Colored Gemstone Grading & Grading Reports
Comprehensive color grading is an extremely important factor in determining the value of colored gemstones. Unlike diamonds, where the cut is one of the most important factors, the "color" of colored gemstones such as emeralds, rubies, sapphires, and tanzanite can influence as much as fifty percent of a gemstone's value.
The evaluation of colored gemstones had no generally accepted system for quantifying color and color quality before the 1900's. An American painter and art instructor named Albert H. Munsell was the first to identify three basic qualities of a specific color - hue, saturation and tone. Albert Munsell authored two books on the subject: "A Color Notation" (1905) and the "Atlas of the Munsell Color System" (1915), and the GIA eventually adopted these principles to create a standardized gemstone color-grading system.
Gemstone color grading is broken into three quantifiable categories: intensity (saturation), hue (color), and tone (lightness/darkness). The GIA specifies and labels up to thirty one gemstone hues. The "hue" is the actual "color" of the material (blue, geen, red, etc.).
This hue color chart is only an approximation of the GIA color-naming scheme, and should not be used to "evaluate" gem color. In addition, the accuracy and/or reliability of any color chart that is displayed on a website is only as "accurate" as the color calibration of the computer monitor it is displayed on.
The GIA nomenclature also specifies six levels of saturation ranging from "grayish" (neutral grey) to "moderately strong" to "vivid." The term "intensity" is also used to describe a stone's saturation.
The above example shows blue as the hue, but these same levels of color saturation could be applied to any of the hues in the uppermost chart.
To describe the darkness or lightness (similar to opacity or transparency) of a colored or colorless stone, the GIA system uses a 0–10 numerical scale with levels of tonal value ranging from "0" which represents totally clear (colorless or white) and "1" which is known as "very very light" or "extremely light," to "10" which is known as "very very dark" to "black."
With the exception of hue, each of these parameters by themselves are relatively meaningless and they must be used in conjunction to tell the full story of a gem's color quality. Taken together, these three parameters will provide a simple numeric code that can quickly and accurately quantify gemstone color.
Using a Kashmir, or "Cornflower blue" sapphire as an example, in order to receive a perfect "10" quality rating, the stone would posses a "violetish/blue" hue, with a "6" or "medium dark" tone, and a "6" or "vivid" saturation.
Please Note: The only truly accurate color evaluation chart is one that was printed by a respected testing authority — such as the GIA GemSet® hue/tone/saturation chart or Gemewizard's GemePro® color communication system  — using their proprietary CMYK/RGB/Hexadecimal color formulas that match their specific nomenclature and color-naming schemes.
Colored Gemstone Certificates & Reports
There are several trusted and reliable testing agencies that provide detailed gem grading reports but fall short when it comes to classifying colored gemstones. Reports for colored gemstones are not as systematic, methodical and detailed as a diamond grading report, but they do provide verified baseline data that can assist in appraising, isuring, and reselling a colored gemstone. Additionally, these reports vary significantly from agency to agency so if you are planning on obtaining a color grading report it is important to understand the difference.
Some level of standardization in the accepted naming and typing of gem species, colors and gem treatments is essential to fostering consumer awareness. There are seven gemological testing labs that belong to the "Laboratory Manual Harmonization Committee" (LMHC), which seeks to provide uniform standards in gem nomenclature (see list below). The World Jewellery Confederation (CIBJO) also seeks to encourage both harmonization, and international cooperation in jewellery industry trade practices.
A GIA (Gemological Institute of America) report (above, center) provides detailed information about the dimensions, carat weight, shape and cut of a stone. GIA reports also cover any treatments or enhancements that have been done and of corse, wether the stone is natural or synthetic. A GIA report utilizes a "colored stone grading system" chart to graph the hue, tone, and saturation of a stone.
An AGTA (American Gem Trade Association) report (above, left) provides the usual detailed information about the dimensions, carat weight, shape, cut, and enhancements of a stone, and will also will include a photograph. The AGTA report will also comment on the lack of any heat-treatments and the corresponding increase in value for untreated stones. an AGTA report will also state the geographical origin of a stone (ie. ruby or sapphire), which can significantly affect its value (ie. Burmese ruby). AGTA does not however, use the GIAs more extensive hue scale and does not take into account the tone or saturation.
An AGL (American Gemological Laboratories) report (above, right) also provides detailed information about the dimensions, carat weight, shape, cut, and enhancements of a stone. AGL reports also include an illustrated diagram of the stone that shows cut and clarity information. AGL uses proprietary color and clarity grading that is completely different from the GIA standard and therefor, difficult for a layperson to understand. Color grading is defined as: "Color Rating/Tone" and is graded on a scale from 1 (excellent) to 10 (poor). A numeric value for color is given under "Color Scan". The testing light source is also identified. An AGL certification also provides information on the stone's country of origin, and identifies any gem enhancements or treatments.
The Gübelin Gem Laboratory in Lucerne, Switzerland is one of the leading testing laboratories in Europe, testing colored stones, fancy colored diamonds, colorless diamonds, and pearls. They are also on the cutting edge for testing diamonds for any sign of (HTHP) enhancement. Colored stones are tested for the usual parameters of clarity, color, cut, and enhancements as well as place of origin. Diamonds are tested for clarity, color, flourecence, cut, and symmetry. GGLs pearl report is fairly basic, and does not address nacre thickness.
LMHC Colored Gem Testing Laboratories
Gemological Institute of America (GIA)
5345 Armada Drive
Carlsbad, California 92008
Tel: (800) 421 7250
American Gem Trade Association (AGTA)
18 East 48th Street, Suite 502
New York, New York 10017 USA
Tel: (212) 752 1717
Centro Informazione e Servizi Gemmologici SpA (CISGEM)
via delle Orsole, 4
20123 Milano, Italy
Tel: (2) 8515 5250
Gemmological Association of All Japan Co., Ltd. (GAAJ)
Daiwa-Ueno Bldg. 7F, 5-25-11
Ueno, Taito-ku, Tokyo, 110-0005, Japan
Gem and Jewelry Institute of Thailand (GIT)
140, 140/1-3, 140/5 ITF - Tower Building. 1st - 4th and 6th Floor,
Silom Road, Suriyawong, Bangrak,
Tel: (662) 634 4999, Fax: (662) 634 4970
Gübelin Gem Laboratory Ltd. (GGL)
6006 Lucerne Switzerland
Tel: (+ 41) 41 / 429 17 17
Swiss Gemmological Institute (SSEF)
CH-4001 Basel, Switzerland
Tel: (+ 41) 61 262 06 40
Note: The seven labs above are LMHC (Laboratory Manual Harmonisation Committee) members
Other Gemological Testing Laboratories
American Gemological Laboratories (AGL)
580 Fifth Avenue
New York, New York 10038
Tel: (212) 704 0727
American Gem Society Laboratories (AGSL)
8917 West Sahara Avenue
Las Vegas, Nevada 89117
Tel: (702) 233 6120
European Gemological Laboratory USA (EGL)
6 West 48th Street
New York, New York 10036
Tel: (212) 730 7380
International Gemological Institute (IGI)
589 Fifth Avenue
New York, NY 10017 USA (offices worldwide)
Tel: (212) 753 7100
Österreichische Gemmologische Gesellschaft (SSEF)
1150 Wien (Vienna), Austria
Tel: (+ 43) 01 231 22 38 od. 0676/310 40 66
Laboratoire Français de Gemmologie (LFG)
2, place de la Bourse
75002 Paris, France
Tel: (+ 33) 1 40 26 25 45
Gemmological Institute of India (GII)
29 Gurukul Chambers
187-189 Mumbadevi Road
Bombay 400 002, India
Tel: (+ 91) 22 2342 00 39
Gem Testing, Standards, & Trade Organizations
The World Jewellery Confederation (CIBJO)
(Confédération Internationale de la Bijouterie, Joaillerie et Orfèvrerie)
Piazzale Carlo Magno, 1
20149 Milano, Italy
Tel: (+ 39) 02 4997 7098
Bibliography & Suggestions for Further Study on Colored Gemstone Certificates
1. GIA, How GIA Identifies Colored Stones . www.gia.edu
2. GemEwizard, GemePro Color Communication . www.gemewizard.com
3. JCRS, Colored Stone Certificates . www.jcrs.com
4. Gemval.com, 32-bit Web Color Communication System . www.gemval.com
5. Modern Jeweler, Guide to Gem Lab Reports . archives.modernjeweler.com
6. ICA, All About Colored Gemstones . The Colored Gem Association
7. UC Berkeley, Color in Minerals . Berkeley.edu
8. Gemstone Forecaster, GIA's Colored Stone Grading System . www.preciousgemstones.com
9. Kurt Nassau, The Origins of Color in Minerals . American Mineralogist
10. Sarin, Diamond Color Grading & Gemology Tools . Sarin Gem Labs
11. Martin D. Haske, Measuring Color Via Spectrophotometer . AGL Adamas Gemological Laboratory