Some of your old books may contain hidden artworks: Beginning in the 17th century, a book’s binder would sometimes paint a watercolor scene on the edge of the book’s page stack. If the pages were then gilded, the image might remain hidden for years until the pages were fanned.

Sometimes two different images are hidden in the same book, revealed successively when the pages are fanned “up” and “down.” In rare cases paintings are hidden not just on the book’s fore edge but on the top and bottom as well, offering a panoramic view of the painting’s subject.