Dirt

Dirt is a texture map that can be used to simulate a variety of effects. For example: dirt around the crevices of an object, or to produce an ambient occlusion pass.

UI Path: ||V-Ray Node Editor|| > Shader > Add > Textures > V-Ray Dirt

This section describes the input sockets of the node. Some sockets have dedicated parameters, which are further described below, and some sockets are just inputs.

Unoccluded Color (input socket) – Allows a color node to serve as the Unoccluded Color parameter.

Occluded Color (input socket) – Allows a color node to serve as the Occluded Color parameter.

Radius – Allows an integer-outputting node to serve as the Radius parameter.

Glossiness – Allows an integer-outputting node to serve as the Glossiness parameter.

Occlusion Mode - Allows you to specify the mode in which the dirt map is going to be calculated. 

Ambient occlusion - Normal ambient occlusion will be calculated.
Reflection occlusion (Phong, Blinn, Ward) - Reflection occlusion will be used. The difference between ambient and reflection occlusion is basically in the direction in which rays are traced. With ambient occlusion, rays are traced in all directions uniformly, while with reflection occlusion, the direction depends on the viewing direction (just as when calculating reflections), and the spread of the rays depends on the Reflection glossiness and BRDF type used. 
Inner occlusion – Allows the user to invert the effect with respect to surface normals - e.g. instead of crevices, open corners are shaded with the occluded color. This mode changes the direction of tracing the rays. When this mode is selected, the rays are traced inside the surface, otherwise, they are traced outside the surface.
Ambient + inner occlusion – A combination of Ambient Occlusion and Inner Occlusion modes used for enhanced weathering effect.

Occluded Color – Specifies the color that is returned by the texture for occluded areas. If a texture is selected, it overrides the color as long as the texture checkbox is enabled.

Unoccluded Color – Specifies the color that is returned by the texture for unoccluded areas. If a texture is selected, it overrides the color as long as the texture checkbox is enabled.

Radius – Specifies the amount of area (in scene units) where the Dirt effect is produced. If a texture is also used, the Radius value determines the amount of area where the texture blends.

Distribution - This parameter forces the rays to gather closer to the surface normal. The effect is that the dirt area is being narrowed closer to the contact edges. For ambient occlusion, set this parameter to 1.0 to get distribution similar to the ambient lighting on a diffuse surface. 

Falloff - Controls the speed of the transition between occluded and unoccluded areas.

Subdivs - Controls the number of samples that V-Ray takes to calculate the dirt effect. Lower values render faster but produce a more noisy result.

Bias

Bias X/Y/Z - These parameters will bias the normals to the (X, Y, Z) axes so that the dirt effect is forced to those directions. These parameters can also take negative values for inverting the direction of the effect. 

Streaks

Ambient Streaks – Draws streaks across dirt effect respective to ambient occlusion. Note that a bias direction and value have to be specified for the streaks to appear. 

Inner Streaks – Draws streaks across dirt effect respective to inner occlusion. Note that a bias direction and value have to be specified for the streaks to appear.

Streaks Blur – Blurs the streaks. Bear in mind that a new algorithm is calculating this effect, and the visual representation of the streaks is different.

Streaks Size – Controls the thickness of all streaks.

Streaks Density – Controls the density of the streaks. Streak density is currently not supported on V-Ray GPU.

Blur – Controls the amount of blur of the streaks. Blur is currently not supported on V-Ray GPU.

Thin Mode – Enhances the look of thin surfaces by casting less dirt on them. It is available only for Inner occlusion mode.

Ignore For GI - Determines whether the dirt effect will be taken into consideration for GI calculations or not. 

Ignore Bump – Excludes bump maps from Dirt computations. The option is useful, when the bump effect is too strong and may produce undesirable effects such as holes.

Consider Same Object Only - Determines whether additional geometry in the scene is considered when calculating the dirt effect, including contact surfaces and edges.

Double Sided - When enabled, rays will be traced both in the direction of the normal and in the opposite direction. This creates an effect where both crevices and edges are occluded. 

Ignore Invisible Objects – When on, VRayDirt will take into account the opacity of the occluding objects. This can be used, for example, if you want to calculate ambient occlusion from opacity-mapped trees etc. When off (by default), occluding objects are always assumed to be opaque. Note that working with correct opacity is slower since, in that case, VRayDirt must examine and evaluate the material on the occluding objects. 

Ignore Self Occlusion - When enabled, objects will not be able to occlude themselves. 

Environment Occlusion - When enabled, V-Ray will use the environment when calculating the occlusion of areas that are not occluded by other objects. 

Affect Reflection Elements - When enabled, the ambient reflection will affect the reflection render elements. This can be used to create reflection mask. 

Glossiness – Controls the spread of the rays traced for reflection occlusion. This is only used in Phong, Blinn, or Ward ambient occlusion mode.

Include – When enabled reverses the meaning of the Exclude list - only objects from the list will be shaded by the dirt map.

Object – Adds objects to the Exclude list. Objects in the list are not affected by the dirt map.

Include – When enabled reverses the result from "Affected By" list - the objects from the list will shade other objects with the dirt map.

Objects – Adds objects to the Affected By list. They can either be Included or Excluded from the Dirt calculations, depending on the Mode.

Collection – Add collections to the Affected By list. They can either be Included or Excluded from the Dirt calculations, depending on the Mode.