I thought we were taking about the car paint. Add some noise as I mentioned before. Use it on the diffcuse channel to affect the color, but also add the same noise to the reflection channel, to modulate how much reflection there is on the noisy parts. They should be less reflective. Make sure to scale up the noise, so it resembles dirt. Try and see if you can add a falloff to the txture, so it's mostly visible near the ground and then disappears as you get higher up.
Exactly, fresnel effect is the key to get realistic reflections on almost all kinds of surfaces. (maybe dielectrics, metals, have refl. IOR so high that it is common to cheat here by turning the fresnel off and get nice and supershiny chrome)
Dude who knows everything about 3D deep inside, doesn't use Max, but is an expert in Mental Ray, and says "shader"..... SOFTIMAGE? :cyclops:
Boekanier, I had a look at your V-Ray material, and it seems to be an okay basic car paint, fresnel on, can't see anything which could create that funny unrealistic reflection on your Vectra near the camera... are you sure it is the material we see rendered at your other picture?? I am confused and I think I know V-Ray.
That latest render features V-Ray Dirt? I am not a big fan of it, never got any realistic output. I believe that using some good B/W dirt textures and ofc playing with mapping will bring the effect you want. Instead of this rather computerish gradient which reminds me of Eric's ugly faked GI shadows I so hate on LFS screenshots, lol.
A tip: try Vray blend material for that - it allows you to keep your current materials and easily tune dirt material on top of it.
But please easy on dirting your garage!
I love your steep learning curve, from 1st to last renders I can see a great advance! Some very nice renders mate, keep it up and we become colegues in business one day.