Growing political tensions, the after-effects of the war, and a reaction against the perceived decadence of the turn of the century led to simpler forms, combined with more effective manufacturing for mass production of high-quality jewellery. Covering the period of the 1920s and 1930s, the style has become popularly known as Art Deco. Walter Gropius and the German Bauhaus movement, with their philosophy of "no barriers between artists and craftsmen" lead to some interesting and stylistically simplified forms. Modern materials were also introduced: plastics and aluminum were first used in jewellery, and of note are the chromed pendants of Russian born Bauhaus master Naum Slutzky. Technical mastery became as valued as the material itself; in the west, this period saw the reinvention of granulation by the German Elizabeth Treskow (although development of the re-invention has continued into the 1990s).