Unraveling the ink composition of ancient palm leaf manuscript from Tibet: A multi-analytical study

As a unique writing support before the invention of paper, palm leaves have a longstanding history of use in documentation and cultural transmission. Palm-leaf manuscripts are esteemed as a precious cultural heritage of humanity. Notably, the ink of palm-leaf manuscripts is an indispensable medium for recording and spreading the content of precious manuscripts. The composition of the ink directly affects its long-term preservation stability and potential repair strategies. However, due to the difficulty in obtaining samples, there is still a lack of systematic research on the composition of inks of palm-leaf manuscripts, and related analyses remain extremely rare. To this end, ancient ink samples from 12th–13th-century palm-leaf manuscripts in Tibet were examined by multiple techniques, including optical microscope, Raman, transmission electron microscopy (TEM), pyrolysis gas chromatography and mass spectrometry analysis (Py-GC/MS), scanning electron microscopy (SEM), energy dispersive spectrometry (EDS), and infrared spectroscopy (FTIR), to explore the main composition and the combination method of ink. The analysis revealed that the ink used in the palm-leaf manuscript derived from oil combustion, providing direct evidence of lamp soot and adhered to the surface of the palm leaves using adhesives without penetrating into their interior as determined by Raman spectroscopy, SEM–EDS, and TEM. Py-GC/MS and FTIR analysis identified the presence of polycyclic aromatic hydrocarbons (PAHs), proteins, pectin, fats, and polysaccharides in the ink sample. These findings indicated that the ink likely contained adhesives such as animal glue (e.g., bone glue and leather glue), as well as plant gum. Additionally, lipids were detected in both the ink and the support samples. This study represents the first systematic confirmation of the ink type used in palm-leaf manuscripts and the corroboration of adhesive components through various scientific methods. These findings provide significant insights and direction for research into the processing techniques and conservation of ancient inks found in palm-leaf manuscripts.