The Limitations of Color-Chart Systems for Gemstone Color Measurements
Until the mid-80s, little progress was made, despite the appearance and widespread promotion of various color-chart systems. None of these systems are satisfactory for gemology, chiefly because: 1. They don’t adequately cover the total range of gem colors, 2. They don’t offer enough detail in the ranges they do cover, and 3. The color-chart materials (printed colors and transparencies) are of insufficient quality to prevent variations in production runs.
Three-Dimensional Color Space
The science of colorimetry is well established in almost all areas of endeavor where color is important, such as paint, plastics, textiles, and other industrial and consumer materials. Objective instrumentation is now routinely used in these fields. However, before such instruments were available people had to rely on visual systems such as color charts for specifying color. These charts are sections of what we may refer to as three-dimensional color space. These dimensions are termed hue, lightness, and saturation.
Hue is the attribute we are describing when we speak of red, yellow, green, blue, purple, and other hues intermediate to adjacent pairs in this series. These hues can be readily visualized in terms of a color wheel.