Evaluating Gem Color: Hue, Tone, and Saturation

Step 4: Gem Grading

Lesson 7


Gem color is one of the most important elements in gemstone grading. Subtle variations can make a substantial difference in value. Novice gemologists must learn to accurately describe colors. Many color description systems exist, since industries that deal with colors have developed highly refined methods. Some gemologists use the Munsell system, popular in the photographic industry.

The gem industry has also produced several systems. (Seemingly, every year someone comes out with a new method). However, only the Gemological Institute of America (GIA) system has gained anything close to widespread acceptance. Since it’s taught to all GIA students, this system has the largest user base. Still, the colored stone industry has resisted it as a standard. What’s the concern? Establishing a standard will change the existing value of many colored gems. For example, the value of all rubies with a certain tone and hue could decrease. This would be disastrous for everyone holding such stones. Colored stone grading is too complex for a simple system like the one used for diamonds.

There are many ways to describe and grade gem color. We’ll begin with one of the simplest, but …

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Full Article Details

Content Length 4205 words
Reading time 21 min 1 sec

Here's what you get if you unlock this article:

  • Introduction
  • The Inverted “U” Gem Color Description Method
  • The GIA Gem Color System
    • Hue
    • Tone
      • Extinction
    • Saturation
    • Gem Values and Saturation
  • Gem Color Grading Examples
  • Creating The Proper Environment for Gem Color Grading
    • Room Colors
    • Eyewear
    • Lighting Sources
      • Natural Light
      • Incandescent
      • Fluorescent
      • A Note on Gem Color Change Phenomena
    • Brightness
  • Gem Color Grading Procedures
    • Initial Inspection
    • Describe the Hue
    • Describe the Tone
    • Describe the Saturation
    • Writing Your Gem Color Description
    • Don't Rely on Illustrations
  • Special Considerations for Grading Gem Color
    • Structural Colors
    • Color Change
    • Set Stones
    • Windowing
    • Pleochroic Gems
    • Color Zoning
      • Intentional Zoning
      • Unintentional Zoning
    • Grading Multi-Colored Stones
  • Species Specific Gem Color Grading
    • Amethyst
    • Aquamarine
    • Garnet
    • Kunzite
    • Morganite
    • Sapphire
    • Ruby
    • Blue Topaz
  • Consider the Source When Evaluating Gem Color
  • Hue Specific Considerations for Gem Color Grading
    • Blue Gems
    • Green Gems
    • Red Gems

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