Here is an original piece of artwork made for the Hanna-Barbera GODZILLA series that mesmerized me as a five-year-old child. It's done in pencil, with a second blue pencil, apparently for corrections. If this was done to photocopy the art onto cels for painting (the Xerox process), then the blue pencil theoretically wouldn't show up, so I will leave that to those more experienced than I am.
It measures 10.5 x 12.5", standard cel size, and does have the "key" holes/slots at the bottom, so perhaps this artwork was used for pencil tests, but my theory would be that HB didn't spend a great deal of money on pencil tests at this point.
It doesn't show up in the picture, but there is a lovely tinge of light brown across the top of the page, denoting its age. Not only is this going straight into a frame, but a frame that includes acid-free backing for protection!