There was little if anything done to Patmore's face here. The background and suit were expanded. This is a lot of dark on dark, so I carefully studied Sargent's painting to see what was darker than what. I kept it all fairly subtle, as I did not want to detract from his head.
Adding these layers of dark with charcoal can be a real pain. You have to be patient and handle it slowly. Vary your stroke direction slightly with each pass. You want it to be even, but not blended. I don't really respond as well to cross hatching so much as oblique hatching - I find it to be richer and less predictable. There is no real way to verbally describe how to make a large, even tone of darkness with charcoal, but it is truly one of the hardest things to accomplish. If you've tried it, then you already know. I avoided any sharpness where the hair meets the background, as it will help it to disappear into the background. This is another effect that may be hard to see in life unless you are squinting. The cheek on the left was given a bit of a harder edge to help it pop, but not so much that it flattens the head. As I mentioned earlier, contours are a cheap solution and will only serve to ruin your hard work.