I knew there would be trouble when you asked for three different topics in one thread.

You asked about procedural wood - that was one topic.

You asked about rust - that was antoher topic.

Later, you asked for dust - that was third topic.

These three topics each need a unique shader. Each has nothing whatsoever to do with the other. They would share no ideas at all.

You asked about Clouds while quoting me about dust. Look above - the quote is about dust, then you say "would I use clouds for this." No you would use clouds for rust, not dust. One has nothing to do with the other.

There is something UNDER the dust. Whatever that is, imagine it comes out of one node, like my VSS skins shader does. That one node must represent the material UNDER the dust, and has nothing to do with the dust.

Whatever that node is, you need to Blend that with a white Diffuse node, with the amount of blending driven an N node to decide if it is facing up or down.

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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)