Non-invasive on-site Raman study of polychrome and white enamelled glass artefacts in imitation of porcelain assigned to Bernard Perrot and his followers

Bernard Perrot produced sophisticated glass objects from similar to 1666-1709 in Orleans, particularly white enamelled artefacts and ruby glass. We present here the first non-invasive Raman study of 16 polychrome and white enamelled glass artefacts that are assigned to Bernard Perrot or his followers. These glasses belong to the museum collections at Orleans and Sevres in France. The prominent characteristic of these artefacts is their white bodies that were produced in imitation of porcelain. The small thickness of enamel applied to these glasses imposes the use of a high magnification (x200) long working distance microscope objective for Raman analysis. Pigments and opacifiers were identified, and the production technology was discussed. White opacification was found to be obtained by three compounds: calcium phosphate (bone opacification) for blown utensils, calcium antimonate for figurines, and cassiterite for thin enamels. The use of characteristic arsenic-rich European cobalt was identified in the blue enamels with the characteristic Raman signature of lead arsenate apatite as observed for the 17th and 18th century French soft-paste porcelains and Limoges enamels. The easy Raman detection of arsenic-rich phases also allows on-site identification of ruby glasses produced according to Perrot's technique (formation of Au degrees colloids by reaction initiated with an arsenic salt). The amount and crystallinity of calcium phosphate being variable appears to be a potential tool to discriminate between different production periods or workshops.