Now it's up to you to decide if there is going to be shine and how much. But only the paint should shine - not the rust.

So I define a new variable, paint, that is the opposite of rust. (1 - rust) This is my paint map.

I use the paint map to control the Blinn. Now there is no shine in the rust area.

p = Clouds(0, 1, Scale=.5, Complexity = 5)
t = .5
rust = Clamp(200 * (p - t))
paint = 1 - rust

paintColor = IColor(80, 103, 119)
rustColor = IColor(90, 30, 24)
color = Blend(paintColor, rustColor, rust)
diffuse = Diffuse(color, .8)

surface = View(diffuse)

s = .3
bubble = Clamp( (p-s) / (t - s) ) - rust
surface.Displacement = .03 * bubble

surface.Alternate_Specular = Blinn(1, .1, .4 * paint)

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Renderosity forum reply notifications are wonky. If I read a follow-up in a thread, but I don't myself reply, then notifications no longer happen AT ALL on that thread. So if I seem to be ignoring a question, that's why. (Updated September 23, 2019)