ScienceShot: How to Save Your Scroll

Along the River During the Qingming Festival; Photograph taken by Baidu Tieba/ Wikipedia Commons

ScienceShot: How to Save Your Scroll

Thomas is a news intern at Science.

Unlike books, curling up with a good scroll is a bad thing. Long-term storage of bound scrolls can cause the edges of the paper to twist outward, potentially tearing fibers and fading ink. Curators have traditionally blamed the deformation, known in Chinese as Qi-Wa, on humidity and imperfections in the scroll’s construction, but the biggest culprit is the flexible backing layer that the ornate top layer is mounted on, according to a mathematical formula reported this month in Physical Review Letters. When a scroll is rolled, the backing layer stretches to accommodate bending while the decorated top layer compresses, creating a difference in elasticity over time. Once unfurled, the backing layer’s resting length is now longer than that of the top layer. Because the two layers are attached together, the bottom layer pushes outward while the top layer pulls inward, causing the scroll’s sides to deform and curl up. The researchers inspected the curling on the ancient Chinese scroll Along the River During the Qingming Festival (pictured), which illustrates the daily lives of different social classes during the 11th and 12th centuries. The team went on to test its theories on cheaper and less historically significant sheets of plain copy paper and plastic film. Because art restorers often replace the scroll backing as part of restoration, the scientists recommend aligning the paper fibers in the backing along the scroll’s long edge, increasing the rigidness and reducing the amount of stretching when rolled. Alternatively, using a stiff brush to loosen the fibers along the middle section of the backing—like a meat tenderizer softens meat—will reduce the horizontal pull that causes curling. The team saw similar results when testing their techniques on their plastic film, suggesting that the methods could be used on flexible electronic paper displays, which also curl when rolled.

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Posted in Math