As you can see from the intervening posts, I’ve progressed quite a ways in the texturing of my robot, but I’m going to stick to just talking about the head for now. Upon review of my concept description, I saw that I had missed a bit of detail: oxidation on the sun-exposed areas. My previous textures were either taken from various places on the Internet or painted by hand. My oxidation texture is from some photographic reference I shot myself. Since I have full rights in this texture, I’ll post it here at full resolution. This image carries a Creative Commons Attribution 3.0 License 
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“Oxidized Paint Texture” by Bryan Ray is licensed under a Creative Commons Attribution 3.0 Unported License.
Permissions beyond the scope of this license may be available from xa_bryan@sbcglobal.net
I defined a new pattern with this texture and flood filled an entire layer with it, then put a completely black layer mask on it. Then I used a large soft brush to paint white on the mask where I wanted the texture to show up, notably on the top-facing surfaces of the head. I then added an adjustment layer and copied the mask information onto it so I could integrate the oxidation better with the rest of the paint. A little tweaking of the opacity finished that process, and now it’s time for the bump map.
Some people simply desaturate their color map and use that as a bump, but that is certainly the wrong way to go about things with this texture. For instance, the flaked off paint is white, but white is high in a bump map, so the scratches need to be inverted. Once that’s done, they’ll probably be far too dark, and therefore too deep in the bump; that can be fixed by adjusting their opacity. Since the scratches are taking their height information from the scratch layer, there is no need for the layer mask on the paint layer, so that gets deleted. Finally, I sharpen the oxidation layer a bit and adjust its opacity so that the variation is a little bit less than that of the scratches.
I mentioned earlier that I was going to put a little bit of a ridge on the nose cone to help disguise a seam, so I painted that in by hand; you can see it in the lower right-hand corner. Also, I adjusted the levels on the weld a bit to get it that ridged look.
Some bits of elevation are more dramatic than can be handled by a bump map. In this case, the weld doesn’t pop up enough. Unlike other maps, there isn’t an obvious place to insert a displacement map, so I do it through the Hypershade. First, here’s the map, and as before the lighter areas are higher:
I open the Hypershade (Window > Rendering Editors > Hypershade), find my HeadM material and middle-mouse drag it into the lower pane. Then I make a new file texture, load the displacement map, and middle-mouse drag the texture onto the material. In the pop-up, I choose Displacement Map. A new Displacement node is automatically added between the file and the ShaderGroup node. Unlike the Bump Map node, though, the Displacement node has no useful controls. If you need to adjust the depth of the displacement (and you almost certainly will), the simplest way I know of to do it is to load the file node in the Attribute Editor and adjust the Alpha Gain under Color Balance. In this case, I had to take the Alpha Gain clear down to .02 to get this, which has some visible problems:
It took some experimentation, but I figured out that some of the problem was the lack of resolution in my mesh. I added two levels of divisions and rerendered to get this:
This introduces some unwelcome faceting of the mesh, but it closes up those odd seams and smooths out the ridges in the displacement.
You can also see here that I’ve added the glowing lights by saving them to a file of their own which I added to both the incandescence and glow intensity channels. An adjustment of the alpha gain of the file controls the amount of glow that appears. Mine is currently set at .08.
That’s about as far as I’ll take the head texturing, but I can now use the Photoshop file to set up for all of the rest of the robot. Since most of the details will be similar, I can keep my layer structure, brushes, and colors. I simply save a copy of the file under the name TextureTemplate. In the new file, I erase all of the details I’ve painted in, leaving only the base colors and solid masks, so the file is ready to receive a new UV layout and ambient occlusion map. Since everything is set up in this way, further texturing tasks go much more swiftly.
