anyone have a good idea how to create dirty glass?

[emmanuel_shiu]

I've tried looking through as many youtibe tutorials as I can and can't seem to be able to find a good way to create a dirty glass that looks like this. I've tried using custom maps for the refraction glossiness but it just doesnt look right and very hard to control. anyone have any ideas?Thanks!

[fixeighted]

You could map opacity with a suitable grunge map, mixed with a radial gradient with some noise in that gradient.
That on a plane which is offset slightly from each glass piece gets something like the attached result.

[SonyBoy]

A map on the reflection roughness should be all you need to achieve this kind of effect. Combine that map with some color variation and/or to drive a dirt layer and it should get you there. Although technically it's possible to map refraction roughness, I've never found this to be practically useful. SFAIK, refractivity is not a volumetric calculation, so there's no point trying to use something like a 3D texture either which would in any case be extremely expensive to render.

[vladimir_krastev]

Hi, for a better final result you may want to combine a few things. The reflection/refraction of the base material (the glass) is the first step. On top of that it would be nice to have the dirt/grease as separate layers in a VRayBlendMtl for instance.