Anatomical Characteristics and Ageing of a Challenging Cultural Heritage Support

Produced from the parenchymatous tissue of the stem pith of Tetrapanax papyrifer, the material known as pith paper served as a distinctive support medium for Chinese export paintings during the 19th and early 20th centuries. Today, it is commonly found in collections worldwide. Due to its inherently fragile structure, conservation interventions are often necessary. However, the material’s chemical composition and deterioration mechanisms remain poorly understood, which not only complicates treatment decisions but also undermines preventive conservation efforts. This study presents a systematic investigation into the anatomical structure and ageing behaviour of pith paper using a multi-analytical approach. Optical and scanning electron microscopy revealed a preserved honeycomb-like cellular architecture composed of thin-walled, entirely of non-lignified parenchyma cells, which contributes to the material’s mechanical fragility. Artificial ageing experiments showed a significant loss of flexibility, increased yellowing, and a decline in pH with ageing time. Infrared spectroscopy identified molecular changes consistent with cellulose chain scission, with decreases in O–H and C–O–C absorptions revealing acid-hydrolysis-driven breakdown, while colourimetry pointed to the formation of chromophoric degradation products. These findings offer a foundational understanding of pith paper’s vulnerabilities and provide essential insights for the development of informed conservation and storage strategies.