Here's an overview of reference books that may be helpful in collecting Art Nouveau art.

Art Nouveau (DK Collector's Guides)

Author: Judith Miller
ISBN: 1405302518
Published:  May 2004
Publisher: Dorling Kindersley

Book description:

Whether a long-lived passion or a new found pleasure, explore the beauty and originality of Art Nouveau with this sumptuous collector's guide. From furniture to metalwork, jewellery to sculptures - over 1,100 individually priced items, with up-to-date valuations and unique historical information, are presented by subject area. With in-depth coverage of all the major designers and factories, including Emile Galle and Charles Rennie Mackintosh, you can't afford to buy or sell without it.

Viennese Silver
Modern design 1780-1918

Author: Markus Brüderlin et al.
ISBN: 3775713174
Published: September 2003
Publisher: Hatje Cantz Publishers

Book description:

The history of modern design is not only older but much more multifaceted than commonly assumed. This thesis is elegantly borne out through an exploration of the work and influence of the Vienna avant-garde of the Biedermeier period, an era that brought forth shapes and forms which have lost none of their appeal, even today. If the towering objects that appear together on the cover of this book give the effect of a futuristic city, they thereby prove that their design stands the test of time, resoundingly relevant to our current design view thanks to its creative innovation. In fin-de-siècle Vienna, the designs of Josef Hoffman and Koloman Moser for the Wiener Werkstätte were informed by the intellectual content of that time. Since then, many of their ideas and the ideas of the Vienna avant-garde found their way into mass production; in this way have they trickled down into today's design vocabulary, primarily via the Bauhaus and de Stijl movements. Viennese Silver: An Adventure in Time 1800-1900 compares 180 carefully selected Viennese silver objects from the classicist to the Wiener Werkstätte periods with 20th-century architectural and design objects, exploring the question of Vienna's contribution to the development of modern design.

    Archibald Knox 

Author: Stephen A. Martin
ISBN: 1902889029
Published: December 2008
Publisher: Trans-Atlantic Publications, Inc

Book description:

The definitive sourcebook on the life and work of Archibald Knox.

  Modern art of metalwork.

ISBN: 3980152596
Published: 2001
Publisher: Berlin Bröhan-Museum

Book description:

Issued by the "Bröhan-Museum", State Museum of Art Nouveau, Art Deco and Functionalism (1889-1939). Berlin.

This book is the bible for the Art Nouveau metalwork collector.