Angles for Cutting Garnets
Cutting garnets and other color saturated gems for brilliance can be challenging. Here's some advice for choosing the best angles for color and brilliance.
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Cutting Garnets Shallow
The color saturation of a gem depends directly on how long a distance light travels through it. You can easily darken the color of a gem by making it deeper. Or lighten it by keeping it shallow.
Just how shallow is the question here. Some garnets come in large sizes. You might need to play with the angles quite a bit. Most garnets have a refractive index (RI) between 1.74 (pyrope and grossular) and 1.8 (almandine and malaya). This gives them a critical angle of 35 to 33°.
Cutting on the Critical Angle
The angle for maximum brilliance of a colorless stone in this RI range would be 42°. However, on a large garnet, that angle would make the stone so deep that the color absorption would eat much of the brilliance. The larger the gem and the greater the saturation, the closer you want to get to the critical angle.
On large gems with deep saturation, cutting right on the critical angle is not only acceptable but actually desirable. As the gem is moved, you get flashes of brilliance mixed with windowing. This windowing allows the color of the gem to…
Donald Clark, CSM IMG
The late Donald Clark, CSM founded the International Gem Society in 1998. Donald started in the gem and jewelry industry in 1976. He received his formal gemology training from the Gemological Institute of America (GIA) and the American Society of Gemcutters (ASG). The letters “CSM” after his name stood for Certified Supreme Master Gemcutter, a designation of Wykoff’s ASG which has often been referred to as the doctorate of gem cutting. The American Society of Gemcutters only had 54 people reach this level. Along with dozens of articles for leading trade magazines, Donald authored the book “Modern Faceting, the Easy Way.”
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