very easy way to make much more realisti cmaterials, is to use my "dirt map" material :)
it's a mixed material, you copy/paste opriginal mat into the other half of the mixed material, bingo! instant dirt ;)

I use it in nearly all my pics, it helps a ton. You can also cary ti's oclours for say, sun baked and worn etc

http://www.silverblades-suitcase.com/vue_mats/vue_materials.htm

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