During the late 1800s, a new art spread throughout Europe and major American cities. This movement, known as Art Nouveau, was an art movement and style of decoration and architecture of the late nineteenth and early twentieth centuries. Artists and designers who created Art Nouveau aimed to transform their world by challenging convention, based on sources such as plant forms, Celtic patterns, and Japanese art. Art Nouveau, characterized with its graceful, asymmetrical lines based on organic forms, and exotic, rich imagery, is among the most immediately recognizable and widely appreciated of all artistic styles. In another sense it includes the geometrical and more abstract patterns and rhythms that were part of the general art in the 19th century. The exponents of this style insisted that all types of art should be equal, accessible and to be enjoyed by everyone: "Art for art's sake". There are wide variations used in this style according to where it appeared and the materials that were used. Art Nouveau designers demonstrated an appreciation of the natural world and were inspired by the depiction of lines of flowers, animals, insects, birds and plants. They used different woods, molten glass, clay and metal, and applied them to the flowing curves we see in buildings, furniture, jewelry, ceramics, glass and sculpture. Art Nouveau had qualities for intended visual experiences that were to be important to the twentieth century. The graphic style of Art Nouveau portrayed a balance between space and line. Unlike other cluttered designs, Art Nouveau used open space and pattern to create forms. Art Nouveau artists aimed at unifying all arts, centering it around man and his life. Therefore architecture, which has a direct influence on mans life, was the central art. Louis Sullivan is regarded today as one of the most individual and innovative architects of the developing modern period.