Color Description Based on Visual Observations. A gemstone’s color can be described by three attributes: hue, tone (the lightness or darkness of the color), and saturation (the degree of intensity of the color). The colors of the gemstones were described using terminology from the GIA Colored Stone Grading System, as well as the Gemewizard software program that displays arrays of images of faceted colored gemstones in three-dimensional color space, along with the description of the color for each.
Components of Color
Hue. The GIA Colored Stone Grading System uses 31 hue names to describe the basic colors of colored gemstones.
|Purple (P)||yellowish Orange (yO)||bluish Green (bG)|
|reddish Purple (rP)||orangy Yellow (oY)||very strongly bluish Green (vstbG)|
|Red-Purple or Purple-Red (RP/PR)||Yellow||Green-Blue or Blue-Green (GB/BG)|
|strongly purplish Red (stpR)||greenish Yellow||very strongly greenish Blue (vstgB)|
|slightly purplish Red (slpR)||Yellow-Green or Green-Yellow (YG/GY)||greenish Blue (gB)|
|Red (R)||strongly yellowish Green (styG)||very slightly greenish Blue (vslgB)|
|orangy Red (oR)||yellowish Green (yG)||Blue (B)|
|Red-Orange or Orange-Red (RO/OR)||slightly yellowish Green (slyG)||violetish Blue (vB)|
|reddish Orange (rO)||Green (G)||bluish Violet (bV)|
|Orange (O)||very slightly bluish Green (vslbG)||Violet (V)|
|violetish Purple (vP)|
Tone. The system also uses seven terms to describe the tone of a gemstone’s color.
Saturation. The system uses certain terms to describe saturation for both “warm” (upper row) and “cool” (lower row) colors.
A gemstone’s color description is written as: [tone], [saturation], and [hue] (for example: Light, slightly grayish, Blue or Medium dark, moderately strong, slightly purplish Red). In the case of a multi-colored gemstone, two or more color descriptions may be given.
Gemstones that Exhibit More than One Color. In some instances (mainly tourmalines), a gemstone exhibited more than one color. This color difference is visual evidence of a difference in chemical composition or other color causes between the color zones. In such instances, we attempted to document any differences in gemological properties between the color zones—these variations were most likely to occur in refractive index, absorption spectrum, ultraviolet fluorescence, and pleochroic colors. Whenever possible, these differences were noted and recorded. For example, an elbaite tourmaline with distinct red and colorless zones with differing refractive indices would be described as (Red) 1.625, 1.641 / (Colorless) 1.620, 1.640.