Unveiling the art of René Lalique with XRF and Raman spectroscopy - Technological innovation in jewellery production

Twenty of the eighty-two jewels created by René Lalique, one of the most representative artists of the Art Nouveau movement, nowadays in the collection of the Calouste Gulbenkian Museum (Lisbon), were studied using mobile XRF, optical microscopy, and digital radiography to characterise the materials and identify the fabrication techniques. The jewellery is often a gold, sometimes patinated, support where more or less transparent coloured materials, such as enamels and precious stones, were included. Further information on the decoration techniques was searched using μXRF and μRaman spectroscopy by studying two of the most illustrative items of a polychrome effect search. Data show that metal casting was the main forming technique used by Lalique. The surface was frequently left in as-cast condition. Contrary to what literature refers, the yellow and green-yellow gold alloys employed contain 77 to 83 wt% Au, and the expected presence of Cd was not detected. When black-patinated, the gold surfaces were covered with an artificial layer that could be estimated to be in the order of 70-80 μm thick. This layer consists of a mixture of Ag and Cu sulphides. In some of the patinated areas, was also identified AgCl resulting from a corrosion process. As expected for 19th century enamels, the vitreous matrix is a silica-alkali glass containing Na2O and PbO. Lead-arsenic compounds have served as both opacifiers and white colouring materials. Data suggest that blue was obtained with copper and chromate minerals, and pink with iron oxides.