GemeWizard
Home|About Us|Store|Color Report Newsletter|Support|News & Events|Contact|Gemstones Colors

Gemstones Colors and Prices



         


   

      Gemewizard archive daily article




Figure 1


Figure 2

  The whole is not always the sum of its parts

By Guy Borenstein
January 16, 2013


One of the best features in GemePro™, Gemewizard's color communications and analysis system, is the Sampler, an automatic color analysis feature for imported images. It is an excellent tool for determining a gem's color, but in special cases it provides data that, while accurate, could be incorrectly interpreted by an inexperienced user.

This is the case with multi-colored or distinct pleochroic gems, and with gems displaying optical phenomena, such as play of color, asterism, shine. In these cases, we use several special techniques to obtain the unambiguous color analysis results, as demonstrated in our February 2012, May 2012, September 2012 and December 2012 issues.

However, there is another interesting case that we may at times overlook, and that is the cut and its effect on color. Sometimes, the analyzed polished gem reflects contrasting colors from its inner facets. This appearance is common for step cuts, such as emerald cuts and baguettes. Although the reflected colors look distinctly different, the Sampler mixes them together to create average results, which are often meaningless and cannot be used. To overcome this issue, the Sampler also returns the dominant colors it has identified. In essence they are the separated reflected rays, and are the colors that are key for obtaining a correct analysis.

To illustrate the issue, we took images of pink spinel gems in different cutting styles, which provide the same average colors when analyzed using the Sampler. For each gem, we identified the dominant colors and their location within the gem.

Figure 1 features two noticeably different spinels. Both gems, although easily distinguishable by sight, obtained the same average color (Gemewizard color code 2-4-3). Viewing the dominant colors of each, we can see that for the emerald-cut spinel A, there is practically an even ratio between the lighter shades emanating from the long facets and darker shades from the short and the cornered facets, made up of closely related hues (red and orangy Red). However, in the oval-shaped spinel B, the colors are from three hues (Red, orangy Red and Orange-Red), with an uneven ratio between them (most of the gem color is composed of 2-4-4 reflections).

Similar results were found in Figure 2. Three different polished spinels were analyzed. None of the three look similar to each other, however each produced the same average color (1-4-3). The oval-shaped spinel A was identified as comprising three colors, where most of which (90 percent) is composed of two closely related, lighter hues and one darker hue with almost no influence. In contrast, the B and C spinels, which were emerald-cut and baguette-shaped, returned two distinctly different colors, one lighter and one darker. The colors were distributed within the gem in a clear pattern of outer and inner facets. By mixing them together, we received, for each, the same hue as the one detected in the spinel A.

Figures 1 and 2 demonstrate the issue. For step cut stones, where the distance (in the color space) between the reflected colors is wide, the Sampler's average color is misleading. Instead, we need to look at both the gem itself and the dominant colors detected by the Sampler.

Judging the color of a gem is not always a simple "click and retrieve" process; the role of the human examiner remains critical. Even the best tools - and we are confident that GemePro™ and the Sampler are among the best - are at most tools that assist in making a final decision. The final call is always yours, and a degree of gemological knowledge and grading experience will make the use of the tool more efficient.

It's not case of the worker being as good as his tools, but rather a case of the tools being as good as the worker.

©2007 Menahem Sevdermish, GemEwizard, Inc. All Rights Reserved. Designed by YCS - Yahalom Creative Solutions