Effects of Stone-Calendering on Traditional Handmade Paper: Mechanical Properties and Shape Stability

Abstract This study investigated the effects of stone-calendering on the mechanical properties and shape stability of three traditional handmade papers (xuan, bamboo, and hanji papers). Stone-calendering is widely adopted to enhance paper softness and smoothness, yet its material-specific impacts on mechanical performance and shape stability remain underexplored. We evaluated three sample groups – untreated, stone-calendered, and wax-treated stone-calendered papers – under controlled conditions, analyzing their basic properties (density, optical characteristics), mechanical performance (tensile strength, folding endurance), and shape stability. Digital Image Correlation (DIC) technology quantified shape stability under humidity cycling and accelerated dry heat ageing tests assessed ageing resistance. Results show that raw material composition is a critical factor determining paper responses to treatments: stone-calendering increased density and softness while reducing surface roughness across all samples, but pre-calendering wax treatment compromised tensile strength (attributed to weakened inter-fibre bonding). While all paper samples exhibited progressive discoloration during ageing, wax-treated stone-calendered samples showed slightly higher color difference values than untreated and stone-calendered samples, suggesting a potential minor effect of wax components that needs further investigation. Notably, hanji exhibited superior shape stability after stone-calendering, especially under humidity cycling, whereas xuan paper displayed higher sensitivity to wax-induced ageing. These findings highlight fibre length- and material-specific responses of traditional handmade papers to waxing followed by stone-calendering, providing empirical data to inform paper conservation practice and guide the refinement of this traditional processing method in calligraphy/painting mounting crafts and processed paper production – by balancing calendering immediate aesthetic benefits with wax-induced impacts on long-term structural and ageing integrity, with all effects being subtle, fibre length-dependent, and within experimental uncertainty.