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Make materials appear more realistic by quickly adding detailed weathering and dirt effects to your materials without UVW mapping.
Downloads
If you would like access to the scene files used in this tutorial please click here to download.
Dirt and weathered effects can improve the overall look and feel of the materials within your scene. However when you are using procedural materials such as metals and plastics you might not have UVW mapping. By using VRayDirt you can add these effects without the need for UVW mapping as it is done using procedural techniques. Very quickly you can build up dirt and blend as many layers as you wish to greater improve the look and feel.
Start by opening t_Q&A_168_Vray_Start.max and select the group named “Water Hydrant”. In the material editor select an empty material slot and apply it to the group selected. Add a VRayCompTex to the diffuse slot, this texture map will allow us to blend the two dirt effects into one material. In Source A, add VRayDirt and you will be presented with a range of parameters for adjusting the material.
The dirt effect will start from crevices and spread until it reaches the set radius
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By default the dirt spreads equally at crevices until it reaches the maximum radius. The larger the radius, the further the dirt spreads from its origin so set the radius to 100mm.
The occluded colour will be where the dirt is present and the unoccluded colour will be where the dirt is not. Set the diffuse for the occluded colour to R6 G2 B1. The distribution and falloff parameters affect how the dirt appears within the set radius. For example you can make the dirt more apparent closer to the origin but for this tutorial the default settings are suitable.
Much like everything else in V-Ray, the quality of the dirt is controlled by the number of subdivisions, set this to 32 to increase the quality and reduce noise.
Control the dirt distribution by using noise maps
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In the radius maps rollout, add a noise map and set the size to 1.0. This will affect how the dirt is distributed within the set radius. The noise map colours are black and white so the dirt will appear at zero size where there are black areas and at full size at white areas. A mid grey colour would mean the dirt is at half size. Click on go to parent and add a splat map to the unoccluded colour and set the size to 10. Set the first colour to R68 G0 B0 and the second colour to R36 G2 B2. This will be the diffuse colour of the material.
The minimum blend mode means the darkest RGB values are blended together ignoring the brighter pixels
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Click on go to parent twice and Copy the VRayDirt material from source A of the VRayCompTex and paste a copy into Source B. In the operator dropdown box choose Minimum (Min{A,B}). This will combine the two texture maps by their darkest RGB colour.
The bias parameter controls the direction of the dirt will travel from its origin
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Within Source B, set the Y and Z bias to 5.0 to force the dirt in a non-uniform direction but leave X at 0.0. Tick the box for invert normal. By using the VRayCompTex you are combining dirt that will appear in dark corners and crevices as well as dirt that travels along open faces in a downward direction.
Use VRayDirt to control reflection strength
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Click on go to parent twice to go back to the top level of the material and copy the VRayCompTex from the diffuse map slot and paste it in the reflect map slot. For both sources A and B in reflection set the occluded colour to R0 G0 B0 and the unoccluded colour to R75 G71 B59. This will make any area where the dirt is present non-reflective. Finally remove the splat map. Click go to parent twice to go back to the top level and set the reflection glossiness to 0.85 and set the subdivisions to 32. Turn Fresnel on and set the Fresnel IOR to 3.0. Scroll down to BDRF parameters and choose Ward from the drop down list as this type is used for metallic reflections. Finally in the bump map slot add a noise map and set the size to 0.7.
Quick Tips
Setting the size of VRayDirt
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Using a large radius for smaller objects may cause surfaces to render completely occluded so set your radius proportionate to the size of the object by using separate materials per object.
Exclude objects from influencing VRayDirt
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If multiple objects are intersecting the VRayDirt material you may wish to stop some if not all of them from contributing to the dirt effect. Use the exclude or consider same object only options to do this.
Make dirt visible through transparent objects
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By default the VRayDirt is not set up to work with transparent objects such as glass. Tick work with transparency in the settings in order to generate get accurate occlusion.