Grading Natural Color Diamonds
Natural Color Diamonds are evaluated from the "face up"
position, meaning gemologists look directly through the top of the
diamond. Experts at both the Gemological Institute of America (GIA)
and the International Gemological Institute (IGI) have three
parameters by which they describe color for these exquisite stones:
Hue, Tone and Saturation.
Color Hue
Color hue refers to the dominant color of the stone, such as pink,
yellow, blue. There can also be modifiers or tints, which impart
more than one hue to the stone, casting it into a still separate
color category. For instance, a purplish-pink diamond indicates a
stone with principal pink hue and purplish tints. If no such tints
are present, the hue of the stone is said to be a pure primary
color.
Color Tone
Color Tone refers to how much lightness or darkness a stone
appears to retain even when illuminated. The range, obviously, is
from light or very light, to dark or very dark.
Color Saturation
Color Saturation describes the strength or intensity of the hue or
main color. The saturation of light toned diamonds can vary from a
pastel to vivid and intense. Darker diamonds will range from dark
to deep in description.
How Color Is Graded
Natural Color Diamonds are graded by gemological laboratories in
very high-tech environments under controlled lighting environments
similar to natural daylight. First, diamonds are tested for
treatment, synthetic additions or alterations to ensure
authenticity. Most laboratories will scan diamonds with a
spectroscope to compare readings with their historical data and
utilize High-Pressure-High-Temperature (HPHT, the most common
process used to enhance the color of diamonds) detection and other
proprietary equipment. Gemologists will also use comparison stones
and proprietary color chips to compare two diamonds to each other.
Though the face-up appearance is ultimately what determines the
diamond color, stones are evaluated from other angles as well.
Grading Reports
Two types of reports are available:
- Full Certificates provide full details about a stone including
clarity, symmetry and polish
- Color-only certificates that provide color grading for natural
fancy colored diamonds.
"Grading the color of the colored diamond is one of the greatest
challenges in gemology... the challenge has been to apply
scientific, yet practical, time-tested standards to such rarities
of nature…" G&G (Gems & Gemology), Color Grading of Colored
Diamonds in the GIA Gem Trade Laboratory
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