Every artist has his or her own process. Mine involves a putting on and a taking off of pigment. Sometimes, I "destroy" (i.e. smear, join, neutralize, lessen the importance of) huge passages. I don't believe that any of the strokes is too precious to be replaced. Actually, that is quite a complex notion that literally keeps me spinning. Sometimes the take-aways are more pleasing than the add-ons. My eraser as well as blending stumps are so very helpful in charcoal drawings, as they become my weapons of destruction. (all done in a very peaceful way). "Der Lehrer" is an example of this process. John works at The College of Wooster. It is a very good thing that I did not become an accountant......