The AbsorptionDefines how fast light is absorbed while passing through a medium. node defines how fast a medium absorbs light.
Density
Controls the absorption density. Higher values absorb more light (Figure 1).
Figure 1: Increasing the Density parameter
Volume Step Length
Applicable when rendering Volume mediums. The default value for the Step Length is 4 meters. If your volume is smaller, decrease the step length. Please note that decreasing this also reduces the render speed. Increasing this value causes the ray marching algorithm to take longer steps. If the Step Length exceeds the volume’s dimensions, then the ray marching algorithm takes a single step through the whole volume. To get the most accurate results, keep the Step Length is as small as possible.
Volume Shadow Ray Step Length
The step length that is used by the shadow ray for marching through volumes.
Absorption
Assigns a grayscale or color texture to the material to determine its absorption value. When using greyscale values, 0 (black) means that there is no absorption. Values greater than 0 determine how fast the medium absorbs white light (Figure 2).
Figure 2: Using a grayscale value to control absorption
You can also use color values to control Absorption. The observed color is the complementary color (opposite color) of the specified color value (Figure 3).
Figure 3: Using color values to determine absorption
Invert Absorption
Inverts the Absorption value, making the specified absorbed color the actual visible color.