Three special kinds of art books that can really help:
Catalogues Raisonnés
"All the works of an artist". A scholar or a group of scholars documents every work of an artist's career. Each work is pictured, with scholarly opinions, provenance (where the work has been), literature about the work, and spurious works (forgeries). The first place to start when researching an artist or individual work. Not all artists have catalogues raisonnés. Very few for the ancient world.
Corpora
Like a catalogue raisonné, only for a single kind of object. Famous corpora are written for Greek pottery (Corpus Vasorum Antiquorum), stain glass windows (Corpus Vitrirarum) and Florentine altarpieces (Offner).
Duke Libraries' holdings of Etruscan Corpora -Duke catalog search
Permanent Holdings Catalogs (of museums)
Detailed catalogs of a period or genre of art in a particular museum. Like a catalogue raisonné, it will contain a collection of scholar's opinion on an object, conservation reports, provenance and literature (written about it). If you know of the location of a work of art, check for permanent holdings catalogs.
Etruscan art in the Metropolitan Museum of Art - Etruscan art owned by the Metropolitan, with essays.
