Value Factors, Design, and Cut Quality of Colored Gemstones (Non-Diamond)

Posted on March 31, 2020 by Al Gilbertson, GG (GIA), CG (AGS)

In this comprehensive article, the author discusses the value factors of colored gems in five parts. Parts one and two appeared in Gem Market News, January/February 2016, Volume 35, Issue 1. What follows are parts three and four.

Part 3: Darkness and Brightness

Part 1 discussed the major value factors that affect the price of a colored gemstone, and broke down the various aspects of cut quality (one of the factors of value). Part 2 defined aspects of cutting styles to establish some common language, with a focus on basic faceting styles, and a short discussion on cabochons and beads. Since the color quality is such an important part of the value, parts 3 and 4 will focus on factors that affect value related to color, and examine how a cutter makes choices when cutting a gem.

Wireframes or depictions of facet arrangements (such as the left side of Fig. 3-09) are from scans of real gems so as to illustrate aspects of gem cutting. Face-up patterns (such as the right side of Fig. 3-09) were made using the program DiamCalc; adjustments were made to the refractive index to represent the gem material being demonstrated. DiamCalc does not show double refraction.

Fig 3 11
Fig. 3-11. Citrine top and side view. Pre-formed by Werner Anschvetz, cut and polished by Hans J. Roehrig. Photo by Orasa Weldon, © GIA.


Before discussing how the trade assesses relative value of colored gems, it is important to realize that you will often see examples where the cutter had to….

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