And finally, the diffuse map (Fig.19).
The original size was 4096 x 4096 (Fig.20).
One cool thing about painting an old dude's skin is that you can go pretty far in detailing without being unrealistic. It would have required more finesse to make a young lady, for example.
The bump channel, as I explained earlier is easy to make, since it's already made (see Fig.11). I used this map to paint the specular channel.
In Photoshop, I used the bump map as a background, then added the displace map in Multiply mode on top of it with an opacity of around 60%. Using displace is optional as bump alone can give good results, but if you use both, you'll have wrinkles (displace) and fine details (bump) as a basis for painting the specular channel.
Next I turned the luminosity to something near to dark gray (Fig.21), then into a new layer I start painting white zones where I wanted highlights and specularity (mostly cheeks, chin, lips, upper head)(Fig.22).