Stage eleven is essentially just a continuation of stage ten. The other eye is further developed and darkened. I also started to break up the hair into locks. This has to be done carefully, otherwise you run the risk of the hair looking plastic. It is still hair, which means it must be handled differently than the rest of the face and clothing. It is a different texture and must be treated as such. The strokes of charcoal should be wispy and to a large extent need to follow the flow of hair. Be careful not to be too systematic about that though, as you don't want it to appear too mechanical. Most of his grey hair is going to fall in the midtone category, but there are certainly some glints of light that I began to establish. I like to think of the hair as a sculptor would - it needs to be broken up into the major forms, and then those forms need to be broken up into yet smaller forms. It all must hold together though, the smaller forms must be subservient to the larger ones. Hair still follows the same principles of light and dark as everything else though, so those rules still apply.
Now that I had some indication of the lights on his hair and collar, I went back into the face and started to elaborate on the chalk areas. The light is coming from above, so with the exception of a few tiny highlights (like the tip of the nose and lip) the light that is on the lower end of his head must be dimmer than the upper portion. His forehead will always be lighter than his chin, for example. This may not be easy to detect on a live sitter, and may need to be forced in order to get the effect you want. This is where you can use invention to meet your needs - as long as the principles and science of nature are respected, you can create illusions that will be more lively than life. In a drawing, you are able to push things that nature often diffuses. Welcome to the world of illusion!