Sustainability, access and process: A discussion about collection environments

There's an unspoken but underlying assumption in preventive conservation that our role is to make things last as long as possible. I'm not sure we should consider ourselves in charge of how long things last. We should be in charge of interpreting, explaining, and managing the life expectancy and longevity of objects

Sustainability, access and process: A discussion about collection environments

There's an unspoken but underlying assumption in preventive conservation that our role is to make things last as long as possible. I'm not sure we should consider ourselves in charge of how long things last. We should be in charge of interpreting, explaining, and managing the life expectancy and longevity of objects

Shrinkage and mechanical properties of drying oil paints

[EN] Understanding how the evolving molecular composition of an oil paint layer on its transition to an aged solid film affects its dimensional change and mechanical properties is fundamental to the assessment of material durability and more broadly risk of degradation of oil paintings. Tensile properties-modulus of elasticity and strain at break-as well as cumulative shrinkage were determined for a selection of oil paints from Mecklenburg¿s Paint Reference Collection now after approximately 30 years of drying. The oil paints were found to get stiffer and more brittle with diminishing plastic deformation and increasingly elastic behaviour. For some paints, the increases in stiffness and decreases in the strain at break were dramatic during the late stage of drying. The observations modify the current physical model of paintings in which the mismatch in the response of glue-based ground layer and unrestrained wood or canvas support to variations in relative humidity (RH) has been identified as the worst-case condition for the fracturing of the entire pictorial layer. This study demonstrated that some paints were more brittle than the glue-based ground layer and as a consequence more vulnerable to cracking. The shrinkage of paints due to molecular relocation and/or evaporation of organic medium as they dry and age was measured. This shrinkage can exceed their strain at break and lead to fracturing of the oil paint layer if it is restrained by a dimensionally stable substrate. Consequently, after long-term drying, the cumulative shrinkage can cause oil paints to crack even in absence of fluctuations in RH or temperature. An example of cracking developed in an oil paint layer on the top of an undamaged ground layer in a historic panel painting was made evident by the X-ray microtomography.This work was funded by the European Union's Horizon 2020 research and innovation program under grant agreement No. 814624 and the statutory research fund of the Jerzy Haber Institute of Catalysis and Surface Chemistry Polish Academy of Sciences. Lukasz Bratasz's work was financed by the Polish National Agency for Academic Exchange, project Polish Returns [Grant PPN/PPO/2018/1/00004/U/00001].Janas, A.; Mecklenburg, M.; Fuster-López, L.; Kozlowski, R.; Kékicheff, P.; Favier, D.; Andersen, CK.... (2022). Shrinkage and mechanical properties of drying oil paints. Heritage Science. 10(1):1-10. https://doi.org/10.1186/s40494-022-00814-211010

Mechanical properties and moisture-related dimensional change of canvas paintings¿canvas and glue sizing.

[EN] Understanding canvas paintings as physical systems is fundamental to develop evidence-based environmental specifications for museums. A number of tests were carried out to determine mechanical properties of canvas, canvas sized with animal glue and animal glue-based ground layer (gesso) as a function of relative humidity (RH). The mechanical properties of the canvas samples tested exhibited an anisotropy dependent on the measurement direction, being the stiffness corresponding to the weft direction greater than the warp and diagonal ones. Sizing the canvas with a layer of animal glue significantly increased its modulus of elasticity while the anisotropy of mechanical properties was kept in the composite material. The application of an animal glue-based ground layer on sized canvas increased the elasticity modulus of the system by another order of magnitude (similar to 2 GPa) whereas the anisotropy of the material disappeared. The measurements were carried out in a wide range of RH from 30 to 90%. An increase in RH caused a decrease in the material stiffness. Cracking of the gesso layer, which is often responsible for the formation of cracks in paintings, was observed at strains of the order of a few thousandths. Swelling of glue sizing dominated the moisture-induced swelling of the composite material in the less stiff warp direction, completely overriding the shrinkage of the untreated canvas. In contrast, the swelling of the composite material in the stiffer weft direction was much smaller than for pure glue alone, being clearly affected by the textile.This work was funded by the European Union's Horizon 2020 research and innovation program under grant agreement No. 814624 and the statutory research fund of the Jerzy Haber Institute of Catalysis and Surface Chemistry Polish Academy of Sciences. Lukasz Bratasz's work was financed by the Polish National Agency for Academic Exchange, project Polish Returns [Grant PPN/PPO/2018/1/00004/U/00001]Janas, A.; Fuster-López, L.; Andersen, CK.; Vicente-Escuder, Á.; Kozlowski, R.; Poznanska, K.; Gajda, A.... (2022). Mechanical properties and moisture-related dimensional change of canvas paintings¿canvas and glue sizing. Heritage Science. 10(1):1-10. https://doi.org/10.1186/s40494-022-00794-311010