I finished detailing the face, trying to push realism in the skin, eyes, hair and cloths. The next step was the hair. Here I used a gray color, and enhanced the lighter and darker shades of gray in his hair using different types of curly lines according to the reference images. I used the same process for the beard (Fig.19).
Now I painted on his skin. First I took a new layer for the skin texture and drew some small dots and curly lines (Fig.20). After completing some textures, I copied and pasted the same. Then I decreased the opacity of this layer, took the Stamp tool and used the texture over his head (Fig.20).
After that I used some bright light on his forehead and nose. Then I used a reference image for texturing purposes (Fig.21 - 22). I pit this image on a different layer and then placed it on top of the main painted layer (Fig.23).
I kept this texture on his lower face area, then selected this texture layer, selected Soft Light from layer properties and selected a layer opacity of around 25-30%. Then I selected the Eraser tool and the Airbrush Soft Round brush, and decreased some brush opacity from the top of the option bar (Fig.24). Then I lightly erased that texture on his head according to my requirements;, you can see how it was looking at this stage in Fig.25.
Here's the result after using textures with lights (Fig.26).
Next I started working on his clothes. First I finished doing the lights and shades; then I saved this work as a new PSD file, using a different name for my convenience. I used Corel Painter for creating the texture of his blazer. I could have used the same process as I used for the skin texturing, but I prefer using Corel Painter to get a realistic look for clothes - it's just personal preference.
So in Painter I opened that PSD file and took a new layer. I created a custom texture from the reference image and used it as a paper. I opened the reference image and selected it as a square shape (Selection tool) and then went to Window > Library Palettes > Show Papers (Fig.27).