*Moved from another post to add info here on this post*

***OMG DON"T*** do what is said in these posts you will destroy your production drawings. The easiest and best way to remove stuck drawings is to lay your cel face down on a clean white T-shirt turned inside out(it's softer) next to a open window at night only. the moist air is enough to release the bonded weave of the paper from the paint. Each morning lightly tug up at the edges some will come loose each day. put a pencil between the paper and cel to hold open to the next nights air and after as little as a day or up to a week the drawing WILL come free and no harm will come to your drawings, take your time and don't rush if it takes longer than a week. This comes from a Disney archivist who showed me a great many years ago how to do it. Some use of a mister box has been used in the past but you have to have a super fine mist for this to work and it can cost alot to make one that will not soak your drawings. Use the night air, it works the best. if you have a covered screened porch all the better to lay them out under on a table. But never leave the artwork in the heat of the day or if it's going to rain, just put it out at night time with no chance of rain. I have done this to 2000 dollar cels very safely. good luck. Roy Aka Backlotanimation
Sorry other posters,I mean no insult only to educate from my past tests. If it's just tiny bits of paper from a bad removal of a drawing(sad indeed), it's best to just leave it and place a backing page to cover the back. I hate to see folks lose their production drawings as this is the real art not the cel. never just pull them off dry. remember the drawing was touched by the hand of the animator, the cel may not have been even looked at by the one who drew it. Even hand inked cels for the most part are done by inbetweeners not the animators they use the animators drawing to do the inking.
*added* never freeze your cels. think about it what happens to roads and side walks that freeze in winter? they crack. the paint can and will do this on your cels too, not always but enough not to do it. never run floss between them or you run the risk of pealing paint off the cel, better to have a unregistered or miss alined cel than damaging them.