On-site Raman analysis of 17th and 18th century Limoges enamels: Implications on the European cobalt sources and the technological relationship between Limoges and Chinese enamels

Abstract

International audienceLimoges enamels on metal from the 17th to 18th centuries were analysed by non-invasive Raman microspectrometry with a mobile set-up in storage at the Musée des Arts Décoratifs (Paris) in order to identify the types of glazes and pigments used and to compare them with those found in Chinese cloisonné and falangcai enamels painted on metal and porcelain from the Kangxi and Yongzheng reigns (Qing dynasty). Certain French Jesuit and Chinese historical records report exchanges of technical know-how and artefacts during this period from France to China. Particular attention is paid to the detection of lead arsenate in blue and white enamels as well as in the whitened ones. Lead arsenate appears to be formed in blue enamels due to the high arsenic content of European cobalt ores exploited during the period in question

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

“…A similar feature was observed for the red garniture and carnation cheek of the lady (MNC 11234‐7, Figure b, right) and virgin (MNC 11234‐4, Figure c, right) figurines. This peak is characteristic of the As─O symmetric stretching mode arising from the arsenic ions used as a reducing agent for the precipitation of colloidal gold in the HNO 3 ─HCl mother mixture and then its dispersion of the resulting gold powder in the glassy matrix to obtain the ruby colour. Precipitation of colloidal gold with arsenic salt appears to be a characteristic of Perrot's methods whereas the Kunckel's method using precipitation with tin salts was more common in the 18th century production of ruby glass and Cassius purple glaze The narrow ~820 cm −1 peak is an indicator of the lead arsenate apatite phase Na 1 − x − 2y K x Ca y Pb 4 (AsO 4 ) 3 that is also formed by cooling on the reaction of cobalt ores containing arsenic (CoAs 2 , CoAs 3 , CoAsS, etc.…”

On‐site Raman study of artwork: Procedure and illustrative examples

“…Analysis of (a) an enamelled goblet (18th century Limoges Laudin family workshop) and (b) of a wucai Chinese porcelain vase using a high magnification (×200) long working distance (13 mm) microscope objective (see Colomban et al and Kirmizi et al for details); note the paper sheets used to protect from vibrations and to adjust the position of the spot in complement with the xyz stage; (b) the black textile covers the remote head and the artefact during the measurement…”

“…But the high toxicity of arsenic has limited the development of the technology. Recent on‐site studies of European soft‐paste porcelains and faience and of Limoges enamels demonstrated that lead arsenate was present in blue enamels. This arises from the use of cobalt arsenide to colour the glass, cobalt arsenides being the common mineral ores of the Erzgebirge mines in Saxony .…”

“…See Colomban et al [43] and Tournié [44] for details. Note the heavy piece of steel to stabilise the xyz stage (c; yellow arrow) FIGURE 2 Analysis of (a) an enamelled goblet (18th century Limoges Laudin family workshop) and (b) of a wucai Chinese porcelain vase using a high magnification (×200) long working distance (13 mm) microscope objective (see Colomban et al [49] and Kirmizi et al [50] for details); note the paper sheets used to protect from vibrations and to adjust the position of the spot in complement with the xyz stage; (b) the black textile covers the remote head and the artefact during the measurement ×200 Mitutoyo objective (spot waist <0.5 μ, i.e., close to the diffraction limit [48] ) renders possible the identification of a drawing's pigment regardless of the paper's huge fluorescence under green excitation. [51] Complex multicoloured décors for potteries are made by using a succession of thin glaze layers (the thickness being close to 10-20 μm, i.e., larger than the z-size of the focused spot obtained with ×50 or even ×100 microscope objective) and taking into account the broadening of the spot within the silicate glass.…”

“…Gemstones [30,33,37,40,41,126,127] Pigments of illuminated manuscripts [48,128,129] Wall paintings and frescoes [130,[132][133][134][135][136]144] Rock art [137][138][139][140][141] Buildings and stones [117][118][119]142,143] Glass, glaze, and pottery [31,32,43,[49][50][51][52][53][54]91,92,101,[103][104][105][106] Bronze corrosion and patina [123] Iron/steel corrosion layer and patina [114,116,117] Paintings pigments [13,125,…”