Check out this neat video that shows fore-edge painting on a book. It looks like magic, as the painting appears and disappears, according to how the book is held. I love it!
Fore-edge painting is “where the page block is fanned and an image applied to the stepped surface. If the page edges are themselves gilded or marbled, this results in the image disappearing when the book is relaxed. When refanned, the painting magically re-appears.”
There’s a ton more to explore on the site.
Thank you to Shelf Awareness for the link.