The link above goes to a list of fictional works that feature art conservators &/or restorers. The idea of restoring or conserving a painting, that then becomes central to an unfolding mystery, is pretty popular with novelists these days. I'm partial to Iain Pears' art history mysteries, as well. Arturo Perez-Reverte's "The Flanders Panel" is probably one of my favorite books on the list. This list is well-annotated, and you can find a lot of these through your local library.
Jonathan Harr's "The Lost Painting," about the rediscovery of a Caravaggio masterpiece, is non-fiction but reads like a really excellent mystery novel.