On‐Site Raman and XRF Study of Complex Metal Patinas and <i>Cloisonné</i> Enamels From 19th‐Century Christofle Masterpieces: Technological Study of the Decoration Techniques

ABSTRACT A major effort in technological development was conducted during the 19th century. The polychrome surfaces of the metal parts of a corner cabinet, a torch vase, an “elephant” vase, and a candelabra pair designed by Emile Reiber between 1874 and 1878 for the Christofle &amp; Cie Company were investigated on site by means of noninvasive Raman, FTIR, and X‐ray fluorescence spectroscopy after examination under white light at different magnifications and under UV illumination. Despite the low thickness of the patinas (a few tens of microns) different (electro)chemically formed phases were identified in these layers (Cu 2 O, Ag 2 S, CuS or Cu 2 S, and sulfates). Residues of organic conservation products are identified by FTIR reflectance. The results are compared with the information available in the patents filed by the company as well as other written sources from that period. The pigments and opacifiers (Naples yellows, lead arsenates, fluorite, spinels, cassiterite, and chromates), and the vitreous matrices of the cloisonné enamels of the objects above are identified and testify to the deliberate combination of European and Asian enameling techniques.