Distinguishing Genuine Imperial Qing Dynasty Porcelain from Ancient Replicas by On-Site Non-Invasive XRF and Raman Spectroscopy

Abstract

The combined use of non-invasive on-site portable techniques, Raman microscopy, and X-ray fluorescence spectroscopy on seven imperial bowls and two decorated dishes, attributed to the reigns of the Kangxi, Yongzheng, Qianlong, and Daoguang emperors (Qing Dynasty), allows the identification of the coloring agents/opacifiers and composition types of the glazes and painted enamels. Particular attention is paid to the analysis of the elements used in the (blue) marks and those found in the blue, yellow, red, and honey/gilded backgrounds on which, or in reserve, a floral motif is principally drawn. The honey-colored background is made with gold nanoparticles associated with a lead- and arsenic-based flux. One of the red backgrounds is also based on gold nanoparticles, the second containing copper nanoparticles, both in lead-based silicate enamels like the blue and yellow backgrounds. Tin and arsenic are observed, but cassiterite (SnO2) is clearly observed in one of the painted decors (dish) and in A676 yellow, whereas lead (calcium/potassium) arsenate is identified in most of the enamels. Yellow color is achieved with Pb-Sn-Sb pyrochlore (Naples yellow) with various Sb contents, although green color is mainly based on lead-tin oxide mixed with blue enamel. The technical solutions appear very different from one object to another, which leads one to think that each bowl is really a unique object and not an item produced in small series. The visual examination of some marks shows that they were made in overglaze (A608, A616, A630, A672). It is obvious that different types of cobalt sources were used for the imprinting of the marks: cobalt rich in manganese for bowl A615 (Yongzheng reign), cobalt rich in arsenic for bowl A613 (but not the blue mark), cobalt with copper (A616), and cobalt rich in arsenic and copper (A672). Thus, we have a variety of cobalt sources/mixtures. The high purity of cobalt used for A677 bowl indicates a production after ~1830–1850.

Non-Invasive On-Site pXRF Analysis of Coloring Agents, Marks and Enamels of Qing Imperial and Non-Imperial Porcelain

“…The procedure has been described in previous articles in detail [12][13][14][15][16]30]. X-ray fluorescence analysis was performed on site using a portable ELIO instrument.…”

“…The data fitting procedure has been already used in previous papers [15,16]. After recording the raw data with ELIO, the spectra files were opened in the Artax 7.4.0.0 (Bruker, AXS GmbH, Karlsruhe, Germany) software.…”

“…The analysis must often be done in the secure place of storage or exhibition. Our previous works [10][11][12][13][14][15][16]30,48] have shown that the combination of mobile X-ray fluorescence (pXRF) instruments (information on the chemical elements present) and a mobile Raman microspectroscopy set-up (information on the 'molecular' structure, i.e., on the crystalline phases or amorphous) identified the coloring agents and phases present in the glazes and enamels, thus making it possible to compare the raw materials and techniques that were used for preparing, laying and firing the decorations, despite the impossibility of observing the stratigraphy as it is possible on a fracture or a shard [24,25,29,[31][32][33][34]. However, for a perfect interpretation of the results, the study by the same instruments and other more powerful ones (in particular SEM-EDS, XRD, PIXE and PIGE) in the laboratory of similar shards is essential.…”

“…We added to the corpus 19th century porcelains which may have been made after 1850, i.e., using as coloring agents chemically purified raw materials and not 'simple' minerals empirically selected and partially transformed by roasting and/or acid attack [6,59]. For comparison, some Canton metalware and Yixing red stoneware previously analyzed were also included [10,15,16]. Fourteen pieces from the Musée national des arts asiatiques-Guimet and eight from the Départment des objets d'art du Musée du Louvre were selected.…”

“…Painted enamel decorations, as opposed to ceramics decorated under glaze (typically blue-and-white porcelain) and by monochrome enamels or made by nearly homogeneous colored areas are particularly complex because, to represent sophisticated compositions as in oil painting, the glazes must be heterogeneous at different scales (overlay of layers, distribution of pigments and coloring agents). We will then compare the results with those obtained on similar pieces from the Chinese museum of the Château de Fontainebleau [13,14] and the Swiss museums of the Baur Foundation and the Ariana museum [15,16] as well as with sets of Chinese and Vietnamese ceramics from previous dynasties (Ming and Yuan) [17][18][19]. Such a set of exceptional Qing artifacts has never been analyzed or discussed hitherto.…”