I’ve had many questions about cutting garnets from new faceters. While my comments here are directed at garnet gemstones, the general principles I’m discussing apply to all highly color saturated gems.
Cutting Garnets Shallow
The color saturation of a gem is directly dependent on how long a distance light travels through it. This is the principle of selective absorption. 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 degrees.
Cutting Garnets On The Critical Angle
The angle for maximum brilliance of a colorless stone in this RI range would be 42 degrees. 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…