Since my render tool was going to be ZBrush, I had to consider a few things before starting work.
Antialiasing is a critical issue. In order to have proper antialiasing in my final image, I had to keep in mind that I needed to render in twice as big a resolution and then shrink it to half later in post.
So, I created a new document with the required dimensions (2657x3636 pixels) and brought my ztool assembly into ZBrush. I activated Perspective mode and set the angle of the bust on the canvas according to my liking.
In order to save my view and avoid losing it in case of accidentally moving or rotating the camera (or in case of a crash), I opened the Document drop down menu, and then pressed ZApplink Properties > Cust1 > Save Views. In fact, by giving different names to the files I saved with Save Views, I was able to save as many different camera views as I liked, which is quite a handy tool indeed. (As an alternative method, I could have saved my ztool assembly as a .zbr document, converting my geometry to pixols and thus locking my camera view; then I could still modify my lights as much as I wanted, do detailing with stamps on the model, paint it with color and render it with materials.)
Next was the phase where I made my masks for use later in Photoshop, to crop off the several layers of rendered materials. With Flat render active, I selected one ztool at a time and rendered the same image over and over again, eventually getting a set of renders with different ztools depicted in pure white for each image (and all the rest in grey) ready to be used as masks.
After I was done with my masks, it was time to set up lights and get ready for the actual renders.
Talking about lights, the light rig I used for most of the materials - except the ones that already had specific lights information embedded - was a simple three point light rig (Fig.16).
For the rendering, I selected several MatCap materials, applied them each time on my model, and rendered them with Best Render. (Quite a few MatCaps though look better shadowed with Preview Render.)
The selection of the materials was done according to the type of renders I looked for, like diffuse, speculars, rim lights, cavity and so on (Fig.17 - 18). Of course, the same procedure was followed for every other angle of the bust.