John Hubley's Moonbird

insight and history via Michael Sporn:

"In 1959, Moonbird took a giant leap forward. The art style borrowed from the expressionists, but used a method of double exposures to layer the characters into the backgrounds. Each animation drawing was painted black outside the border of its lines. Moonbird, the character, was colored with clear wax crayon and painted with black ink. The black resisted where the wax stood and gave a loose scribbled coloring. All of these painted drawings were photographed as double exposures, shot at less than 100%, to combine characters with Bgs.

The soundtrack involved an improvised track of two children, Mark and Ray Hubley, playing. These were recorded in sessions within a recording studio and massively edited down to create the final tracks."

I would love to see the non-YouTube version. The expressions of the kids are so human.