A mechanical study on the conservation of bookbindings

To enhance the rationale behind the materials and crafting choices made by book conservators, a mechanics-of-materials approach has been applied to evaluate the strain on the spine of bookbindings during opening and to characterise the materials used in their conservation. Several different kinds of thread were tested in uniaxial tension until failure to identify the characteristics associated with strong and durable threads. The same threads were also subjected to cyclic uniaxial tension loading, simulating the forces applied by conservators during sewing, to investigate the causes of thread break in this process. Flat and twisted alum-tawed skin double thongs, which support the sewing thread on the spine, were also tested in uniaxial tension and their mechanical behaviour was compared to that of a linen cord commonly used for the same purpose. The linen cord demonstrated significantly higher stiffness and strength than the alum-tawed skin thongs, making it a more suitable choice for spine support. Additionally, the strain on the book spine was evaluated when the book was in an open position. Using stereo-correlation techniques, compression vertical bands of several percent were observed. This quantitative analysis goes beyond the simple bending models previously reported in the literature as it accounts for the specific structural complexity of codex structures.