Typical Japanese natural resin films, i.e., oriental lacquer films, cashew resin films, and drying oil polymers were characterized, and also an ancient coating was identified using two-stage pyrolysis-gas chromatography/ mass spectrometry (Py-GC/MS). Urushiol, laccol, and thitsiol components, which are the main constituents of the respective oriental lacquers, were detected by the pyrolysis at 400ῌ. Additionally, the pyrolysis products, which reflect the structure of the urushiol, laccol, and thitsiol polymers, were detected by pyrolysis at 500ῌ after pyrolysis at 400ῌ. All the results have shown a significant progress occurring in the side chain-side chain C῍C coupling and aromatic nucleus-side chain C῍O coupling of urushiol, laccol, and thitsiol concurrently with the formation of the respective lacquer films. The cashew resin film was found to be terminated with saturated cardols and cardanols by the pyrolysis at 400ῌ. Furthermore, pyrolysis at 500ῌ revealed that the autoxidative side chain-side chain C῍C coupling accelerated the cross-linking of trienyl-and dienylcardanols during the polymerization. The C4῍C18 free fatty acids were detected by the pyrolysis of the drying oil polymers. These pyrolysis products are significant markers for a drying oil polymer. The drying oil polymer is terminated with saturated fatty acids, especially with hexadecanoic acid and octadecanoic acid. Based on these results, the ancient coating sample obtained from the surface of a wooden dish excavated at Tobarikyu, Kyoto prefecture, Japan was identified as Rhus vernicifera lacquer combined with an drying oil, presumably added as the solvent. Py-GC/MS was proved to be e#ective for the characterization of natural resin films and identification of organic coatings of historic artifacts.
IntroductionFor a long time, main investigations in archaeology have been the researches of documentary records. Artifacts have been roughly dated by the stratum in which they have existed. They have been classified into porcelain, ceramics, earthenware, tile, metal, wood, and stone, and then weighed. After that, archaeologists have placed the exact date and their production district by the shape and figures on them. However, new technologies, i.e., microanalysis by a scanning electron microscopy (SEM), elemental analysis by electron probe micro analysisr (EPMA), and X-ray fluorescent analysis (XRF), and isotope analysis, are applied to archaeology in nowadays with the developments of scientific analysis. These new technologies make it possible to identify an unknown artifact and to determine its production age more accurately. They may change the history, which is taken for granted.In this study, the scientific analysis of organic coatings of historic artifacts is discussed. EPMA and XRF are e#ective to identify inorganic paints such as a wall painting, but not for organic coatings. Since the organic coatings consist of a few elements, it is di$cult to identify them using these methods. Furthermore, Fourier transform infrared spectroscopy (FT-IR) can...