Understanding a diamond color grading.
The subject of diamond colors is a extremely deep and complex subject and takes highly skilled and experienced graders to master the complexity of color in a diamond.
How is the color of a diamond determined?
Firstly color can be divided into 3 main categories namely
- Regular colors
- Fancy Colors
- Treated Colors
How are regular colored diamonds graded?
Diamonds have a color grading system that refers to the absence of color rather than color itself. Internationally recognized diamond colors are measured on a scale using the alphabet starting at D which is totally colorless to Z (pale yellow or brown color). D, E and F’s fall into the colorless category while G- J are near colorless. K- M are faint yellows, N-R is very light yellow, S-Z is light yellow and Z+ is used to describe fancy color diamonds. Brown diamonds darker than the K color rage is usually described using their letter grade plus a descriptive phrase, for example, M - Faint Brown (Color Scale +Color description). Diamonds with more depth than the color Z will fall into the fancy color range.
n order to determine a color of a diamond, diamond graders compare a diamond against the set of master stones. Each master stone falls into a very narrow color category.
What is important to note is that every grade of color falls into a different price range.
How are diamonds graded by a diamond grader?
Color grading of diamonds is done in a consistent and controlled environment or lighting box, fitted with daylight equivalent lamps (5500 -6500 degrees Kelvin). The reason for this is that the lower the lights degrees the more likely it will influence the color of a diamond.
|Diamond grading lamps are between 5500-6500 degrees Kelvin|
Accurate color grading can only be performed with unset diamonds. Natural color diamonds is graded from a side view (pavilion side view) unlike fancy colored diamonds that is graded from a top view (table side facing up).
|Normal diamond colors are graded from a side-view|
Why in-house grading is not as accurate as Laboratory color graded diamonds?
A laboratory will possess a complete set of master stones representing every color grade, the independent grader usually works with a smaller subset of master stones that covers only the typical grade range of color they expect to encounter while grading. A common subset of master stones would consist of mainly five diamonds in several increments for example D, H, L, P and Z. All other intermediate grades are estimated by the grader.
|In-House graders only use a sub-set of master stones|
How are Fancy Color Diamonds graded?
Diamonds come in a large variety of colors and any diamond exhibiting a color or
Yellow or brown color diamonds more intense in color than the color "Z” is considered a Fancy Colored Diamond
Fancy Color diamonds are graded using 3 main factors
Hue refers to the diamonds color classification for example; yellow, red, blue, brown etc.
There are 8 primary hues used in the fancy color range
- Pink (http://www.argylepinkdiamonds.com.au/colour-grading)
Although the primary color is used to describe the diamonds hue other colors are often combined with the primary hue to add a more detailed description for example; Yellow – brownish (primary hue + more detailed description). Two or more colors can be used alongside the primary hue. Brown and grey can be added as primary hues but are mostly used in combination with the other hues.
Laboratories use a list of 27 detailed hues to further describe a diamonds color.
- Orangy Pink
- Pinkish orange
- Yellowish Orange
- Green Yellow
- Yellow Green
- Yellowish Green
- Bluish Green
- Blue Green
- Green Blue
- Greenish Blue
- Violetish Blue
- Blueish Violet
- Pinkish Purple
- Pink Purple
- Purple Pink
- Purplish Pink
At times modified color combinations can be added e.g., Brown overtone, Brown-Olive.
2. Diamond Color Saturation
Saturation refers to the intensity of the hue in the diamond and are classified in 9-10 classes. Some might add the Vivid+ while others may not.
- Very Light,
- Fancy Light,
- Fancy Dark,
- Fancy Intense,
- Fancy Deep,
- Fancy Vivid or
Grading Fancy Pink Diamonds
Numbers are also used to describe diamonds saturation. Argyle diamonds in Australia will use the numbers 1-9 to describe the saturation of their Pink Diamonds. The number 9 is used to describe the Faint colors while the 1 is used to describe the vivid colors.
An example of Argyle’s number descriptions for their Pink diamonds would be -
1 P for a Vivid Pink or 1PP for a Vivid Purplish Pink etc.
Other Color terms used to grade the color of a diamond.
It’s not uncommon to find other terms referring to a diamonds color, especially the retail industry one would find "Champagne", "Cognac" and "Coffee" referring to different types of brown diamonds. The term champagne is often used to describe a light yellowish brown color. Cognac for a Orange-Brown diamond and Coffee for a diamond that is a Deep Brown or a Brown Vivid+ color diamond.
Some grading agencies may also describe brown stones as using the term “Fancy” in front of the description for example Fancy Yellowish-Brown, Fancy Light Brown, Fancy Intense Brown etc.
The tone of a diamond refers to the lightness or darkness of the primary hue.
How are diamonds Color treated?
Generally there are four major methods to artificially alter the color of a diamond: irradiation with high-energy subatomic particles; the application of thin films or coatings; and the combined application of high pressure and high temperature (HPHT). However, there is recent evidence that fracture filling is not only used to improve clarity, but can be effective in enhancing a diamonds color.
Irradiation and coatings only modify color (as some irradiation methods only produce a thin "skin" of color), and are usually only they are applied to polished diamonds but have been found on rough diamonds as well. HPHT treatment is used to modify and remove color from either rough or cut diamonds however not all diamonds are suitable for HTHP treatment. Irradiation and HPHT treatments are usually permanent. Pressures of up to 70,000 atmospheres and temperatures of up to 2,000 °C (3,632 °F) are used in HPHT procedure.
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