Not to be a downer on that, but I had some junk 
cels that I tried to "wash" and came up with 
three problems. First that the thicker areas of 
paint don't come off well with just alcohol - 
you'll use a *LOT* more alcohol that will make it 
worth it to have the acetate sheet. Second that 
the repeated alcohol washings you'll need to 
strip the thicker areas of paint will start to 
warp the acetate sheet so it is no longer flat. 
Third that quite a few of the paints stain the 
acetate from being left there for long periods - 
particularly the darker paints - and no amount of 
alcohol will remove the stains.

Trust me. . . Just go buy acetate and don't waste 
your time trying to reuse "junk cels". If you 
really want some acetate that badly, I could sell 
you a few sheets of what I have left over from a 
package I bought at the beginning of this year.

Many Sharp Smiles,
--Drac