When is Art Deco not Art Deco?

The Modernist Brotherton Wing of Leeds
Infirmary. The curved balcony was
 functional, to allow patients to take in
sun and air

Some claim Art Deco originates in the 1925 French art expo at Le Musee des Arts Decoratifs. The exposition was intended as a display of new design from around the world, although the Americans didn’t participate. However Art Deco style works can be seen in Europe 10 and even 15 years prior to the expo.

The answer to the title question is probably when it’s Modernism, which is quite often. According to the V & A (who should know) the actual term ‘Art Deco’ wasn’t invented until the 1960’s, so to describe buildings from 50 years earlier as Art Deco does seems curious, but that's what art historians do. 

Perhaps the clue to identifying Art Deco lies in the word Deco. It implies decoration rather than function, which was the guiding thought in Modernism. From restrained lines to sunbursts and elaborate Egyptian styling, Deco is frequently applied to the surface of a building rather than incorporated into the basic structure.

Art Deco wasn’t labeled a separate category from Modernism until a 1966 retrospective on the 1925 exposition, when Patricia Bayer described Art Deco as "an architecture of ornament, geometry, energy, retrospection, optimism, color, texture, light and at times even symbolism."(from ‘Art Deco Architecture: Design, Decoration and Detail from the Twenties and Thirties,’ by Patricia Bayer, published 1992)

Art Deco chippy, Roundhay, Leeds. The design is
aesthetically  very pleasing, but not necessary for the
take-away to function.

Today, Art Deco refers to a style that moved from the boom of the roaring twenties to the bust of the Depression-ridden thirties. Art Deco represented many things to many people. In the twenties and thirties it was the style of the Jazz age, trans-Atlantic liners and New York skyscrapers, the fantasy world of cinema and also the real world of the factory, the tube station and the housing estate. Art Deco was popular and aspirational, it affected all forms of design, from fine art to fashion, film and photography to transport, product design and of course architecture. Art Deco was modern and it was everywhere, it just wasn’t called Art Deco.

Art Deco took the machine age and designed according to that imagery, using modern materials and retrospective flourishes. Modernism took the machine age and used it as reason to dismiss all that had gone before in architecture, it embraced pure form and practical purpose in design; ergonomic design is modernist, aesthetic design of the same period may be Art Deco.

Despite its recent increase in popularity, Deco isn't everybody’s favourite design style, but then neither is Modernism or Georgian for that matter. In the 21^st century maybe it's best to forget the stylistic preferences of the past, take and reuse anything which is useful today and then just move on.