Secondary sources
Antique Boxes, Tea Caddies, & Society 1700-1880
Antigone Clarke & Joseph O’Kelly
Schiffer Publishing, 2003
A comprehensive, beautifully produced book well worth the money.
Mauchline ware, A Collector’s Guide
David Trachtenberg & Thomas Keith. Antique Collectors’ Club, 2002
Tunbridge Ware and Related European Decorative Woodwares Brian Austen
Foulsham, 2001
You may also find it useful to buy a book on silver hallmarks and makers' marks, although there are several comprehensive sites available on the internet See the Library section for details.
Here are details of some of the books that you might find useful in helping you understand more about visiting card cases and the decorative finishes in which they can be found.
Primary sources
Collecting Visiting Card Cases
Wladimir Herman, 2005
Visiting Cards and Cases
Edwin Banfield
Baros Books, 1989
Antique Pocket Guides: Visiting Card Cases
Noël Riley
Lutterworth Press, 1983
Antiques Price Guide 2003
Judith Miller
Dorling Kindersley, 2002
This colour edition of Millers has an extensive section on card cases. You should note though that the prices given, even in 2002, were on the low side in many instances.