A non-invasive on-site Raman and pXRF study of the pigments and glassy matrix of 17th-18th century enamelled French watches

International audiencePainted enamelling technique on watches as a new form of fine art emerged circa 1630 in France. This study reports the on-site characterization of twelve enamelled watches dating to the 17th and 18th centuries from the collections of Musée du Louvre in Paris. Due to the rareness and high quality of the artefacts, analyses were carried out with a non-invasive approach by mobile Raman microspectroscopy and partially by pXRF. The enamels were found to contain pigments such as Naples Yellow pyrochlore, hematite, carbon, lapis lazuli, arsenic sulphide, manganese oxides and opacifiers such as cassiterite and lead arsenate. Lead-rich silicate compositions were identified for the corresponding glassy matrix of the enamels. An interesting outcome is that different hues of the enamels had been obtained by mixing many colouring agents, rather than using pure pigments as in the case of Limoges enamelled objects. The characteristic Raman signature of lead arsenate apatite detected in some of the 17th century blue enamels is related to the use of arsenic-rich European cobalt ores, as also characterized in the blue areas of French (soft-paste) porcelain decors and high quality Limoges enamels for the same period [1-3]. The presence of colloidal gold (Au° nanoparticles) was also indirectly detected by Raman analysis in the red-related areas of the 18th century watches. At least, three types of Naples Yellow pigment were identified with Sb-rich, Sn-rich and mixed compositions [4]. [1] Ph. Colomban, L. Arberet, B. Kırmızı, On-site Raman analysis of 17th and18th century Limoges enamels: Implications on the European cobalt sources and the technological relationship between Limoges and Chinese enamels, Ceram. Int. 43 [13] (2017) 10158-10165.[2] Ph. Colomban, T.-A. Lu, V. Milande, Non-invasive on-site Raman study of blue-decorated early soft-paste porcelain: the use of arsenic-rich (European) cobalt ores – Comparison with huafalang Chinese porcelains, Ceram. Int. 44 [8] (2018) 9018-9026. [3] Ph. Colomban, M. Maggetti, A. d’Albis, Non-invasive Raman identification of crystalline and glassy phases in a 1781 Sèvres Royal Factory soft paste porcelain plate, J. Eur. Ceram. Soc. 38 [15] (2018) 5228-5233. [4] Ph. Colomban, B. Kırmızı, C. Gougeon, M. Gironda, C. Cardinal, Pigments and glassy matrix of the 17th-18th century enamelled French watches: A non-invasive on-site Raman and pXRF study, J. Cult. Herit. (2020) in press