Shopping for colored gemstones can be fun.
What should you buy? The ones you like of
course! When you're out comparing stones,
look for evenness of color as opposed to dead
spots or areas where the color is more or
less intense (known as color zoning). Also
look for "windowing." This is when
you can look right through the stone without
seeing much color or brilliance, like looking
through a colored window. Most importantly,
if you compare stones you'll see which ones
look nice and which ones are boring.
Our intention here is to give you enough tools
and guidance to hopefully better evaluate
color stones. In many ways buying a color
stone is easier than purchasing a diamond.
Your main criteria when evaluating a color
stone should be, its color!
Altogether, you should look at the following
factors: Color, Clarity, Cut, Carat weight,
Shape of the stone, Transparency, Treatments,
Distinctive phenomena.
The color that one sees when looking at a
mineral or gemstone are due to the response
of that person's eye to the energies of the
light, the emission spectrum of the illumination,
and most importantly, physical phenomena in
the material that cause some colors to be
absorbed while others are undisturbed or enhanced.
It is beyond the scope of this talk to go
over physiology of eye that allows us to see
colors, or to dwell on the emission spectra
of various light sources, and etc. Rather,
we will concentrate on explaining main factors
to better describe the color(s) of a gemstone.
Color can be described by three main components:
Hue, Saturation, and Tone.
Hue refers to the basic
color : Red, Orange, Yellow,
Green, Blue, Violet, Purple, etc., as well
as transition colors such as bluish green,
yellowish green, etc. (It is noted here that
there is a difference between purple and violet.
Violet falls between blue and purple. Purple
falls between red and violet, so it is much
more reddish than violet.). Brown, black,
gray and white are not considered to be hues.
Some colored stones will have a dominant hue
and a secondary hues. When looking at the
stone from different directions while moving
it, different colors may be seen. This is
due to certain optical properties of the stone.
To determine the hue, it is recommended to
look for the dominant color in the face up
view, and trust your first overall impression.
Keep in mind that the most expensive hues
are not necessarily the ones which will look
good on you. If you don't plan to resell your
stone, there is absolutely no need to complicate
matters and base your choice of hue on trade
references. Just choose the color you like
best and that fits your budget.
It is noted here that "lighting"
does matter and it affects gemstone color.
The whitest, most neutral light is at midday.
Besides adding the least amount of color,
this light makes it easier to see the various
nuances of color. Consequently, you should
judge gemstone color under a daylight equivalent
light. Incandescent light bulbs may add red
(red colors strengthened, warm colors appear
more alike, grayish colors may look brownish,
and green may look darker and a little more
yellowish or less bluish). Fluorescent lights,
depending on what type they are, most strengthen
blue colors (warm white tubes add yellow).
Light under an overcast sky or in the shade
may add blue or gray (reds appear more purplish,
greens and purples look more bluish, yellows
look greener, and blues appear stronger).
The GIA has 31 Hues and the complete GIA GemSet®
has 324 sample hue colors with varying Tones
and Saturations. In addition we put RGB (Red
Green Blue) and HEX codes for your reference.
The degree to which the hue is masked (or
hidden) by brown or gray. It is described
as the strength or purity of a Hue. Saturation
is also sometimes called "Intensity"
or "Color Mask". Stones with high
saturation, for example, have hardly any gray
or brown masking the hue.
The GIA Saturation Scale is from 1 to 6. The
lower numbers such as 1, 2 or 3 of warm colors
such as red, orange or yellow tend to look
brownish, and the cool colors such as blue
and green tend to look grayish. Level 4 no
longer shows either grayishness or brownishness,
while neither is strong or weak. Level 5 is
strong and level 6 being vivid, almost over
colored.
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Saturation
scale (medium dark stone)
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Warm
Colors
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Cool
Colors
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Refers to the depth of color, or relative
lightness or darkness of a Hue. Tone is the
scale from light to dark, regardless of color.
The lightest possible tone is "Colorless"
and the darkest is "Black". The
GIA Tone Scale is divided into 11 grades,
0 to 10, with 0 being colorless to 10 being
black:
Key Scale Code Name Hex RGB
| Tone
Scale |
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| 1 |
2 |
3 |
4 |
5 |
6 |
7 |
8 |
9 |
10 |
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Stones
with a high color saturation, for example,
have hardly any gray or brown masking the
hue. When the color of the stone is described
as saturated, it means that it has high
saturation and also good depth of color
(tone). See below figure for better understanding
of this two terms working together:
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