In a case like this where you have to be extremely
accurate about perspective, I am working from my
photograph and the sketch I did. Because the canvas
is small (10" x 20") I am using a Papermate
sharpwriter that will maintain thin lines. Charcoal
is what I use when I do underdrawings for paintings
on canvas, but in this case it would not work well.
There you have it for the moment. Oh yes, and that
is a piece of kneaded eraser - great for shaping to
take out tiny errors!