The Ravage Addon makes working with multiple layers for materials a piece of cake. While there is another addon that looks similar at first sight, this addon had some interesting benefits. One benefit is that you can easily add a layer with your own node-group(s). I like this feature, because I am very familiar with the node-editor and that way I can use it in combination with my own addon. Another feature is that it is very easy to preview bakes for masks like pointiness, Ambient occlusion, Bevel and more.
And there is more: add a library with pbr textures, and also the possibility to load one albedo texture and derive bump map, roughness, etc from it. In short, it sounds like a complete solution to me, especially that you can add an empty layer with your own nodes. There is one thing: At the moment it supports only the channels: Albedo, Metallic, Roughness, Normal and Bump. But for 98% of the cases there is no need for more channels.
The addons comes with extensive documentation so it would be redundant to provide all the details here. What I want to provide is some info so you get the hang of the workflow a bit quicker. Very first thing is to save the .Blend file. Next, realize that you can make multiple layers and each layer can contain info for the channels: Albedo, Metallic, Roughness, Normal, and Bump.
Once you have two or more layers you can add a mask. With a mask you define where not the current layer got affected. This can be anything, for example: The first layer is plastic, the second paint. Then you add a mask to the second layer and you define that you don’t want paint on edges.
That is the very basic idea, but you can go all kind of directions. To name a few: you can paint the layer, you can mix albedo’s, or just roughness, or complete pbr materials. Or you can add a layer that only contains normals.
This menu is very handy. From the left to the right:
When you have your second layer, most likely you want to add a mask. But before you add a mask you will want to to bake a texture for that mask. So I suggest you to click on Bake, and then click a less obvious button called “Enable Bake Preview”. That will bring you to Cycles, Display render view. Now, select a UV-map, and choose one of the bake previews:
My favourite, if the geometry has enough polycount, is the Pointiness, otherwise Ambient Occlusion, Bevel or Thickness. After adjusting the settings of a map, you can bake it, disable bake preview (Go back to material preview, not the rendered preview), and then use it for a mask. For the mask try for sure the Edge Wear – Bevel Map. It has load of parameters to adjust the mask to your needs. (You can load/select the just baked map).
You can do this by adding a new layer, and then you click Black Layer. Then click Open Node Editor, and move your mousecursor in the node-editor and press TAB (this is an important step). You should now see as shown here below, if not then something went wrong.
Here you can add your own nodes, or if you have the Material Nodes addon for example, you can use it’s nodes in here. This is a huge pro of the addon, it means we are go all directions (for now as long as we use the Albedo, Metallic, Roughness, Normal and Bump channels).
You can download the Ravage Addon at Gumroad.
And you can find extensive (and awesome) documentation of the Ravage Addon on Github. Definitely take a look at it because there is much more the addon offers than I can describe here in this single-page article.