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Describing Color in Gemstones, Color Communication.
by David Weinberg, Founder, Multicolour.com, Multicolour Gems Ltd.
Color Communication
As online inventory continues to grow, there are just too many
stones to look at without a color search. Few customers want to look
thru 500 pages of gemstones to find their favorite colors. The colors
of the images are usually very close but, without a verbal description,
a color search would
not be possible. Since color is so important in gemstones, customers
have always asked for verbal color descriptions. Color grading is
difficult and time consuming. Verbal color descriptions may not be as
accurate as the colors of the photographs but, if you consider both
the color grade and the color of the image on your screen, your
understanding of the stones color in the specified light conditions
should be optimized.
People perceive color differently and their impressions are probably
created from the time they receive their first set of crayons. Our
verbalization of color is based on the GIA/Munsell color grading system.
There are other ways to describe colors but the GIA/Munsell system is most
convenient for gemstones. GIA makes a 324 piece plastic color set which
we use as a standard. Missing colors can be interpolated if necessary.
The set is available at GIA website. Although
the set includes 324 colors, an additional 760+ colors can be
interpolated. Gemstones are available in millions of colors but the
1000+ color grade GIA system is probably adequate for grading.
Pantone also
produces color
sets and standards which are interesting and well worth looking into.
Pantone is a leader in color standards but their sample sets are
mostly 2-dimensional and more suitable for comparing paints and textiles.
The GIA set is 3-dimensional and the plastic pieces are faceted like
gemstones and this makes them easier to compare with real gems.
Describing Color
The Munsell
color-order system is a way of precisely specifying colors and showing the
relationships among colors. Every color has three qualities or
attributes: hue, value, and chroma. The GIA
terms are hue, tone, and saturation but the meaning is the same.
Munsell established numerical
scales with visually uniform steps for each of these attributes.
These attributes are given the symbols H,V, and C and are written
in a form H V/C, which is called the Munsell notation. Utilizing
Munsell notations, each color has a logical relationship to all
other colors. The Munsell sets are too detailed to describe verbally.
GIA selected 31 Munsell hues for their gem set and by naming and
verbalizing the other numerical attributes, they were able to
achieve a reasonably accurate system for expressing color in gemstones.
Hue
Hue is that attribute of a color by which we distinguish red
from green and blue from yellow. Hue is the basic impression of color
that we notice immediately - the component that gives it its family name
like red , blue, yellow, or green. There is a natural order of hues: red,
yellow, green, blue, purple. One can mix paints of adjacent colors in this
series and obtain a continuous variation from one color to the other.
There are millions of hues but the human eye can actually discern around 150.
Basic hue names are familiar like orange, green, violet and purple. These
are modified to indicate where other hues lie like bluish or greenish, plus
adjectives like slightly and strongly. Thus, a hue that is predominately
blue with a hint of green is very slightly greenish blue.
Saturation or Chroma
Saturation or chroma is the strength, purity or intensity
of the hue present in a color sensation. Colors of low saturation are
sometimes called weak, grayish or brownish while those of high saturation
are said to be highly saturated, strong or vivid. Imagine mixing a vivid
orange paint, a little at a time, with a gray paint of the same value.
If you started with gray and gradually added orange until the vivid orange
color was obtained, you would develop a series of gradually changing colors
that increase in saturation. Saturation is assessed on a 7 level scale with
corresponding word terms ranging from neutral to vivid.
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| 1 |
grayish (brownish) |
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| 2 |
slightly grayish(brownish |
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| 3 |
very slightly grayish(brownish) |
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| 4 |
moderately strong |
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| 5 |
strong |
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| 6 |
vivid |
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Tone or Value
Tone or Value indicates the lightness or darkness of
a color sensation. The scale of values range from 0 for pure black to
10 for pure white. Black and white and the grays between them are called
neutral colors. They have no hue. Colors that have a hue are called
chromatic colors. Colors that do not have a hue are known as achromatic.
The value scale applies to chromatic as well as to neutral colors.
GIA uses 7 of those steps (Tones 2 thru 8) for grading tone in transparent
colored gemstones.
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| 0 |
colorless or white |
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| 1 |
extremely light |
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| 2 |
very light |
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| 3 |
light |
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| 4 |
medium light |
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| 5 |
medium |
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| 6 |
medium dark |
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| 7 |
dark |
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| 8 |
very dark |
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Light Source
An artificial daylight tube 6200K used for color grading and a
similar light for photographing most of gemstones. Incandescent light
used for photography to improve resolution in some stones including color
change stones, pink sapphires, and Songea rubies. Colorless stones are
photographed without lighting.
Real natural daylight is impractical because of its variability.
Please see the chart (Temperature and Typical Light Sources ) below
which illustrates the point.
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| 1000K |
Candles; oil lamps |
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| 2000K |
Very early sunrise; low effect tungsten lamps |
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| 2500K |
Household light bulbs |
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| 3000K |
Studio lights, photo floods |
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| 4000K |
Clear flashbulbs |
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| 5000K |
Typical daylight; electronic flash |
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| 5500K |
The sun at noon near Kodak´s office |
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| 6000K |
Bright sunshine with clear sky |
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| 7000K |
Slightly overcast sky |
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| 8000K |
Hazy sky |
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| 9000K |
Open shade on clear day |
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| 10,000K |
Heavily overcast sky |
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| 11,000K |
Sunless blue skies |
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| 20,000K |
Open shade in mountains on a really clear day |
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Limitations and Practical Grading
The GIA color grading system is not perfect but it its pretty
good and many jewelers, gemologists and gem traders already use it.
Tantalizing descriptions like hot pink, ultra neon blue, Kelly green,
cinnamon pink, sky blue or AAA color all sound good but they are
just names without specific meanings. They are useful in a general
sense but without a standardized master set and standardized lighting,
they are too subjective to communicate color very meaningfully.
Color correct gemstone photography is our ultimate objective and in
most cases the colors of our images will be even more specific than
the verbal description. However, since the colors of images do show
some variations depending on the computer, the screen settings, and
the monitor quality, it is important to consider both the image and
the color description.
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