I used to make fairly elaborate Christmas cards, and for a few years I made "advent calendar"-type cards, incorporating the traditional twenty-four "doors" which are opened, one per day from December 1 to December 24, to reveal hidden surprises. For this one from 1983 (I probably drew it the same month the Turtles were created), I created this top layer depicting a fanciful Christmas-themed landscape.
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Then I drew this piece with the various images which would be revealed as each "door" was opened. This sheet would be glued (carefully, along the edges) underneath the top sheet.
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But that couldn't be done until after I had carefully pre-cut along three sides, with an X-Acto knife, each of the twenty-four "doors" so that they could be easily opened by the cards' recipients. I think this was the step that finally put me off doing these things -- it was a lot of work! -- PL
P.S. The finished card measured 8.5 by 11 inches. -- PL