These are monochromatic umber underpainting exercises. Basically the beginning stage of a portrait or other type of painting but I use them as ways to better develop my realistic rendering to avoid the natural bend to exaggerate as in a caricature. Sometime down the road I may add color to these but for the moment this was the desired end result.
This one took about an hour, three twenty minute sessions, of careful measuring and rendering.
This one about 40 minutes.
The lighter ones to the left are two minute poses. The right ones started out as two minute poses but when the model took his 15 and then 20 minute poses his head happened to be in the same positions, relative to me, allowing me to further develop them.
A twenty minute pose.
Another twenty minute pose, this time I roughly added the pure colors I saw within his skin tones with no thought to blending them into a more uniform flesh tone.