Material and Render setup:

Back in Maya, I imported an eye Substance texture provided with the Substance library in Maya and started tweaking it. Then I created another Substance node in the "Node Editor", loaded my skin material and customized it in the same way.

I split my graph in SD in order to smartly feed the nine maps, and I created 16 parameters that I can now use in order to dynamically customize my texture without having to go back and forth between Maya and SD if I want to adjust some details.

Pre-visualization stage has come to an end, let's now focus on serious business and start the rendering process using sub-surface scattering, ray-tracing and so on... I began to set up a simplified studio light rig by using two mentalRay Area lights as key and rim lights.

I also created a mentalRay Physical sun & sky that I plugged to an environment shader used with an "mib_blackbody" and a portal light. The environment is only composed of a polysphere with reversed normals and the default Maya Lambert shader assigned to it.

I started to make some test renders in order to see how the light rig interacts with the overall environment, then I moved on to the shading setup for the head model.

I enabled all the outputs and used Substance Bonus Tools for Maya(Windows, OSX) in order to link the outputs to temporary bitmap files that will render without any problem with mentalRay.

The skin material is composed of a "misss_fast_skin_maya" shader in which I plugged the Overall color, Back Scatter, Subdermal, Epidermal and Diffuse textures. Then I plugged the sss shader to an "mia_material_x_passes", in addition to this, the Normal map, Reflection, Gloss, Roughness and Displacement map extracted from Mudbox were also connected to the mia shader.

In order to properly use displacement with mentalRay I needed to select my mesh go to "Window->Rendering Editors->mental ray->Approximation Editor" and add subdivision levels to our head, in this case I chose a value of 3 for the "N Subdivisions" parameter.

I started to do some test renders where I can adjust the shader settings, lights intensity or the substance material. I have also started to create multiple render layers where I isolated the head with only the rim light, key light and so on... It will give me much more control during the compositing stage. I don't really mind the glitches on top of the head because I did not focused on this part of the head in Mudbox, and it will soon be hidden by the hair anyway...