Someone posted a video of an art professor giving a demonstration, where he did tonal charcoal drawing, covered it with shelak to seal and tone it, and after drying started to paint with oils over the top. I want to try the same thing, tonal drawing on canvas with charcoal and then use tinted clear gesso over the top to seal the drawing. Have any of you tried this? I have tried this with a brush and it just spread the charcoal all around ruining the drawing. I'm wondering if pour the gesso on and use a large putty knife to spread it, if that would work without distorting the drawing. Thoughts?