"They Were 11" was released in 1986; there's a 
possibility that the cel could easily decompose. 
I'm not sure exactly when the switch to acetate 
occured, but older cels, being organic, compose a 
lot more easily; hence putting alcohol on it 
might not be the best idea.Try it on the tiniest 
edge and wait a day or so to see, would be my 
advice. You're probably safe, as 1986 is probably 
after the switch, but you can never be too 
careful.

Judging from the color...is that a cel of King?

-Misha