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Diamonds are found in all colors of the rainbow, from clear, colorless,
transparent stones to ink black ones. Colors of high saturation such
as red and green, which have no modifying secondary colors, are very
rare indeed and command world record prices. Collectively, these colored
diamonds are called "fancy colored" diamonds, and include the fancy
colored yellow diamonds found at the far end of the color spectrum
of the so-called "white or colorless" stones we will focus on here.
A discussion of the variety and causes of the different colors, which
occur in fancy colored diamonds, can be found
elsewhere on this site.
The best color for a colorless diamond is, in fact, an absence
of color. However these stones are relatively rare, the most frequently
found diamonds (~80%) being of industrial quality. Those suitable
for gem use (~20%) usually have some yellow tint, due to the presence
of a small amount of contaminating nitrogen. As one would predict,
a truly colorless stone will carry a premium price, and the larger
that diamond, the greater the premium per carat. For every carat
of polished gem quality diamond, about 250 tons of diamond-bearing
earth (kimberlite) must be mined.
Diamonds are graded for color only as loose, unmounted stones
in the inverted position (table down, pavilion up), and under very
specific conditions of lighting and background, and also the distance
and angle of the observer in relation to the stone. A color scale
has been devised by the Gem Trade Lab. of the Gemological Institute
of America (GIA) divided alphabetically from D (the absence of color)
to Z (fancy yellow color), and is recognized world-wide. Each letter
grade represents a small range of color, and not just a single color.
Diamonds are color graded by being compared to a set of master stones.
Another important and well-respected grading lab is the American
Gem Society Labs., which uses a similar grading system, but a numerical
scale from 0 to 10 (See figure below).
Because both GIA and AGS grading labs. are known to be strict
and accurate in their color and clarity grading, Dutton's Diamonds
sells diamonds with ONLY these grading reports (certificates, certs)
and no others.
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Colors D, E and F are essentially without color and differ more
in transparency. Colors G, H, I and sometimes J, will usually show
little or no color in the face-up position (as set in jewelry) for
most diamond shapes. However, emerald cut diamonds, which have a
large table and large, parallel, step-cut facets will more easily
show color from G and above, especially in larger stones. Conversely,
sometimes very well cut, round brilliant diamonds of ideal or super-ideal
cut quality may show slightly less color than the grade given.
Effect of color on price: In general, as the amount of
yellow in the stone increases, the value of a diamond decreases,
that is until the fancy color grades are reached, and then the value
goes up again. Roughly, for an internally flawless (IF) round brilliant
diamond of 1-1.5ct., prices fall about 25% in going from D to E
color, and then about 10% more for each additional grade (F=-35%,
G=-45, H=-55%) until one gets to H color, where the difference decreases
to about 5% less going from H to I color (I=-60%). So the first
color decrease from D to E will provide you with by far the largest
increment in saving money. Please keep in mind that these numbers
are only rough estimates, and are not meant to be used as a pricing
guide.
Dutton's Diamonds only infrequently offers diamonds of less
than I color, and never sells diamonds of less than M color.
Factors Affecting Color
Other factors which can affect color include fluorescence, color
enhancements such as high pressure, high temperature treatment (HPHT)
and irradiation.
Fluorescence, produced by ultraviolet light from the sun,
by black lighting or other long-wavelength UV source, occurs in
an estimated 35% of gem grade diamonds. (Virtually all diamonds
fluoresce when exposed to X-rays, and this forms the basis for their
identification and collection at mining sites.) The UV light excites
electrons in the diamond crystal, which then release this absorbed
energy in the form of visible light, producing a blue, or sometimes
other color, of faint to very strong intensity. Once the light source
is removed however, the fluorescence is no longer observed. If,
in rare situations, light emission continues for a period after
the exciting light has been turned off, the phenomenon is called
phosphorescence.
Blue fluorescence, if strong or very strong, may alter the perceived
color of a diamond in a negative or positive way. For example, stones
in the colorless/near colorless ranges (D-H) may appear milky or
oily, detracting from their appearance. On the other hand, diamonds
in the lower, more yellow color ranges (I and lower) may appear
to have less yellow color due to the fluorescence, adding positively
to their appearance. Thus, the trade will slightly discount prices
of diamonds in the former category, while sometimes adding a very
slight premium to those in the latter.
The presence and color (most frequently blue, but can be any color)
of fluorescence and its intensity (none/inert, faint, medium, strong,
very strong) are indicated on all GIA and AGS grading reports. However,
these terms are considered by GIA to be only descriptive, and are
not grading terms. (For an in depth study of blue fluorescence in
diamonds, see: Gems and Gemology, Vol. 33, Winter, 1997, pp. 244-259.)
When shopping for a diamond, check to see if it has fluorescence.
If it does make sure that it is BLUE and not some other color. The
last thing you want in a colorless diamond is a potentially interfering
fluorescing background color such as yellow, green or orange, which
might greatly detract from the stone's appearance. If the diamond
has blue fluorescence, it probably won't be a factor in the stone's
appearance UNLESS the intensity is strong or greater, and even then
only infrequently is it a problem. Nevertheless, make sure you
verify that there is no effect of fluorescence under all conditions
of lighting - from bright sunlight to all types of artificial lighting.
High Pressure/High Temperature (HPHT) treatment, is a process
developed by General Electric whereby type IIa diamonds of low color
(N-O) or even fancy brown color, can be converted to colorless/near
colorless (D-H) forms by an annealing process involving high pressure
and temperature. For details, see: Gems and Gemology, Vol. 36, Fall,
2000, pp. 192-215. There is some concern that these color-enhanced
stones may come to market undetected, but new research has shown
that they can be largely detected using expensive and sophisticated
equipment. Similarly, the HPHT technique has also been applied to
type Ia brown diamonds by several companies, yielding fancy yellowish
green and greenish yellow colors. Pink and blue colors have also
been produced by the same technique.
Irradiation of diamonds using a nuclear reactor or linear
accelerator, sometimes in combination with heating, is used to produce
a variety of different fancy colored stones.
Dutton's Diamonds does not sell, or deal in diamonds that are
color enhanced in any way, so you can be assured that you will not
receive an artificially enhanced stone from us!
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