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 Home / Gem Library / Columns / Color Communication March 29, 2017  

Describing Color in Gemstones, Color Communication.
by David Weinberg

As our 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 our 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. Our verbal color descriptions may not be as accurate as the colors of our 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 GIA/Munsell system.

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 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 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.

1 grayish (brownish)
2 slightly grayish(brownish
3 very slightly grayish(brownish)
4 moderately strong
5 strong
6 vivid

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.

0 colorless or white
1 extremely light
2 very light
3 light
4 medium light
5 medium
6 medium dark
7 dark
7 very dark

How do we color grade?

When we judge hue and saturation (chroma), we locate and grade the KEY COLORS. We view the stone face up and find the Key colors - the colors under the crown facets which show the best representation of color in the stone. We grade hue and saturation by looking only at the KEY COLORS. We do not consider washed out, windowed, or areas of extinction.

  1. Windowing refers to the washed out area in the center of a stone generally seen through the table. A stone with a large washed out area is said to have a large window.
  2. Extinction refers to the areas of darkness visible through the crown. These areas appear gray or black.
  3. Brilliance is a measure of the light which enters the stone and reflects back to our eye. It is seen as the bright areas or flashes within the stone. This most attractive reflected light is also known as the KEY COLOR.

Tone or Value is graded from the observation of lightness or darkness in a gemstone. Extinction, brilliance and windowing are all considered. Is the color light or dark? How dark?

What light source do we use for color grading? For Photographing? Why do we use artificial light?

We use an artificial daylight tube 6200K for color grading and a similar light for photographing most of our stones. Although we always color grade with the same 6200k light, we do use incandescent lights 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 below which illustrates the point.

Temperature Typical Sources
1000K Candles; oil lamps
2000K Very early sunrise; low effect tungsten lamps
2500K Household light bulbs
3000K Studio lights, photo floods
4000K Clear flashbulbs
5000K Typical daylight; electronic flash
5500K The sun at noon near Kodak's office
6000K Bright sunshine with clear sky
7000K Slightly overcast sky
8000K Hazy sky
9000K Open shade on clear day
10,000K Heavily overcast sky
11,000K Sunless blue skies
20,000K Open shade in mountains on a really clear day

Limitations, 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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