One of the most extraordinary pieces made in Tiffany’s jewelry workshop at the turn of the 20th century is a pink tourmaline iris brooch signed by George Paulding Farnham (1859-1927). Audrey Friedman, co-founder with her husband, Haim Manishevitz, of the Primavera Gallery, bought it at Christie’s in the early 1990s for their private collection. This summer I was lucky…