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Occluded color – Specifies the color that is returned by the texture for occluded areas (areas where a surface's ambient lighting is limited or blocked). A texture map may be used for this parameter.

Unoccluded color – Specifies the color that is returned by the texture for unoccluded areas (areas where a surface is fully exposed to ambient light). A texture map may be used for this parameter.

Radius – Determines the amount of area (in scene units) where the VRayDirt effect VRayDirt effect is produced. A texture can be used to control the radius. For more information, see the Radius example below. 

Distribution – Forces the rays to gather closer to the surface normal. This results in the dirt area narrowing closer to the contact edges. Allows values between -100.000 and 100.000. For ambient occlusion, set this parameter to 1.0 to get distribution similar to the ambient lighting on a diffuse surface. For more information, see the Distribution Parameter example below.

Falloff – Controls the speed of the transition between occluded and unoccluded areas. For more information, see the Falloff example below.

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. This parameter works independently from the Use Local Subdivs parameter in the DMC Sampler, so changes affect the scene even if Use local subdivs is disabled. Low Noise threshold values in the Image Sampler clean the result further. For more information, see the Subdivs example below.  

Directional Bias (X,Y,Z) – Biases the normals to the X (Y,Z) axes so that the dirt effect is forced to those directions. Consider that these parameters can also take negative values for inverting the direction of the effect. For more information, see the Direct Biases example below.

Ignore For Gi – Determines whether the dirt effect is taken into consideration for GI calculations or not. For more information, see the Ignore for GI/Consider Same Object Only example below.

Consider Same Object Only – When enabled, the dirt affects only the objects themselves without including contact surfaces and edges. When disabled, the entire scene geometry participates in the final result. For more information, see the Consider Same Object Only example below.

Double Sided – When enabled, the rays needed to generate the dirt map are shot from both sides of the faces (both in the direction of the normals and in the opposite direction).

Invert Normal – Changes the direction of tracing the rays. When disabled, the rays are traced outside the surface; when enabled they are traced inside the surface. This allows us to revert the effect with respect to surface normals - e.g. instead of crevices, open corners are shaded with the occluded color. For more information, see the Invert Normal example below.

Ignore Invisible Objects  – When enabled, VRayDirt takes 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 disabled (the 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, the object does not occlude itself. It is occluded only by other objects in the scene.

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

Occlusion Mode – Specifies the mode in which the dirt map is calculated.

Ambient occlusion – Normal ambient occlusion is calculated.
Reflection occlusion (Phong, Blinn, Ward) – Uses reflection occlusion. 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). 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.

Affect Reflection Elements – When enabled, the ambient reflection affects the reflection render elements. This can be used to create reflection masks.

Glossiness – Controls the spread of the rays traced for reflection occlusion. A value of 1 means that just a single ray is traced (just like when tracing clear reflections), smaller values make the spread of the traced rays.

Affected By –  Specifies a list of objects which are affected by the calculation of the VRayDirt map. Excluded objects are considered "invisible" for the calculations of the VRayDirt map - they don't produce the effect over other objects.

As inclusive set – Controls the meaning of the Affect By option. When enabled the Affect By is considered as an "Include list", and when disabled the Affect by is considered as "Exclude list".

Exclude –  Allows you to disable the calculation of the VRayDirt map for specific objects. Excluded object are not shaded by the VRayDirt map.

As Inclusive list – When enabled, reverses the meaning of the Exclude list, and only objects in the list will be shaded by the VRayDirt map.