Comparative analysis of eastern and western drying-oil binding media used in polychromic artworks by pyrolysis–gas chromatography/mass spectrometry under the influence of pigments

Material and Microstructure Analysis of Wood Color Paintings from Shaanxi Cangjie Temple, China

Cangjie Temple was built to commemorate Cangjie, the legendary inventor of Chinese characters. It stands as one of the few remaining temples in China dedicated to the invention and creation of writing. In this study, the material properties of wooden paintings from the Cangjie temple were characterized using Polarized Light Microscopy (PLM), Scanning Electron Microscopy coupled with Energy Dispersive X-ray Spectroscopy (SEM-EDS), Micro-confocal Raman Spectroscopy, X-ray Diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR), and Pyrolysis-Gas Chromatography-Mass Spectrometry (Py-GC/MS). It was confirmed that the pigments of the paintings included cinnabar, lapis lazuli, lead white, Paris green, and carbon black. The proteinaceous glue was used as an adhesive in the pigment samples, with tung oil likely being utilized as a primer for the wooden structures before painting. This study not only provides valuable data support for the conservation and restoration of the architectural features of Cangjie Temple but also provides useful reference for the maintenance and inheritance of similar ancient buildings.

A Study on the Materials Used in Ancient Wooden Architectural Paintings at DaZhong Gate in Confucius Temple, Qufu, Shandong, China

This study analyzes the pigments and binders used in the painted wooden structure of DaZhong Gate in the Confucius Temple in Qufu, Shandong Province, China. Five samples were collected from the building and analyzed using techniques such as polarized light microscopy (PLM), energy-dispersive X-ray spectroscopy (EDX), micro-Raman spectroscopy (m-RS), and Fourier-transform infrared spectroscopy (FT-IR). The findings reveal that the red, yellow, green, and blue pigments are identified as lead red, lead chromate yellow, emerald green, and ultramarine, respectively. The white pigment is determined to be a combination of chalk and lead white or anglesite. Considering the production period of the yellow and green pigments, it is inferred that architectural paintings underwent restoration or repainting during the late Qing Dynasty. The analysis of the binder in the pigment using pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS) reveals that the binder employed is a protein-based glue. Additionally, the detected presence of Heat-bodied tung oil suggests a potential connection to traditional Chinese painting techniques on wooden surfaces. This discovery not only contributes to the historical research of the Confucius Temple but also provides crucial data for the conservation and restoration efforts of this culturally significant heritage site.

A Study on the Materials Used in the Ancient Architectural Paintings from the Qing Dynasty Tibetan Buddhist Monastery of Puren, China

Situated in the village of Lama Temple on the eastern bank of the Wulie River in Chengde, Puren Temple stands as one of the few remaining royal temples of great importance from the Kangxi era (1662-1722 AD). This ancient edifice has greatly contributed to the advancement of our comprehension regarding the art of royal temple painting. The present study undertakes a comprehensive analysis and identification of nine samples obtained from the beams and ceiling paintings within the main hall of Puren Temple. Furthermore, a systematic examination of their mineral pigments and adhesives is conducted. The findings from polarized light microscopy (PLM), energy-type X-ray fluorescence spectrometer (ED-XRF), micro-Raman spectroscopy (m-RS), and X-ray diffractometer (XRD) analyses reveal that the pigments present in the main hall beams of Puren Temple are cinnabar, lead white, lapis lazuli, and lime green, while the pigments in the ceiling paintings consist of cinnabar, staghorn, lead white, lapis lazuli, and lime green. The use of animal glue as a binder for these pigments on both the main hall beams and ceiling paintings is confirmed via pyrolysis-gas chromatography-mass spectrometry (Py-Gc/Ms) results. These findings hold significant implications for the future restoration of Puren Temple, as they provide valuable guidance for the selection of appropriate restoration materials.

Characterization of Animal Protein-Based Binders in Ancient Chinese Wall Paintings Using Atomic Force Microscopy and Fourier Transform Infrared Spectroscopy

In this study, the topographical characteristics of protein-based binders in ancient Chinese wall paintings and the properties of their sources were investigated and identified. Fifteen samples of protein-based binders (skin glue, bone glue, egg glue, and milk glue) before and after aging and mixing azurite were prepared. Next, the topographical characteristics, adhesive properties, and infrared spectra for each chemical group in the binders were analyzed using atomic force microscopy and attenuated total reflection Fourier transform infrared spectroscopy (ATR FT-IR), and the sources of various binders were identified using ATR FT-IR and principal component analysis (PCA). Results showed that protein binders such as fish bladder, cow bone, and egg white glue had lower roughness values and good consolidation properties. The most distinctive feature of skin and bone glues before and after aging or mixed with azurite was the stretching vibration peak of CH₂ deformation vibration at around 1335 cm^-1, while the significant characteristics of egg and milk glue was the C=O stretching vibration in Serine at 1306 cm^-1 and C=O stretching vibrations in aspartic acid and glutamic acid at 1416 cm^-1. In addition, the significant differences of absorbance peaks were observed in the infrared spectra of various bone, skin, egg, and milk glue samples before and after aging while the spectral differences become insignificant after mixing with azurite. The results of PCA confirmed that egg yolk and ewe's and cow's milk were well differentiated from animal skin and bone glue regardless of whether fresh, aged, or mixed with azurite. In addition, the differences between skin and bone glues were significant, and the various types of bone glue could be also differentiated before and after aging.

Identification of polysaccharide binding materials used in cultural relics by pyrolysis-gas chromatography/mass spectrometry

热裂解-气相色谱/质谱(Py-GC/MS)技术能够实现微量样品中有机组分的准确、快速检测,非常适用于文物中各类天然有机材料的定性分析。该研究以中国古代书画、建筑、器物等文化遗产中常用的淀粉、桃胶,以及西方文化遗产中常用的阿拉伯胶等多糖类胶结材料为研究对象,系统分析并总结各类材料的Py-GC/MS特征裂解组分及辨别方法。研究发现,淀粉、桃胶、阿拉伯胶在色谱保留时间前段的裂解产物基本一致,主要是小分子呋喃、酮类组分;在保留时间中段3类材料的裂解产物主要是呋喃型酮等组分,但不同材料的具体裂解组分差异明显;在保留时间后段,3类材料检出多种单糖衍生物以及单糖低聚体衍生物,其中桃胶与阿拉伯胶裂解组分较为接近,但与淀粉完全不同。因此,可根据不同保留时间段淀粉、桃胶、阿拉伯胶裂解产物的差异实现3类材料的辨别,其中1,6-脱水-β-D-吡喃葡萄糖只在淀粉中检出且色谱峰强度高,可以作为识别淀粉的特征组分;此外,可根据桃胶、阿拉伯胶在保留时间后段的裂解产物主要质谱碎片离子m/z 60、m/z 101的提取离子流图分布特征实现其辨别。基于所建立的Py-GC/MS方法,研究推断故宫旧藏清代剔红云龙纹天球瓶瓶口部位黏结材料含有面粉,旻宁御笔并蒂含芳贴落画心纸所用黏结材料为面粉糨糊。该研究所建立方法及所总结的数据易于推广,适用于我国文物中多糖类材料的准确、快速识别,研究结果能为相关文物材质工艺的研究以及保护修复方案的制定提供科学依据。

Long-chain mercury carboxylates relevant to saponification in oil and tempera paintings: XRPD and ssNMR complementary study of their crystal structures

Saponification, resulting from pigment-binder interactions, is one of the most endangering phenomena affecting the appearance and stability of painted works of art. The crystallization of metal carboxylates (soaps) in paint layers is recently assumed as the most critical point for the development of undesirable changes induced by saponification, however, the factors triggering it are not fully understood. The red pigment cinnabar (HgS) has been suspected of contributing to saponification, however, the paucity of reliable reference structural data limited the experimental research of its effect at the molecular level. Within this study we synthesized mercury(II) carboxylates of the formula Hg(C16)_x(C18)_2-x (x = 0.0; 0.2; 0.5; 0.8; 1.0; 1.2; 1.5; 1.8; 2.0) where C16 and C18 are hexadecanoate (palmitate) and octadecanoate (stearate), respectively, and characterize them by combination of X-ray powder diffraction (XRPD) and ¹³C and ¹⁹⁹Hg solid state NMR (ssNMR). For a more detailed interpretation of their structural and thermal behavior, Fourier transform infrared spectroscopy (FTIR) and differential scanning calorimetry (DSC) were used. The crystal structure of the studied mercury carboxylates was described on the basis of complementary ssNMR and XRPD measurements, Rietveld refinement and DFT calculations. All the subjected compounds crystallize in a monoclinic lattice of the C2/c symmetry. Mercury atoms are arranged in a slightly distorted square antiprismatic geometry and are monodentatically bonded to carboxylate anions. The structural disorder at the aliphatic end of the stearic acid chains was detected in the mixed carboxylates. Within the paper, the structural (dis)similarity with the corresponding lead carboxylates is discussed. The synthesized and characterized mercury carboxylates were applied to describe neo-formed mercury soaps in a model experiment simulating an egg-based paint system.

Analytical Techniques for the Preservation of Cultural Heritage: Frontiers in Knowledge and Application

Chemistry is considered as the heart of preservation science. The archaeological objects are an organic-inorganic system and need comprehensive techniques to investigate the different materials with a high resolution and accuracy. The characterization process of archaeological materials is a useful guide to develop the right strategy for the conservation and intervention of the objects. In analytical chemistry practice, there are many techniques to employ the characterization process of the artworks: molecular, elemental, imaging, surface, thermal, separation, nuclear, dating, electrochemical, and miscellaneous techniques. It highlights the potential of chemical investigations to present reliable information to the conservators and art historians.

Investigation of Ancient Architectural Painting from the Taidong Tomb in the Western Qing Tombs, Hebei, China

The Taidong Tomb in the imperial tombs of the Qing dynasties has great aesthetic value and a rich history. In this study, we conducted the first investigation ever performed on the raw materials used in the paintings in the Taidong Tomb. Energy dispersive X-ray spectroscopy (EDX), polarized light microscopy (PLM), X-ray diffraction (XRD), micro-Raman spectroscopy (m-RS), Fourier-transform infrared spectroscopy (FTIR) and pyrolysis–gas chromatography–mass spectrometry (Py-GC/MS) were used to comprehensively analyze the painting of Long’en Hall, Xipei Hall and the ceiling of Minglou. In the conclusion of the study, the paintings were found to contain natural mineral and synthetic pigments, including atacamite (Cu2Cl(OH)3), azurite (2CuCO3·Cu(OH)2), vermilion (HgS), carbon black (C), anglesite (PbSO4), white lead (2PbCO3·Pb(OH)2), synthetic emerald green (Cu(CH3COO)2·3Cu(AsO2)2) and ultramarine ((Na,Ca)8(AlSiO4)6(SO4,S,Cl)2). This allows us to conclude that some of the architectural paintings were repainted in the mid-to-late 19th century. The mortar layer may consist of brick ash (albite, gismondine), lime water, tung oil and flour. The fiber layer material may be ramie. Researching the raw materials of the paintings in the Taidong Tomb is of great value because it provides scientific data for the future preservation of the paintings in the tomb.

Nontargeted Pattern Recognition in the Search for Pyrolysis Gas Chromatography/Mass Spectrometry Resin Markers in Historic Lacquered Objects

A differential expression analysis technology developed for linear modeling of gene expression data was used in combination with thermally assisted hydrolysis and methylation gas chromatography/mass spectrometry (THM-GC/MS) to support the analysis of lacquers and varnishes on historical objects. Exudates from tropical trees, such as Manila copal, sandarac, South American copal, and Congo copal, which were frequently used in finishing layers on decorative objects up to the early 20th century, were compared through this approach. Highly discriminating features indicate biomarkers that can help to identify copals in resinous lacquers. The approach allows new, more systematic ways for finding biomarkers in the analysis of lacquered objects of art and varnishes.