The videos below (one for mental ray, one for V-Ray) show how to use RichDirt to create a very good looking dirt Render Element.
If you are familiar with compositing, in your favorite composite software, or Autodesk Composite,
or Adobe Photoshop this tutorial will show you how to massivly gain time.
It describes a setup that needs just 2 minutes, to weather an arbitrary building. It also shows clearly what advantages the ´optimize thin´ parameter has when you work on a whole building with render elements.
Note: you can watch the video in HD - press the ´YouTube´ button, and then on YouTube use the 720p option (found right of the timebar).
the same tutorial, using mrShader Element
On mobile devices the screen can be small. Click the links below to get full size YouTube. You could also run the video above, and press the full screen [ ] symbol on the lower right part.Full Size VRay YouTube
Full Size mental ray YouTube
RichScene versus Render Elements - what is better If you are used to Render Elements and have your full pipeline based on compositing you might not need the new RichScene plugin. RichScene changes materials in the scene - it adds RichDirt to the diffuse slot of all materials. This is much faster for everbody that doesnt have a compositing pipeline. It also allows more control, different parts of the scene can get different dirt. Last but not least - dirt is then also visible in reflections and with global illumination. For example a rusty brown area would do color bleeding in Final Gather (mental ray) or Light Cache (V-Ray).