This works pretty well provided you want all the segments in a RailClone object to have randomised materials. It's less successful if you need to add variety to only a single segment in a multi-part object. The basic procedure is as follows:
- Create a style with a new segment to take the randomised texture.
- Wire the segment to a Material node and set it to Randomise. The Range chosen will determine the number of variations.
- Create a new material and apply a Bercon Gradient or Multi-Texture map. For Bercon Gradient set the Type to Random and make sure the Randomise by Type is set to Material ID
For MultiTexture, set Randomise By type to Material ID
Alternatively you can use VizPark's Crossmap quite successfully with RailClone. This is very easy to use.
- Use Material IDs and create a multi/sub object material for each segment as normal
- Then use the CrossMap plugin for the material you wish to randomise ensuring you set the Image Distribution settings to V-Ray Instance.
- Despite the name, this seems to work for Mental Ray too!