Yes , You are right , I had been asked your question to myself when I bought Arthur Nash Notebook on Tiffany Glass Recipes. He kept formulas from even Tiffany. Tiffany did many attemps to learn the recipes but recipe book are opened to public only 10 years ago . Nobody knows how Tiffany created his glass colors and tricks, how the others recipes are older or not. And main red coloring material today is copper for red. Gold left out from the industry long time ago. Lycurgus Cup is different , it does not use gold as dye but uses gold nanoparticles as the two color for two lighting condition. Its totally different technology.