A first draft of the script for Steamboat Willie, the first successful Mickey Mouse cartoon, is offered in an auction at animation conservation studio S/R Labs.
The lot dates to May 2, 1928 and is one of animation's founding documents.
It was written by Walt Disney and Ub Iwerks.
While Mickey and Minnie Mouse had earlier appeared in Plane Crazy, Steamboat Willie was the first Disney reel to be distributed to theatres.
It was an enormous hit, in part due to its innovative use of synchronised sound.
Ron Stark, director of S/R Laboratories Animation Art Conservation Center, explained that it: "not only saved the Disney Studio after the loss of Oswald the Lucky Rabbit, but singlehandedly gave animation itself, which had been showing serious signs of having outlived its novelty, a shot in the arm so powerful it saved the entire industry and propelled both it and Walt's new star into one of the great forces of modern times."
The script has been examined by Ub's son David, who is a leading authority on his father's work.
Stark said: "David Iwerks spent a considerable amount of time examining all the pages of the draft from every aspect, applying his first-hand knowledge of his father's artistic style and thinking, as well as what he knows of the history of that time.
"His conclusion was definitive: the draft and its drawings are unquestionably authentic."
The script is offered with an opening bid of $300,000 ahead of the October 24 sale date.
We have this copy of Walt Disney's America signed by some of the studio's principal animators and voice actors.
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