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In the 18th century, this kind of "fore-edge painting" was all the rage for high-end books, concealing an elaborate landscape scene that was invisible when the book was closed. Even though bored 20th century students were known to attempt a cheap version of this with their school notebooks, the labor and skill-intensive nature of this artform means there are very few practitioners of the art left today. This video is from the Cornell University Library's Rare Books department, and is a great demonstration of the kind of fine detail the world lost as mechanization took place (not that books books being affordable wasn't worth it):

Sources: Cornell University