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Since 2004, scientific research on the damaged Giant Buddha statues and Buddhist paintings in Bamiyan, Afghanistan, has been conducted at various laboratories and large-scale facilities using mass-spectrometry techniques (GC-MS, LC-MS, LC-MS/MS, nano-LC/ESI-MS/MS), ELISA, and synchrotron-based micro-analyses) in parallel to conservation intervention. Studies on samples from these cultural heritage objects have shown that each is composed of a polychromatic multilayered structure with sizing layers, ground layers, painted layers, and glaze. The carefully produced complex multilayered structures were examined using optical microscopy (visible and UV light) as well as synchrotron-based infrared microscopy, both of which revealed various organic and inorganic components in each layer. High sensitivity bulk MS and ELISA methods were used to further identify details regarding organic materials, such as fatty acids and collagens, and these results suggest different vegetable oils and animal species of glues. For example, cow milk casein and cow skin glue were identified in the Eastern Giant Buddha, suggesting that casein was used as a sizing agent and the cow skin glue as a binder for painting. The wall paintings from Cave N(a) (mid-7th century AD) were found to have horse glue used as sizing and drying oil (poppyseed/walnuts/perilla oils) as a binding media. The paintings’ complex structures and their organic and inorganic materials were fully understood using both imaging and bulk methods, and thus, these methods help to reconstruct historical wall painting techniques in full.

Abstract Animal glues derived from collagen-rich tissue are widely used as adhesives and binders in artworks. Identification of the animal source of glue is important not only to understand the artistic technique and historical background, but also to conduct appropriate treatment for restoration and conservation of artworks. Recently, mass spectrometric approaches have been used for species identification of glue. However, it appears that the existing methods were not applied to samples containing multiple animal sources, and the range of target species has been limited because of incomplete sequence information of collagen in public databases. In the present study, we established a novel method for discrimination of glues from eight animals applicable to samples with multiple animal origins. Trypsin-digested glue samples were analyzed by LC–MS in multiple reaction monitoring mode, and the animal source was determined based on the detection patterns of 12 type I collagen-derived marker peptides. Using the database-independent method, we successfully identified the animal source of commercial products and found the declared species for some glues to be incorrect. In addition, some products were identified to contain two different animal origins. Relative abundance of the animal origins in several impure glues was estimated using the marker peptides, which helped to speculate the reason for the detection of multiple species. We analyzed a painting (The Harvest by Camille Pissarro, 1882) and clarified that glues used in the ground and size layers of the canvas were derived from cattle (~ 65%) and sheep (~ 35%).