The clear plastic animation cel, 1915: J. R. Bray was granted patents in 1915 for his use of a transparent substance (glassine paper) for his action drawings which were then placed over the background.
The most important part of this patent embraced a system of drawing
the background on a translucent sheet placed over character drawings,
thus eliminating the need to tediously redraw the background every
frame, as Winsor McCay had done. This was a radical departure from the
methods used up to that time. Bray also devised the "stationary"
drawing, which uses separate sheets of a transparent substance when
a moving part of the character is motionless while other parts are
in motion.
From about 1915 to 1932 Bray issued licenses to anyone who wanted to
make animated cartoons using the
CEL method he developed.
