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With scattering medium you can simulate particle scattering to create such effects as fog or smoke or volumetric lighting such as visualizing beams or rays of light.
Applying Scattering Medium
In the Project window, Material tab, select Scattering Medium from the Type dropdown menu. Textures can be assigned to the Density Texture in the Textures tab. OpenVDB files can be loaded by selecting Volume Map from the Texture dropdown or via the Material Graph and applying it to Density Texture on the Scattering Medium material node.
Adjusting Scattering medium
This option controls the overall color of this material type. When light enters the surface it will take on the color set here. The amount of color that you see in this material is highly dependent on the color density setting as well. If you have set a color in the transmission, but it looks too faint, skip down to the color density section.
This slider controls the depth of the color selected in the Transmission setting, depending on the thickness of the part to which the material is applied. Use Transparency Distance to make the Transmission color more or less saturated and prominent. A lower setting will show the color more in thin areas of the model, and a high setting will make the color faint in the thin areas.
Determines how close the particles are - High Density values will make the scattering medium seem more solid, where a low density
When checked the rays will bounce multiple times inside the geometry. This will create a more physically correct representation of the material, but it affects the processing time.
Albedo is the color of the light scattered by small particles inside the scattering medium. Note, that in media with Multiple Scattering the color of the medium may be the inverse of the albedo color, since the scattering process can prevent light from reaching the observer as it travels through the medium.
Controls how the light is scattered. A value of 0 is uniform scattering, a negative value will scatter light backwards, a positive value with scatter light forwards.
A low samples setting (8 or lower) will tend to make the surface look more noisy, which will give a more imperfect and rough look. As you increase the value, the noise will even out more and provide a more evenly distributed roughness.
The density texture will act as a sort of mask on the material - where the texture is black, no particles will be shown and the amount of particles will increase where the texture is lighter. To use VDB filed on the density texture, add a Volume Map.
With labels you can add another material onto the surface of the scattering medium. Control the label with the 4 primary Map Types - Diffuse, Specular, Bump and Opacity. - just make sure to add an opacity map when using a label - otherwise you won't be able to see the scattering medium.
Caustics work inherently with volumes (e.g. scattering media), however, caustics will only be applied to light sources outside the volume and this is only supported with interior mode.
Scattering medium with a Volume map applied to the Density texture.