Cels Forum

My animator friend recommends taking a hair drier on low warm 
setting and running it on the back of the pencil sketch to warm the 
paper.
Never rip or tear anything.
Gently warm the paper gradually and gently pull, making very sure that 
no paint is coming on the paper as you. If it seems to be coming off, 
set it aside for a few minutes and come back to try again.
This is if you absolutely must try it.
Good luck.