As you can see in the detail above the pencil sketch still shows through in places. This is the result of a conscious decision to work in a semi-transparent mode throughout the painting. I used very little water in mixing my paints and relied on matte medium instead. I thinned the paint to the consistency of melting butter, working up from a base of raw sienna by adding basic shadows first and finishing with semi opaque tones for highlights.
Detailed work in the face required switching down to a quarter inch flat brush. This is the smallest size brush I allowed myself to use, and I refused to use any rounds for portrait. Why avoid rounds? I find that these pointed brushes lure me into rendering details too soon and tend to cause me to tighten up as I paint. The whole point is to stay loose from beginning to end, while finding ways to hint at details rather than render them out.