Cels can become stuck even long after they're
dry. I've had cels for which I don't have bags 
start to get stuck to the paper in my cel book. 
An unstuck cel layer started to stick to it's 
partner too. (I put a stop to that!) Whenever 
possible, I bag backgrounds separate from the 
cels and put single layers of cel bag between 
unstuck cel layers, with the whole of the cel in 
a second bag.

It sounds like a pain, but this does answer how 
you can keep a cel correctly positioned on it's 
background without putting tape on or staples in 
the background - a dab of double sided tape 
between the separately bagged background and cel 
and voila! It stays in place. ^_^

But I have to say also. . . I'm well aware we 
shouldn't touch our cels. But I still do. I scan 
*all* my cels out of the bags, and when I'm 
spending an extended time looking at any one cel, 
I will almost always remove it from the bag to 
view it. A little caution to always carefully 
wash your hands first - or wear gloves - will 
reduce some of the risk in doing this. . . Myself,
I don't worry about it too much. ^_^

Many Sharp Smiles,
--Drac