Those painted page edges with no sealant? Check your books after 3 weeks.
I stained a set of old sci-fi paperbacks from Half Price Books in Austin with acrylic paint, just the fore-edge, and skipped the sealant step because I was rushing. Three weeks later, the paint started flaking off onto my fingers every time I pulled one off the shelf. Why does everyone keep skipping the varnish or wax layer? Has anyone found a finish that actually holds up on matte paper without making the pages stick together?
I ran into the same flaking with a batch of old Asimov paperbacks I did last year, learned my lesson fast. What finally worked for me was a super thin coat of matte Mod Podge, like barely any on the brush, then I fanned the pages while it dried so nothing stuck. The trick is doing it in two or three baby coats instead of one thick one, and letting each coat dry for a full day before you close the book. Also, sanding the fore-edge lightly with 400 grit before you paint helps the paint grab onto something. Mine have been sitting on the shelf for like six months now and no flaking, no sticky pages.