Gels are transversal materials with key applications in multiple scientific and technological sectors, including the preservation of Cultural Heritage that is a fundamental drive for socioeconomic resilience. Recently, the new class of twin-chain (TC) polymer gel networks was developed, using freeze-thaw (FT) cycles on solutions of polyvinyl alcohol (PVA) with two different hydrolysis degree and molar mass. Taking advantage of polymerpolymer phase separation in the pre-gel solutions, a sponge-like, interconnected porosity is templated in the hydrogels during FT, which concurs to boost the cleaning capability of the gels versus soil and aged coatings that jeopardize paintings and other iconic artworks. This review covers the latest developments in this new class of gels, and their use in the conservation of works of art. The TC gels allowed time-effective restoration of masterpieces (paintings by Picasso, Pollock, Lichtenstein), which would have been risky and time-consuming with conventional restoration materials in wet cleaning. The review discusses gelation mechanisms, the partial replacement or decoration of PVA with non-toxic synthetic or bio-based polymers, the counterintuitive role of gels' tortuosity in the cleaning process, and the upload of these gels with nanostructured cleaning fluids (microemulsions, micelles). Overall, the TC PVA hydrogels constitute an advanced tool to preserve Cultural Heritage and transfer it to future generations; moreover, they represent a class of sustainable soft matter materials with potential impact in several fields, spanning from detergency to the cosmetic, pharmaceutical and food industries, tissue engineering, and others.

The recurrent crystallization and subsequent volumetric expansion of soluble salts pose significant risks to earthen sites, particularly those with archaeological remains on their surfaces. Therefore, timing interventions based on salt content is crucial. This study focuses on the effects of soluble salt content on the earthen site within the burial pits of the Qin Mausoleum, with a particular emphasis on defining safe salinity levels. A mixture of Na2SO4/NaCl salts in a 1:1 mass ratio was added to remodelled soil cakes, which were then aged in a climate chamber for several months. The area of salt expansion on the soil cakes' surfaces was measured using a deep-focus microscope to assess damage. The results indicate a sudden increase in salt expansion when salinity exceeded 0.1%. Additionally, re-evaluations of these soil cakes years later allowed for the exploration of mechanisms and the feasibility of assessing soil surface expansion and friability at different stages of the earthen site's lifecycle, including excavation and display. These findings provide preliminary scientific bases and novel methodologies for the further preventive conservation of heritage earthen sites.

The Great Wall is a world-renowned cultural heritage site and a national key protected cultural relic in China. The plants on the top surface of the Great Wall heritage site are one of the factors leading to the occurrence and continuous deterioration of the Great Wall. Therefore, there is ongoing academic controversy on how to scientifically dispose of the plants on the top surface of the Great Wall heritage site. Taking Beijing Dazhuangke Great Wall as an example, the preliminary field research was completed. This paper further describes the key technology for the disposal of remaining roots after removing the ground part of the plants from the top surface of the Great Wall heritage site and clarifies the basic idea of using the original covered soil on the top surface of the Great Wall heritage site, back-filling the original covered soil stripped via reparation of the layers and the regenerated plants in a seed bank to create 'soft capping' protection. This study provides a basic framework for 'soft capping' on the top surface of the Great Wall heritage site and construction of the cultural landscape of the 'Garden on the Great Wall'.

Safe and efficient conservation of cultural artifacts requires preventing artifacts deterioration and energy-saving environmental control. To achieve this, predicting deterioration caused by environmental conditions is necessary. Predicting the mechanical damage caused by humidity fluctuations necessitates knowledge of the mechanical properties of cultural artifacts materials. Although the mechanical properties of several artifacts have been extensively studied, no investigations have focused on the soils underlying wall paintings. This study aims to clarify some mechanical properties of the upper- and middle-coat soils serving as the substrates for Hiten wall paintings at Horyu-ji Temple. Mock-up materials were prepared, and splitting tensile and uniaxial compressive tests were performed. Simultaneously, specimens with various equilibrium humidities were tested to clarify their humidity dependency. The tensile and compressive strengths, Young's modulus, proportional limit, and Poisson's ratio of the upper-coat soil were 0.103-0.239 MPa, 1.16-2.55 MPa, 0.115-0.209 GPa, and 1.10-2.49 MPa, and 0.152, respectively. Moreover, the humidity-induced strains for the upper- and middle-coat soils were measured, and the moisture expansion coefficients were approximately 1240 and 2337 mu ST/-, respectively. The results of this study provide vital data for the conservation of the wall paintings and contribute to a deeper understanding of wall soil properties.