Specular Channel
For the specular channel, we want the smooth parts of the object to have stronger highlights than the rest. We can do this by setting the overall value of the specular channel to zero, and then using a "Value" procedural set to 100% masked by a gradient responding to the "Smooth" weightmap.
To add to the realism we can add a Turbulence procedural to add texture to the highlights. Adding this sort of detail to the specularity channel is one of the best ways to make a surface look real.
In the end, I set the Value procedural to 120% in order to boost the highlights further. The "Colour Highlights" parameter on the "Advanced" tab was set to 70% in preparation for creating the colour channel. For details on the other parameters, download the finished object at the end of this tutorial.
Colour Channel
To colour the anvil, I used these four components in the colour channel (in order from bottom layer to top):
- Base Colour - The main colour of the anvil (set in the main surface properties dialog), set to RGB = (81,70,68)
- Smooth Colour - A "Value" procedural RGB = (141,132,126) masked by a gradient responding to the "Smooth" weightmap. Places colour highlights along the smooth parts.
- Fractal Noise - A "Turbulence" procedural set to black at 50% opacity to add some dirt and noise to the colour channel.
- Slope Based Rust - A gradient that places orange hilights on a particular gradient of slope. This is then masked by another gradient to make sure it only applies to the bottom section of the anvil.
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| Base Colour | Smooth Colour | Fractal Noise | Slope Based Rust |
The four pictures above show how the colour changes as each component is added in turn. The picture below shows the colour channel mixed with the bump and specular channels.
More 3D Graphics: 
