Full Spectral Range Raman Signatures Related to Changes in Enameling Technologies from the 18th to the 20th Century: Guidelines, Effectiveness and Limitations of the Raman Analysis

Abstract

This study investigates the comparison of the Raman signatures of different phases used in underglaze, inglaze and overglaze decors of selected European, Chinese and Japanese porcelains and enameled metalworks, which are particularly representative of technological developments in enameling. Specifically, the article deals with the main structural types or host networks (corundum/hematite, spinels, zircon, cassiterite, pyrochlore, apatite, sphene, etc.) used for colored enamels on porcelain, earthenware or metal rather than considering all types of pigments and opacifiers. According to the results, Raman microspectroscopy allows identifying of the fingerprint spectra of milestone technologies and represents a simple and rapid tool for detecting copies. Particular attention is paid to the information deduced from the examination of the associated ‘background’ and signatures from electronic transitions induced by uncontrolled traces or voluntary addition of rare earths (luminescence). The relationship between the grinding procedure and Raman signature is also discussed.

pXRF Data Evaluation Methodology for On-Site Analysis of Precious Artifacts: Cobalt Used in the Blue Decoration of Qing Dynasty Overglazed Porcelain Enameled at Customs District (Guangzhou), Jingdezhen and Zaobanchu (Beijing) Workshops

“…The A 615 bowl mark is rich in Mn, as observed for artifacts produced during the Ming Dynasty [23,26,27,29,[70][71][72][73][74][75][76][77][78][79][80][81][82][83][84][94][95][96][97][98][99][100][101]. A 'return' to traditional Chinese techniques has already been observed for Yongzheng productions [25].…”

“…Moreover, until the middle of the 20th century, there was only one other alternative, which allowed one to color in blue, namely a crystalline natural silicate, also known as lapis lazuli, a rare rock [23,36]. To date vanadium-doped zircon the main blue pigment is used [72]. The scarcity of cobalt has led to the recycling of blue glass since antiquity [23].…”

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

“…By identifying the phases, crystalline or amorphous, the Raman analysis makes it possible to go further in the identification of the enameling technique and coloring agents as well as the conditions of the decorations (see, e.g., references [44][45][46][50][51][52]55,57]). Remember that, due to the optics used, the volume analyzed is controlled at the micron scale, i.e., much smaller than the one probed by X-ray fluorescence.…”

“…The composition of the raw materials is, therefore, not constant, and the variability depends on the visual selection, natural solid solutions, and impurities of the minerals constituting the ores used and their 'purification' treatment. During the 19th century, mainly in the second half, the more or less 'purified' natural coloring products were replaced by 'chemicals', namely, salts (carbonates, sulfates, nitrates) or oxides with a much lower number of impurities [44][45][46][47][48][49][50][51][52]. Therefore, identifying the elements associated with those used to color enamels can be an effective authentication tool [50][51][52].…”

“…During the 19th century, mainly in the second half, the more or less 'purified' natural coloring products were replaced by 'chemicals', namely, salts (carbonates, sulfates, nitrates) or oxides with a much lower number of impurities [44][45][46][47][48][49][50][51][52]. Therefore, identifying the elements associated with those used to color enamels can be an effective authentication tool [50][51][52].…”