Mike As far as the resins and oils, " being in small quantities" I think it depends on the wood you are talking about as to the quantities. When you heat treat a bow properly you do it slow so it soaks deep into the wood is how I understand it so I would think the cells within are also being compressed, not just the surface. I will let Pat explain it him self as he knows allot more about the subject than I do. Maybe Marc st louis will chime in and give his spin on things too? He wrote a chapter in Tbb on heat treating.
Josh