Well, commercial paint thinners have other 
chemicals in them too. (Or are completely 
comprised of alternate chemicals today, I think.) 
But the point is, you're NOT supposed to be 
playing with the stuff near the paint. ^_~  It 
shoudn't damage the acetate - but when using 
mineral oil, mineral spirits, or alcohol, I would 
recommend always keeping a second clean wipe with 
you and wiping off the surface just cleaned.

Incientally, I've only used the rubbing alcohol 
and in that case, I put it on a Q-tip (the other 
dry end of the Q-tip is used to wipe the area 
I've just cleaned).

Another thing I've never seen anyone mention but 
which might help is lens paper. (The 100% non-
abrasive kind used to clean microscpe lenses.) 
This is only something I've just thought of now, 
though. . . General call: Has anyone tried using 
lens paper to clean a cel?

One more thought. . . I can't tell from your 
scan, but you might want to double-check that 
the "smudges" aren't *actually* little tiny 
abrasions in the surface of the cel. If the 
abrasions are tiny enough and grouped closely 
enough together, they can appear to be a smudge.

Many Sharp Smiles,
--Drac