Art Nouveau bronze table lamp. Made by Verrerie de Vallerysthal (later Vallerysthal & Portieux). This is a historic glass and crystal factory founded in 1838 in Lorraine, France. This type of glass with iridescent colors – from light blue/white to deep blue – is called "verre multicouche" (multilayered glass) or sometimes achieved through the technique of "verre dégagé à l'acide" (acid etching), in which layers of colored glass are removed to reveal the underlying color and create an iridescent effect.