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

Abstract

Bernard Perrot produced sophisticated glass objects from~1666-1709 in Orléans, 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 Orléans and Sèvres 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 (×200) 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°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.

Non-Invasive On-Site Raman Study of Pigments and Glassy Matrix of 17th–18th Century Painted Enamelled Chinese Metal Wares: Comparison with French Enamelling Technology

“…This implies a spectral background peaking at about 500-700 cm −1 (actually 500-600 nm) characteristic of fluorescence in relation with the presence of metal (Cu • or Au • ) nanoparticles used to obtain colour between red and violet/purple [24,[72][73][74][75][76][77][78][79]. By comparison with previous studies on Perrot's ruby glass [29] and French enamelled watches [24], we can state that use of Au • colloidal nanoparticles was carried out, as for Famille rose porcelain [39,[42][43][44]. This signature is also accompanied by the band characteristic of the As-O stretching mode in many cases (see e.g., Figure 9D, R958).…”

“…The strong and rather broad 825 cm −1 peak observed in the blue enamel of one artefact (the F1501 bottle) corresponds to the As-O stretching mode which suggests the precipitation of lead arsenate apatite in lead-based enamel matrix ( Figure 6C). This phase with the general formula Na 1-x-y/2 K x Ca y Pb 4 (AsO 4 ) 3 may display a range of solid solution compositions with Ca, K and Na arising from the fluxes used in the enamels [13,[28][29][30]42,43]. Lead arsenate apatite is a typical phase found in 17th-century European glassy artefacts such as blue-and-white soft-paste porcelains and Limoges enamels, due to the use of European cobalt ores rich in arsenic [13,27,28,44].…”

“…Their use was also confirmed in Byzantine glazed pottery [52], then continued with the onset of the Renaissance to later periods as a major pigment of ceramic glazes (majolica) and glasses as well as paintings [53][54][55][56][57][58][59][60][61][62]. Consequently, due to the strong characteristic Raman signature easily obtained (due to the very high polarizability of the Pb-O bond) and wide range of compositions accepted by the pyrochlore structure which can be used as the specific signature of a workshop, many analytical studies have dealt with this pigment class up to now [12,13,24,[26][27][28][29][30][36][37][38][50][51][52][53][54][55][56][57][58][59][60][61][62].…”

“…This signature is also accompanied by the band characteristic of the As-O stretching mode in many cases (see e.g., Figure 9D, R958). The presence of this band may indicate addition of arsenic to adjust the hue or the special technique of using arsenic salt for precipitation of colloidal gold to prepare the enamel precursor, which was first performed by the French glassmaker Bernard Perrot in the 17th century for the production of ruby glasses, some years before the Cassius purple preparation by Johann Kunckel [29,[72][73][74][75].…”

“…At that time, the decor of Chinese porcelains was only made with the blue underglaze decor or with 'couleurs transparentes' technique (wucai, use of transition metal ions dissolved in the silicate network of the glaze) [1,2,27,28] which led to decors rather similar to those obtained on paper with lavish or watercolour techniques. These productions did not permit representing a 'realistic' decor, as opposed to the well-delimited coloured areas filled with opaque enamels that were coloured with pigments and metal nanoparticles (called fencai or yangcai which mean foreign colours, or Famille rose regarding the porcelain for Western scholars), using techniques developed in Europe to decorate metal, glass and pottery which allowed for realizing miniature pictures of enamel [2,12,13,29,30], as in European easel oil paintings, tempera or pastels [31,32]. There is a series of Chinese terms to classify enamelled porcelains: doucai (meaning: bound colours), (su)sancai (three colours), wucai (five colours, also called Famille verte in Western literature), ruancai (soft colours), falangcai (enamels in the French style), fencai (powdered colours), yangcai (Western colours/Famille rose).…”