Volume Parameter Group

Thin Walled objects are much faster to render. Windows, for example, are usually very well approximated with a thin walled material, as the glass is very thin and refraction is hardly noticeable. Parameters such as Attenuation Color, Attenuation Distance, Subsurface Color, and Subsurface Anisotropy do not affect the appearance of objects when you enable Thin Walled since they apply to how light behaves inside an object.

Set the Index of Refraction value based on the object's material. You can research the Index of Refraction for any material online. For instance, the Index of Refraction values for water, window glass, and diamond are 1.33, 1.52, and 2.42 respectively.

Typical values for the Abbe Number range from 20 (flint glass) to 60 (crown glass). The larger the Abbe Number, the weaker the effect. Use this parameter when rendering gem stones.

If you specify 1 for Transparency, it may seem you can control the color of the appearance with both, Albedo and Attenuation Color. There is a subtle distinction between the two parameters. Albedo controls the light on the outer surface, while the Attenuation Color determines what happens within the volume. As a guideline, if an object is thin walled, specify its color using Albedo. For volumetric objects, use the Attenuation Color and Attenuation Distance parameters.

This parameter is dependent on the size of the object. You may need to adjust the value accordingly.

To achieve effective subsurface scattering, consider these parameter settings: Start with a white Albedo, full Transparency, a small Attenuation Distance, and a somewhat grayish value for Attenuation Color. When selecting a Subsurface Color at this point, it will closely resemble a pure diffuse object with the same color set as the Albedo.

Values less than 0 produce backward scattering, while values greater than 0 produce forward scattering. When you set the value to 0, scattering occurs in all directions equally.