Color
The colour of a stone is one of the "4 Cs" used to determine a diamond's price based on its classification. This classification differs between white or colourless diamonds and fancy-coloured diamonds. While white diamonds are graded on a scale of hues ranging from brilliant white to pale yellow, fancy-coloured diamonds, which are much rarer than colourless ones (5% of all diamonds), are classified according to their intensity.
What are the gradations for white or colourless diamonds?
The international reference for white gradations, ranging from colourless to a slight hint of colour, is the
"Gemmological Institute of America" (GIA).
The colour assessment, denoted by a letter from D to Z, is crucial to a diamond's value because the whiter the diamond, the more valuable it is. The GIA classifies diamond colours using letters: D for pure white to Z for a pronounced yellow.
How to determine a diamond's color?
To assess a diamond's color, place it in a fold of white Bristol board and observe it through the pavilion and from the side, to avoid being distracted by the fire of the facets. This observation is done with the naked eye under very white light.
This observation is accompanied by a comparison, as to determine a diamond's hue, the appraiser uses "master stones" against which they compare the diamond being studied to determine its color.
These master stones must also meet certain carat requirements because the larger the diamond, the more intense its color. This is why for stones up to 1.50 ct, the master stone must weigh at least 0.25 ct, while for larger diamonds, it must weigh between 0.50 and 0.75 ct minimum.
What is color treatment?
It is possible to artificially change a diamond's color so that brownish to yellowish diamonds achieve a "whiter" hue.
This method, called "HPHT" or High Pressure, High Temperature, consists of correcting an error in the diamond's crystallographic structure (which causes the more intense color) and involves 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 infrared and ultraviolet spectrum analysis.
It is mandatory to disclose this treatment, whether verbally or in writing. As a result, this process falls under the "Color enhanced" category in gemological certificates. The diamond thus loses value because it is artificially treated.
What are fancy colored diamonds?
Natural Color
Fancy colored diamonds, also known as natural colored diamonds, are rarer than white diamonds and result from the presence of gas during the gem's crystallization. The color varies depending on the type of gas the carbon atoms were exposed to: for example, the presence of nitrogen will give a yellow diamond, while the presence of boron will bring out the blue color.
Fancy colored diamonds have their own classification according to their chromatic intensity. Therefore, a diamond's "Fancy Color," meaning its hue, is estimated according to its intensity: the more intense the color, the higher the diamond's value. The "Fancy" designation begins after "Z," a hint of color being accepted for the white diamond scale:Fancy light (very slightly intense)
• Fancy (slightly intense)
• Fancy intense (moderately intense)
• Fancy Vivid (intense)
• Fancy Deep (very intense)
• Fancy Dark (extremely intense)
Furthermore, the most sought-after colors on the market are: hydrangea pink, lemon or canary yellow, blue, aquamarine, 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 modify a diamond's color through irradiation and heating. However, this transformation of the diamond remains imprecise: the color depends on the crystal's original hue, and there is never certainty about the result. Moreover, color treatment results in stones that will be of lower quality than naturally colored gems. This treatment is permanent.
As with modifying the hue of a white diamond, it is impossible to determine if a treatment has occurred without laboratory intervention. It is mandatory to disclose this treatment, whether verbally or in writing. As a result, this process falls under the "Color enhanced" category in 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 some diamonds when 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 certificates according to the following grading:
• None or Nil: none
• Very slight: very slight
• Slight or Faint: slight
• 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, while fluorescence is not directly linked to a diamond's color, it can nevertheless affect its price and transparency, even if this latter influence remains disputed by experts.