diamonds and colored diamonds. Indeed, while white diamonds are graded on a hue scale ranging from bright white to pale yellow, colored diamonds, which are much rarer than colorless ones (5% of diamonds), are classified based on their intensity.
What are the gradations of white or colorless diamonds?
The international standard for white gradations ranging from colorless to a slight tint is that of the "Gemological Institute of America" (GIA).
The assessment of color, rated from D to Z, is crucial in determining the value of the diamond because the whiter the diamond, the more valuable it is. The GIA classifies diamond colors according to the letters: D for pure white to Z for a well-defined yellow.
How to determine the color of a diamond?
To appreciate the color of a diamond, it should be placed in a fold of white bristol and observed from the pavilion and profile to avoid being disturbed by the fire of the facets. This observation with the naked eye is also done under very bright light.
This observation is accompanied by a comparison since, to determine the hue of a diamond, the evaluator uses so-called "master stones" as reference stones from which they compare the diamond being studied to determine its color.
These reference samples must also adhere to certain carats because the larger the diamond, the more intense its color. That is why, for stones up to 1.50 ct, the sample must weigh at least 0.25 ct, while for larger diamonds, it must weigh between 0.50 and 0.75 ct minimum.
What is the treatment for the shade?
It is possible to artificially change the color of a diamond so that brownish to yellowish diamonds obtain a more "white" hue.
This method, known as "HPHT" or High Pressure, High Temperature, involves correcting an error in the diamond's crystallographic structure (which is the cause of the more intense color) and requires subjecting the stone to conditions similar to those of its formation to perfect its structure. The gems are thus heated to over 1500°C and under a pressure of more than 50,000 ATM.
This treatment is permanent and can only be detected in advanced laboratories using analyses in the infrared and ultraviolet spectrum.
It is mandatory to notify this treatment, whether orally or in writing. As a result, this process falls into the "Color enhanced" category of gemological certificates. The diamond consequently loses value because it is artificially treated.
What are colored diamonds?
The natural color
Colored diamonds, also known as fancy color diamonds, are rarer than white diamonds and result from the presence of gases during the crystallization of the gem. The color varies depending on the type of gas to which the carbon atoms were exposed: for example, the presence of nitrogen will give a yellow diamond, while the presence of boron will highlight the blue color.
Colored diamonds have their own classification according to their chromatic intensity. Therefore, the "Fancy Color" of a diamond, that is, its hue, is assessed according to its intensity: the more intense the color, the higher the value of the diamond. The term "Fancy" starts after "Z," with a hint of color being accepted for the scale of White diamonds: Fancy light (very light intensity)
• Fancy (lightly intense) • Fancy intense (slightly intense) • Fancy Vivid (intense) • Fancy Deep (very intense) • Fancy Dark (very very intense)
Moreover, the most sought-after colors on the market are as follows: hydrangea pink, lemon or canary yellow, blue, water green, violet, red, and orange. Conversely, gray, brown, and black are less appreciated and their value remains very accessible.
Color treatment
It is possible to artificially change the color of a diamond through irradiation and heating. However, this transformation of the diamond remains imprecise: the color depends on the original hue of the crystal and one can never be certain of the result. Moreover, the color treatment results in stones that will be of lower quality than a naturally colored gem. This treatment is permanent.
Just like for the modification of the color of a white diamond, it is impossible to determine if a treatment has taken place without the intervention of a laboratory. It is mandatory to notify this treatment, whether orally or in writing. As a result, this process falls into the "Color enhanced" category of diamond gemological certificates. The latter then loses between 60 to 80% of its value.
What is the phenomenon of fluorescence?
Fluorescence is a luminous effect exhibited by certain diamonds when they are exposed to ultraviolet light: they then emit visible light, usually blue (in 95% of cases), but also violet, orange, or red for rare gems.
This fluorescence must be quantified using fluorescence standards and indicated in the certificates according to the following gradation:
• None or Nil: none • Very slight: very light • Slight or Faint: Light • Medium: Medium • Strong: Strong • Very strong: very strong
For fluorescence from Medium to Very Strong, the diamond may (not always) have a slightly "milky white" hue. Indeed, if fluorescence is not directly related to the color of a diamond, it can, however, influence its price and transparency, even though this latter influence remains disputed by experts.
