Characterization of the imperial architectural ornament papers in the Yanqu Building, the Forbidden City

Architectural pasting ornament, as a quintessential traditional Chinese interior finishing technique utilizing paper and textile materials, was particularly prominent in imperial constructions during the Ming-Qing transitional period. The exquisitely preserved ornament papers were found in the Yanqu Building (1772 CE) within the Qianlong Garden complex of the Forbidden City. A multidisciplinary analytical approach incorporating ultra-depth 3D video microscopy, polarized light microscopy (PLM), scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM-EDS), Raman spectroscopy, and thermally assisted hydrolysis-methylation pyrolysis gas chromatography/mass spectrometry (THM-Py-GC/MS) was systematically employed to investigate materials of the architectural ornament papers including the printed papers, pigments, and adhesives. The findings reveal that the multi-layer papers comprised mulberry bark papers and bamboo papers; pigment analysis identified copper resinate in passionflower floral scroll and coiled dragon motifs, lead white in swastika motifs, and muscovite as ground layer; adhesives characterization demonstrated the use of animal glue and pine resin in paint, with starch for paper laminations. The ornament papers had been renovated at least twice. Significantly, the first scientific identification of copper resinate - a translucent green glaze pigment - in the architectural decorations of the Forbidden City, provides new material evidence for understanding the technical evolution of Qing imperial decorative practices.