Scientific analysis of Japanese ornamental adhesives found in Shosoin treasures stored since the mid-eighth century

Shosoin treasures, stored in Japan continuously since the mid-eighth century, represent an important collection of beautifully decorated housing artworks made by gluing a variety of ornaments such as marquetry, metal, crystal, pearl, and amber. The ornamental adhesives used in the treasures were scientifically characterized by nondestructive methods such as attenuated total reflectance Fourier-transform infrared spectroscopy (ATR/FTIR) and X-ray analyses. FTIR spectroscopy was applied to the fragments of the following treasures: a red sandalwood armrest with marquetry decorations dedicated to Great Buddha of the Todaiji temple by Empress Komyo (701–760 AD), two biwa lutes with marquetry decoration, and the imperial ceremonial headdresses of Emperor Shomu (701–756 AD), Empress Komyo and Empress Koken (718–770 AD). Second-derivative transformation of the FTIR spectra identified the adhesives on the marquetry fragments as animal glue. The adhesives on the fragments of metal, crystal, pearl, and amber ornaments from the headdresses were identified as frankincense according to their IR absorbance and the second-derivative spectra. X-ray diffraction experiments and X-ray fluorescence spectrometry of the adhesives on the fragments of metal, crystal and pearl indicated that orpiment (As2S3) was mixed with the adhesives.