After discussing general diamond grading (white/colorless diamonds) in the earlier post of Insights into Diamonds series, now is the time to have a deeper look into different colors and types of diamonds.
Diamond in normal range are colorless through light yellow. Fancy color diamonds are yellow and brown diamonds that show color beyond Z color or exhibiting any other color face-up. Such rare stones come in almost every color of spectrum but most importantly in blue, pink, green and red. As discussed in diamond grading article, diamonds in range of D-Z showing decrease in value by exhibiting color and the exact opposite happens for fancy color diamonds, their value increase by the strength and purity of color.
Pink Diamond: appearance of pink color in diamonds is a result of enormous pressure that leads to structural damage to the crystal lattice of the diamond after it has begun to grow. This distortion in the crystal structure cause internal graining which results in pink color zones to appear.
In fancy color diamonds, Color outweighs all other Cs (clarity, cut and carat) in determining the value. Color has three attributes that help grading it properly: hue (the appearance of red, blue, green, or anything in between), tone (the relative lightness or darkness of a color), and saturation (the relative strength or weakness of a color). The color
appearance of a diamond is the result of a combination of these three attributes.
Blue Diamond: Color of blue in diamonds is result of presence of Boron during formation. Boron is mostly available in larger quantities closer to the earth surface, therefore its presence in earth mantle where diamonds are formed is extremely rare, and that is why blue diamonds are so scarce.
The GIA color grading system uses nine grades to distinguish color ranges. These are: Fancy Vivid, Fancy Intense, Fancy Deep, Fancy Dark, Fancy, Fancy Light, Light, Very Light and Faint. For fancy colored diamonds, the general rule of thumb is that the stronger the hue, the more valuable the stone becomes.
Yellow Diamond: Yellow in diamonds is caused by presence of nitrogen within the stone that filters blue/violet range of visible light spectrum and reflects yellow. Nitrogen is abundant in earth crust, it can often find a way into diamond during formation process.
Diamond types: pure carbon is the essential composition of diamonds. Many diamonds certain trace elements such as nitrogen or boron, acquired naturally during the formation. Availability of such trace elements and other imperfections are important because they cause the color and ultraviolet fluorescence reactions in diamond. The presence or absence of these lattice defects can affect a diamond’s appearance. Initially diamonds were divided in two types: Type I diamonds contain nitrogen and Type II diamonds show pure absence of nitrogen.
These diamonds contain nitrogen atoms in clusters. Approximately 95% of natural diamonds are type Ia. They normally vary from near-colorless to light yellow. These so-called “cape” diamonds derived their name from diamonds that were initially mined in or near Cape Province, South Africa.
These diamonds also contain nitrogen, but as isolated atoms instead of clusters. They are often bright yellow in color, and are extremely rare. The trade sometimes refers to these colors as “canary.”
These diamonds have no measurable nitrogen or boron impurities; they are usually colorless but they can also be gray, light brown, light yellow or light pink. Among all diamonds, those that are type IIa are chemically the most pure.
These diamonds are known to conduct electricity. The trace element boron is responsible for most diamonds that are blue or grayish blue in color.
Some of the 27 hue names include modifiers such as purplish or yellowish. A modifier in a hue name does not denote a lack of potential strength, or purity, to the color. Light or dark colors at low levels of saturation are challenging to discern. Thus, fewer terms are used in these areas (as evident in the hue circles for lighter and darker tone). These terms may be modified in one of two ways. The first is the use of the word pink as a substitute for red in the medium to light tones and moderate to weakly saturated versions of reddish purple, red-purple, purple-red, purplish red, red, orangy red, and reddish orange. The other is the addition of brown/brownish or gray/grayish to the description. As colors transition darker or weaker, they appear more brown or gray. Warm hues (such as yellow, orange, or red) appear browner as they darken or weaken; cool colors (such as blue or green) appear grayer. In each instance, the fancy grades and color descriptions represent a range of color sensations, not a “single” color sensation.
Green Diamond:Green color is caused by exposure to radiation, this natural phenomenon occurs when diamonds come in close contact with radioactive uranium from rocks near earth surface. In rare cases radiation can be found in groundwater sources. Research shows green diamonds are more common in alluvial deposits because diamonds transported to sources of radiation which is more likely than for radiation to exist near a kimberlite source of diamond.
In fancy color diamonds, clarity is not a determining factor in value. Even diamonds with many inclusions that result in a low clarity grade are sought after by collectors as long as they display an attractive color face-up. Inclusions that can threaten the durability of diamond would lower the value significantly.
Size and shape are two aspects that can influence the color, larger diamonds usually have deeper pavilion that facilitates the farther light can travel in it. This can often lead to a richer, more intense color. The style of cut can also play a key factor in color. Usually mixed cuts like the radiant cut can intensify the color in diamonds and radiant cut provides (including majority of fancy cuts) provides higher yield from the rough than a standard round brilliant.
For more information on fancy color diamonds, download GIA Colored Diamonds Color Reference chart booklet.