I'd like to overlay dirt to a texture using material nodes. Problem is, I'm "challenged" in there! My immediate need is to apply smudges to V3 to dirty her up a bit but I'd also like to be able to adjust the size and randomness of the smudges. In the longer term, I could also use material nodes to "dirty up" other objects such as building walls. Does anyone have any tips to accomplish this?

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thanks all. Not sure how I missed the thread during a search ... oh yes I am. :-)

To change the size of the dirty patches, adjust the scale of the clouds node. Raise Value_1 of the Math_Functions node to increase the coverage of dirt and lower it to decrease the dirt. Value_1 of Math_Functions multiplied by Value_1 of Math_Functions_2 should be equal to 1.

Whoa Ajax. Now that's some dirt. You must be the savant that can "see" math functions. :-)

Well I wouldn't call myself a savant, but I have a degree in mathematics and I work in a related field, so yeah, I can often visualize what this stuff is doing in my minds eye. This one is a quick and dirty (no pun intended) job, so there's not too much going on mathematically speaking in this shader. I'm just blending some random patches of rough dirt onto the skin. It actually looks more like she's been burned, doesn't it? I should probably run the dirt through a colour ramp to stop it being jet black and I should lift the dirt bumps a little as well - there are some places where it kind of looks like the dirt is carved out of her instead of sitting on top of the skin. I was basically just trying to show how you blend a dull bumpy surface with something that's a little smoother and shinier. Hope it helps :-)