Gem

The Gem Appearance Type is a version of Glass that is optimized for gemstones.

Parameters

Solid Switches between two-sided verses and one-sided properties.
Color Sets the color of the appearance in diffuse white light.
IOR (Index of Refraction) Controls how appearances with transparency bend light passing through them. It indirectly affects reflectivity. When using a surface without thickness, the IOR affects the reflectivity of the surface, but the light passing through it will not refract. On a surface with thickness, this appearance causes light to refract as it passes through the Solid object.
Color Density Determines the density of the color on the simulated surface, compared to solid glass in reality.
This parameter is dependent on the size of the part it is mapped onto. You may need to adjust the value to match the size of the actual part it is being mapped onto.
Roughness Controls the highlight size in reflected light. The rougher the appearance, the more it diffuses the highlight (the larger and less focused the highlight becomes), such as with frosted glass.
Abbe Number Sets a fixed color for the appearance. This color does not change regardless of the light falling on the appearance (the appearance is not shaded).