Volume Parameter Group

The Volume group contains parameters for describing the volumetric parameters of (partially) transparent materials.

Thin Walled

Name Thin Walled
Type Boolean
Range True or False
Usage Uniform Value only
Description When you select Thin Walled, transparent objects are treated as infinitely thin surfaces with no internal volume. When you disable Thin Walled, objects are treated as if they have internal volume. Transparent objects appear differently based on how light is bent, scattered, and absorbed within them.

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.

Examples

Index of Refraction

Name Index of Refraction
Type Decimal
Range [0..∞]
Usage Uniform Value only
Description The Index of Refraction (IOR) is a measured physical number usually in the range between 1 and 2 that determines how much the path of light bends, or refracts, when you specify a material for nonthin walled appearances. It also influences the reflection of light.

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.

Examples

Abbe Number

Name Abbe Number
Type Decimal
Range [0..∞]
Usage Uniform Value only
Description The Abbe Number quantifies the phenomenon known as dispersion in optics, in which the index of refraction depends on the wavelength of the light.

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.

Examples

Attenuation Color

Name Attenuation Color
Type RGB color
Range R: [0..255], G: [0..255], B: [0..255]
Usage Uniform Value only
Description The Attenuation Color is the color of light inside the volume of the object.

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.

Examples

Attenuation Distance

Name Attenuation Distance
Type Decimal
Range [0..∞]
Usage Uniform Value only
Description Attenuation Distance describes the density of the volume and impacts the intensity of the Attenuation Color. A value of 0 makes the surface opaque.

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

Examples

Subsurface Color

Name Subsurface Color
Type RGB color
Range R: [0..255], G: [0..255], B: [0..255]
Usage Uniform value only
Description Subsurface scattering (SSS) models the scattering of light inside a volume. Subsurface Color determines the overall color of an object after multiple scattering events.

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.

Examples

Subsurface Anisotropy

Name Subsurface Anisotropy
Type Decimal
Range [-1..1]
Usage Uniform Value only
Description Subsurface Anisotropy controls the direction of subsurface scattering, on a scale from -1 to 1.

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.

Examples