A few facts you may not know about traditional hand painted cel Animation.
-The invention of the technique is generally attributed to Earl Hurd, who patented the process in 1914. The outline of the images are drawn on the front of the cel while colors are painted on the back to eliminate brushstrokes.
-Many studios including Disney simply wiped cels clean and reused them to save the cost of new sheets. Therefor examples from early animated movies and cartoons are hard to find.
-"The Band Concert" released by Disney in 1935, was the first color Mickey Mouse cartoon. An original cel from the cartoon was sold in a private transaction in 1999