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VRayDirt 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.

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title UI Path: ||Material Editor window|| > Material/Map Browser ...	> Maps > V-Ray	> VRayDirt
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Radius – Determines the amount of area (in scene units) where the VRayDirt effect is produced. You can also use a texture to control the radius. The texture intensity is multiplied by the radius to calculate the final radius at a given surface point. If the texture is white at a given surface point, the full radius value is used. If the texture is black, a radius of 0of 0.0 is 0 is used.  For more information, see seeRadius Parameter example or the  or the Texmap Radius example example below.

Occluded color – – Specifies the color that will to be returned by the texture for occluded areas. You can also use a texture map for this parameter.

Unoccluded color – – Specifies the color that will to be returned by the texture for unoccluded areas. You can also use a texture map for this parameter.

Distribution – – 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. The Distribution parameter works with Inner occlusion, Ambient occlusion, and Ambient + inner occlusion modes. For ambient occlusion, set this parameter to 1to 1.0 to 0 to get distribution similar to the ambient lighting on a on a diffuse surface.  For more information, see the the Distribution Parameter example example below.

Falloff – – Controls the speed of the transition between occluded and unoccluded areas.  For more information, see the Falloff Parameter example below 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. Low Noise threshold values in the Image Sampler will clean the result further. For more information, see the the Subdivision Parameter example below.

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. Consider that these parameter parameters can also take negative values for inverting the direction of the effect. For more information, see the the Bias example below.

Affect alpha – When enabled, the texture automatically receives an alpha component from the generated dirt distribution and this way makes the unoccluded area of the VRayDirt map transparent. When disabled, the alpha values from the maps used in Occluded and Unoccluded color slots are applied. 

Ignore for GI – When enabled, Determines whether Ignores the dirt effect will be taken into consideration for in GI calculations or not . For more information, see Ignore for GI example belowexample below.

Ignore bump – Excludes bump maps from VRayDirt computations. The option is useful, when the bump effect is too strong and may produce undesirable effects such as holes. For more information, see Ignore bump example below.

Ignore self occlusion – When enabled, the object does not occlude itself. It is occluded only by other objects in the scene.

Consider same object only – When enabled, the dirt will affect affects only the objects themselves, without including contact surfaces and edges. If off, the entire scene geometry is participating for the final result. For more information, see Consider Same Object Only example below below.

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

Work with transparency – Ignore invisible objects – When enabled, VRayDirt will take 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 (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.

Environment occlusion – When enabled, V-Ray will use the environment when calculating the occlusion of areas that are not occluded by other objectsIncludes environment contribution to the shading of unoccluded areas.

Thin mode – Enhances the look of thin surfaces by casting less dirt on them. It is available only for Inner occlusion mode. For more information, see Thin mode example below.

Mode – Specifies the mode in which the dirt map is going to be calculated.

Ambient occlusion – Normal ambient occlusion will be is calculated.
Reflection occlusion (Phong, Blinn, Ward)  –  – Reflection occlusion will be is 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 Inverts 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. For more information, see Inner Occlusion example below below.
Ambient + inner occlusion – A combination of Ambient occlusion and Inner occlusion modes used for enhanced weathering effect.

Streaks ambient – Draws streaks across dirt effect respective to ambient occlusion. For more information, see the Streak Ambient example below.

Streaks inner – Draws streaks across dirt effect respective to inner occlusion.

Streaks blur – Gives ability to blur the streaks. Bare in mind that new algorithm is calculating this effect, and the visual representation of the streaks is different. For more information, see the Streak Blur example below.

Blur – Controls the amount of the blur of the streaks.

Streaks size – Controls the thickness of all streaks. For more information, see the Streak Size example below.

Streaks density – Controls the density of the streaks. For more information, see the Streak Density example below.

Reflection glossiness –  Controls  – 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 cause multiple rays to be traced in the approximate reflection direction.

Affect reflection elements  – When enabled, the ambient reflection will affect affects the reflection render elements. This can be used to create reflection mask.

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

Result AffectAffected by – Specifies a list of objects which will that affect the calculation of the VRayDirt map. Excluded objects will be are considered "invisible" for the calculations of the VRayDirt map - they don't produce the effect over other objects.

Example: Ignore for GI

This check-box determines whether When Ignore for GI is enabled, the dirt effect is going to be visible doesn't contribute to the global illumination and so it's invisible during the GI calculation. Note that the examples show the calculation of the GI (during Light cache calculations), hence the noise.

The 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.