By Elisabeth Horth — Art Nouveau was a huge movement. It wasn’t only about architecture; it touched every artistic discipline. It dealt with architecture, of course, but also with furniture, pottery, painting, and embroidery. In an Art Nouveau home, the artists took care of everything—the jewelry, the dress of the patron, the furniture, the garden, the lights and lamps, the stained-glass windows, the staircase, even the wallpaper. Before Art Nouveau, the decorative arts were divided into separate...