A chemically pure and structurally perfect diamond is perfectly transparent with no hue,
or color. However, in reality almost no gem-sized natural diamonds are absolutely perfect. The
color of a diamond may be affected by chemical impurities and/or structural defects in the
crystal lattice. Depending on the hue and intensity of a diamond's coloration, a diamond's
color can either detract from or enhance its value. For example, most white diamonds are
discounted in price when more yellow hue is detectable, while intense pink or blue diamonds
can be dramatically more valuable. Out of all colored diamonds, red diamonds are the
rarest. The Aurora Pyramid of Hope displays a spectacular array of naturally colored diamonds,
including red diamonds.
Possible colors
Diamonds occur in a variety of colors — steel gray, white, blue, yellow, orange, red, green,
pink to purple, brown, and black. Colored diamonds contain interstitial impurities or
structural defects that cause the coloration, whilst pure diamonds are perfectly transparent
and colorless. Diamonds are scientifically classed into two main types and several subtypes,
according to the nature of impurities present and how these impurities affect light absorption:
Type I diamonds have nitrogen atoms as the main impurity, commonly at a concentration
of 0.1%. If the nitrogen atoms are in pairs they do not affect the diamond's color; these
are Type IaA. If the nitrogen atoms are in large even-numbered aggregates they impart
a yellow to brown tint. About 98% of gem diamonds are type Ia, and most of these are a mixture
of IaA and IaB material: these diamonds belong to the Cape series, named after the diamond-rich
region formerly known as Cape Province in South Africa, whose deposits are largely Type
Ia. If the nitrogen atoms are dispersed throughout the crystal in isolated sites, they give the
stone an intense yellow or occasionally brown tint; the rare canary diamonds belong to this
type, which represents only 0.1% of known natural diamonds. Synthetic diamond containing
nitrogen is Type Ib. Type I diamonds absorb in both the infrared and ultraviolet region,
from 320 nm. They also have a characteristic fluorescence and visible absorption spectrum.
Type II diamonds have no measurable nitrogen impurities. Type II diamonds absorb in a different
region of the infrared, and transmit in the ultraviolet below 225 nm, unlike Type I diamonds.
They also have differing fluorescence characteristics, but no discernible visible absorption spectrum.
Type IIa diamond can be colored pink, red, or brown due to structural anomalies arising
through plastic deformation during crystal growth—these diamonds are rare, but constitute
a large percentage of Australian production. Type IIb diamonds, which account for 0.1%
of gem diamonds, are usually light blue due to scattered boron within the crystal matrix;
these diamonds are also semiconductors, unlike other diamond types. However, a blue-grey
color may also occur in Type Ia diamonds and be unrelated to boron. Also not restricted
to type are green diamonds, whose color is derived from exposure to varying quantities
of radiation. Grading white diamonds
The majority of diamonds that are mined are in a range of pale yellow or brown color that
is termed the normal color range. Diamonds that are of intense yellow or brown, or any
other color are called fancy color diamonds. Diamonds that are of the very highest purity
are totally colorless, and appear a bright white. The degree to which diamonds exhibit
body color is one of the four value factors by which diamonds are assessed.
History of color grading Color grading of diamonds was performed as
a step of sorting rough diamonds for sale by the London Diamond Syndicate.
As the diamond trade developed, early diamond grades were introduced by various parties
in the diamond trade. Without any co-operative development these early grading systems lacked
standard nomenclature, and consistency. Some early grading scales were; I, II, III; A,
AA, AAA; A, B, C. Numerous terms developed to describe diamonds of particular colors:
golconda, river, jagers, cape, blue white, fine white, and gem blue, "brown".
Grading the normal color range Refers to a grading scale for diamonds in
the normal color range used by internationally recognized laboratories. The scale ranges
from D which is totally colorless to Z which is a pale yellow or brown color. Brown diamonds
darker than K color are usually described using their letter grade, and a descriptive
phrase, for example M Faint Brown. Diamonds with more depth of color than Z color fall
into the fancy color diamond range. Diamond color is graded by comparing a sample
stone to a master stone set of diamonds. Each master stone is known to exhibit the very
least amount of body color that a diamond in that color grade may exhibit. A trained
diamond grader compares a diamond of unknown grade against the series of master stones,
assessing where in the range of color the diamond resides. This process occurs in a
lighting box, fitted with daylight equivalent lamps. Accurate color grading can only be
performed with diamond unset, as the comparison with master stones is done with diamond placed
on its table facet and pavilion side facing upwards. When color grading is done in the
mounting, the grade is expressed as an estimated color grade and commonly as a range of color.
Grading mounted diamonds involves holding the mounted diamonds table close to the table
facet of the master stone and visually comparing the diamond color under the same color conditions
as unmounted diamond grading. The resulting grade is typically less accurate, and is therefore
expressed as a range of color. While a grading laboratory will possess a complete set of
master stones representing every color grade, the independent grader working in a retail
environment 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 five diamonds in two grade increments, such as an E, G, I, K, and M.
The intermediate grades are assessed by the graders judgement.
Diamonds in the normal color range are graded loose,
Diamonds that rate toward the colorless end of the range are sometimes known as "high-color"
diamonds, and those toward the other end, "low-color" diamonds. These terms refer to
the relative desirability of color grades, not the intensity of the color itself.
Grading fancy color diamonds Yellow or brown color diamonds having color
more intense than "Z", as well as diamonds exhibiting color other than yellow or brown
are considered fancy colored diamonds. These diamonds are graded using separate systems
which indicate the characteristics of the color, and not just its presence. These color
grading systems are more similar to those used for other colored gemstones, such as
ruby, sapphire, or emerald, than they are to the system used for white diamonds.
Colored diamond grading system Diamond colors more saturated than this scale
are known as "fancy color" diamonds. Any light shade of diamond other than Light Yellow or
Light Brown automatically falls out of the scale. For instance, a pale blue diamond won't
get a "K", "N", or "S" color grade, it will get a Faint Blue, very Light Blue or Light
Blue grade. Laboratories use a list of 27 color hues that span the full spectrum for
colored gems and diamonds. A modifying color combination can also be added for stones without
the purest hues. Additionally, for diamonds the following colors are used: White, Black,
Gray, Pink, Brown. The saturation of these hues is then described with one of nine descriptors:
Faint, Very Light, Light, Fancy Light, Fancy, Fancy Dark, Fancy Intense, Fancy Deep, Fancy
Vivid. The terms 'Champagne', 'Cognac' and 'Coffee' refer to different types of brown
diamonds. In the diamond processing/dealing industry, the word 'Brown' is considered a
killer as far as diamond value goes. Even though champagne is a light yellow color,
champagne diamonds are Light Brown. Cognac is usually used to describe a diamond that
is Orangish-Brown because cognac is a deep golden-orange color. Coffee is usually used
to describe a diamond that is a Deep Brown or Vivid Brown color. Some grading agencies
may also describe brown stones as Fancy Yellowish-Brown, Fancy Light Brown, Fancy Intense Brown, etc.
Value of colored diamonds Diamonds that enter the Gemological Institute
of America's scale are valued according to their clarity and color. For example, a "D"
or "E" rated diamond is much more valuable than an "R" or "Y" rated diamond. This is
due to two effects: high-color diamonds are rarer, limiting supply; and the bright white
appearance of high-color diamonds is more desired by consumers, increasing demand. Poor
color is usually not enough to eliminate the use of diamond as a gemstone: If other gemological
characteristics of a stone are good, a low-color diamond can remain more valuable as a gem
diamond than an industrial-use diamond, and can see use in diamond jewelry.
Fancy diamonds are valued using different criteria than those used for regular diamonds.
When the color is rare, the more intensely colored a diamond is, the more valuable it
becomes. Another factor that affects the value of Fancy-Colored diamonds is fashion trends.
For example, pink diamonds fetched higher prices after Jennifer Lopez received a pink
diamond engagement ring. Extremely low grade quality has not stopped creative merchants,
such as Le Vian, from marketing Dark Brown diamonds as so-called "Chocolate Diamonds".
Fancy-colored diamonds such as the deep blue Hope Diamond are among the most valuable and
sought-after diamonds in the world. In 2009 a 7-carat blue diamond fetched the highest
price per carat ever paid for a diamond when it was sold at auction for 10.5 million Swiss
francs which is in excess of US$1.3 million per carat.
See also Diamond clarity
Diamond enhancement References
Additional Resources Color Grading "D-to-Z" Diamonds at GIA Gems
& Gemology, Winter 2008, Vol. 44, No. 4 - Details history and methodology of the GIA color scale.