I'm working really hard to get this finished up! I have yet to work on the lower section of red on the sofa, the legs, or the floor. After I get to that stuff, I think it will just be a little tweaking here and there across the composition.
This pic is cropped from the larger image, so some of the detail is lost.
I've been adding highlights by scumbling. I start by mixing up a very light color, in this case titanium white mixed with ultramarine blue, pthalo turquoise, and ivory black. Obviously, the mixture is almost completely white. I dab a small amount onto the canvas in the areas to be lightened. Then, I take a clean, old bristle brush that is in pretty bad shape and I would not otherwise use for painting, and I use it to scrub the paint thinly over the surface.
As paint builds up on the brush, I wipe it off on a rag and then begin scrubbing again. This helps create a nice glow as the underneath layers are visible through lighter top layer. In the above images, already scumbled areas include the forehead, brow bones, and upper cheek. The nose, chin, and lower cheek are waiting to be done.