There are a lot of darks around the sitter's head in this painting, and I was getting to the point where I was going to have to address them before going any further with Patmore's face. I darkened the suit, background and the areas where his hair is lost in shadow.
If you look closely, you can see the first additions of white chalk on his face. Though they are not as bright as they will be at the end, these areas are what will ultimately be the lightest points on his face. I add them in slowly, as the paper is delicate and the chalk can be hard to remove without damaging the paper. I'd say that you can erase the chalk areas about three times total before the tooth of the paper begins to wear away, so it's best to add them in tentatively until you are positive that they are where you want them to be.
Even added in faintly, you can immediately see what I meant earlier about the toned paper acting as the transition areas. The forms are beginning to turn. I am keeping in mind that his collar and certain parts of his hair will be lighter than his face. Given that this is a master copy, Sargent has created the value scale for us already. Were this a live sitter, we would have to make some decisions as to how we wanted to play this. As long as it follows the rules of inevitability, then we could theoretically adjust the scale of light and dark however we wanted. Carrière might have kept the shadows very transparent and ghostly, whereas Ribera would have pushed the darks far deeper than they probably would have been in life. Sargent falls somewhere in the middle. In the end it doesn't matter - each painter has adjusted their tonal scale accordingly. They all made decisions to best highlight whatever the story is that they wanted to tell with their painting.