Art Nouveau is an international style of art, architecture, and applied art, especially the decorative arts, known in different languages by different names: Jugendstil in German, Stile Liberty in Italian, Modernisme català in Catalan, etc. In English it is also known as the Modern Style (British Art Nouveau style). The style was most popular between 1890 and 1910. It was a reaction against the academic art, eclecticism and historicism of 19th century architecture and decoration. It was often inspired by natural forms such as the sinuous curves of plants and flowers. Other characteristics of Art Nouveau were a sense of dynamism and movement, often given by asymmetry or whiplash lines, and the use of modern materials, particularly iron, glass, ceramics and later concrete, to create unusual forms and larger open spaces. Reference: Wikipedia
Below are some examples and price guides of Art Nouveau items including a Jean Dunand folding screen and a gold, pearl and diamond necklace.