I am making a model of an old worn machine, and I want the recesses of it to be less shiny than the open, flatter surfaces of it, and also for the recesses to be dirtier, as if the people that clean it can only be bothered to give it a quick scrub in the easy-to-get-to surfaces and can’t be bothered to get a small brush and scrub in the recesses too.
It struck me that the areas least likely to receive a scrub are the same areas light finds it harder to reach. So, I thought of using the Cycles Ambient Occlusion shader to designate between shiny open surface and grubby recesses. Instead of shading to black, shading to the colour of the dirt and also using it to effect the glossy.
However, I cannot get it to to work. I cannot even get the Ambient Occlusion shader to show any signs of itself even in normal use. Can anyone help me with this? Do you need to activate ambient occlusion elsewhere apart from the shader?
The AO Shader doesn’t work in the same way you might get from baking AO to a mesh’s uv image. You can use the texture atlas addon to bake AO to a uv image to use like this, plugged into the mix factor, or you can use Dirty Vertex Paint layer named in an Attribute node plugged into the mix factor.
You need enough geo to make use of the dirty vertex paint to begin with. I start with the header Paint>Dirty Vertex Colors, and hten use the highlight angle and dirt angle and blur iterations to dial in what I want. You can then make some paint with the brush tools to accent or contrast areas.
Just remember, if you need to you can bake it in BI to a texture and us it in other ways. You can also use a color mix node after it to multiply it with the second color input before it goes to the fac input of the mix shader node, and you can plug it directly into a diffuse node to see it in cycles preview.
