One of the most beautiful and collectible Loetz series from this period is called Phänomen, whose chief characteristic is the rippled or featherlike designs on the object's surface. The company patented the Phänomen technique in 1898 and used it in combination with techniques pioneered by L.C. Tiffany in the United States—in particular, Tiffany's iridescent Favrile work. Combined, the two techniques provided plenty of inspiration for Loetz designers and artisans, including E. Prochaska, Franz Hofstötter, and Koloman Moser.
After 1905, when interest in the florals waned, Loetz pushed its surface treatments further than ever while relying on shapes that had been with the company for decades. Without a doubt, the most memorable Loetz art glass from the end of the Art Nouveau era is the Tango series. Unlike the work that had preceded it, which was all about dense color combinations and tricky surface treatments, these two-toned pieces typically featured single colors on mostly unadorned surfaces, with contrasting lip wraps or handles.