Both European and Asian historical records report that Jesuits were at the origin of enamelling technology transfers from France (and Italy) to Asia during the 17 th century. A mobile Raman setup equipped with a high magnification (x200) microscope objective with long working distance is used to identify the use of European (arsenic-rich) cobalt in 17 th and 18 th century porcelains: twenty soft-paste porcelains from Rouen (L. Poterat' Factory), Saint-Cloud, Paris (Pavie', Hébert', Chicanneau', and Bellevaux' factories), Lille, Mennecy, and Vincennes factories, of which almost all were produced before 1750, belonging to the Cité de la Céramique Collection (formerly Musée national de Céramique, Sèvres), have been analysed in order to get a more representative view of the type of cobalt ore used. A large proportion of blue decors exhibit signs of lead arsenate, even for productions after ~1750, which proves the wilful interest given to arsenic phases in magnifying blue hues. Different lead arsenate signatures are observed, one assigned to the product of reaction of As-rich cobalt ore with lead-based glaze and another characteristic of added arsenic. At least two groups of glaze are identified: a lead-rich one and a mixed lead-alkali glaze. Porcelains made during the second half of the 18 th century exhibit the very strong As-O modes characteristic of the voluntary addition of a lead-arsenate forming compound. Comparisons are made with Qing Chinese productions exhibiting similar Raman signatures and expected to have benefited from transfers of technologies.

Optical microscopy, X-ray diffraction, X-ray fluorescence and scanning electron microscopy analyses were carried out on a typical Sèvres soft (frit) porcelain plate from 1781 in order to determine the chemical and mineralogical composition as well as the microstructure of its ceramic body, glaze, overglaze decoration and gilding. The body is rich in SiO 2 (73 mass%), CaO (16) and alkali oxide (8) and shows acicular wollastonite and tridymite crystals embedded in a glassy matrix consisting of SiO 2 (75), K 2 O (12) and CaO (9). The 50-90 mm thick, transparent lead glaze (40.9 PbO) contains 47.6 SiO 2 , 6.5 K 2 O and 3.5 CaO and shows a 35-75 mm thick reaction zone (50 SiO 2 , 30 PbO, 14 CaO) towards the body. The maximum thickness of the different paints is 50 mm, with 15 mm as mean thickness of the individual paint stroke. Two blue colours, for the dentil comb and the flower painting, are chemically distinct (colouring CoO in the dental rim 7, in the flower's blue 2 mass%) and contain many As-and Pb-rich globules and dendrites. Pseudohexagonal shaped platelets of Pb-Sb-Sn triple oxide crystals, embedded in a colourless glassy matrix, generate the opacity and the colour of the yellow paints. Opaque olive green colours are created by the combination of such yellow crystals with a bluish, Cu and Co bearing glassy matrix. The opaque red overglaze enamel is a mechanical mix of yellow Pb-Sb oxide crystals with an iron-rich (16 Fe 2 O 3) Pb-silica glass. Purple is very homogeneous and shows tiny drops of pure gold (max. diam. 0.5 mm) in a glassy matrix (47 PbO, 46 SiO 2 , 5 K 2 O). Violet is a mechanical blend of flower's blue and purple. The pure (99.5 Au, 0.5 Fe 2 O 3) gilt consists of several folded gold particles. The results of this study are only broadly consistent with the archival documented 18 th century technologies. The compositional dissimilarities of the studied enamels suggest that each colour was independently fritted. Consequently, the original colour recipes written down by Hellot in 1753 must have been modified in the 30 years since then.