LOETZ. IRIDESCENT GLASS SOME OF IT RESEMBLING THAT OF TIFFANY. IT WAS PRODUCED BY THE BOHEMIAN FIRM OF J. LOETZ WITURE . MOST PIECES ARE NOT SIGNED. LOETZ was the premier Bohemian art glass manufacturer during the Art Nouveau period (or Jugendstil, as it was called in German-speaking countries) from roughly 1890 to 1920. Founded in 1840 by Johann Loetz in what is now the Czech Republic, the company became known for its innovative techniques, organic forms, and bold use of color.