My latest project is a portrait of Aretha Franklin. I have found that working left to right in a portrait (I am right handed.) works better so that I do not erase with my right hand an area that I had previously worked on. (However, with my last portrait, Ruth Bader Ginsburg, it meant redoing sections of the portrait 3 or more times because it became apparent only after more of the portrait was done that the previous areas were "wrong".)
However, in this portrait, Ms. Franklin was wearing a "fall" which makes rendering her hair difficult for me to render. Normally, I do not have such a hard time with hair, but in this portrait, there is a LOT of it.
