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Mechanical damage in oil paintings on canvas show up as cracks and loss of original paint. Several parameters can contribute to this type of degradation. These paintings have a complex layered structure, typically composed of minimum four or more hygroscopic materials, each of which has different (non-linear) material properties and geometrical com...
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... This faster degradation might be due to the absence of additives in the selected paint systems by Golden Artist Colours ( Figure S11-14). It has been reported in the literature that the peak at 150°C changes its amplitude over time due to the decrease in hydroperoxide concentration 67 . In the samples analysed after 6 months, it is indeed possible to observe that the peak is less resolved and broader compared to the curves observed after 4 days and 3 months. ...
The study of film-formation processes of oil paints has been extensively addressed over the last decade and the influence of metal ions in the drying and degradation stages of oil paints has been demonstrated. This research aimed to determine a suitable methodology for monitoring the early drying stages of selected commercial oil paint films and to gain an insight into the migration mechanisms of material degradation taking place between adjacent paint films, with special attention to the influence of the lead white. For this purpose, a hybrid approach was adopted to characterize the composition of the paint and highlight failure mechanisms in the paint films through a wide range of time. The methods included scribe tests, percentage weight variation (ΔW%), attenuated reflectance Fourier transform infrared spectrophotometry (ATR-FTIR), gas chromatography-mass spectrometry (GC-MS), and thermal analysis with differential scanning calorimetry (TG-DSC). The results show how metal ions interact with the oil binder and the pigment in the adjacent paint film: the transverse migration of lead white is shown to affect the reactivity of polyunsaturated triglycerides, increasing the rate of oxygen uptake and promoting the formation of radicals and bonds between polymer chains, depending on the pigment with which it interacts.
... Mecklenburg et al. [14] , Erhardt et al. [15] , determined stress-strain curves at various relative humidities for cottonwood and panel paintings studying mechanical and dimensional properties of their constituent materials, to suggest allowable safe fluctuations. Recently Lee et al. [16] developed finite element and extended finite element models of canvas paintings with different layer compositions and thickness variations and accounted for developed strains in respect to RH changes. In addition, Janas et al. [17] studied the degree of resilience of paintings preserved in specific microclimates as most paintings' manifest natural increase of stiffness and lower breaking strains due to their ageing process. ...
Environmental variations of Temperature (T) and Relative Humidity (RH) in air cause a superficial and/or sub-surface deformation (shrinkage/swelling) of organic hygroscopic objects, as for example wood. These environmental variations may be due to the natural variability of climate, to the use of Heating, Ventilation and Air Conditioning (HVAC) systems and to the presence of people. This contribution focuses on a group of wooden rural churches located in harsh climates in Sweden. The churches, which are still in use for the local communities, are heated during wintertime to reach acceptable indoor comfort levels causing potentially risky T and RH fluctuations for hygroscopic objects. In this framework, the main goal is assessing the risk of fracture on wooden structural elements caused by hygrothermal fluctuations. The method is based on a preliminary approach for reconstructing the climate history experienced by a typical wooden structural element of these churches and that, over time, results in a cyclic fatigue loading, naturally induced by the outdoor climate. Then, the effect of the artificial heating on the indoor mi-croclimate and, therefore, on the reconstructed fatigue curve is assessed. Main outcomes were obtained by using a methodology that is preliminary based on simplifying assumptions, due to a severe lack of knowledge, in literature, about the fatigue behavior of wood. Finally, main considerations on the fatigue behavior of exposed wooden elements are drawn up, namely the estimation of their residual life (or "life-to-damage"), which may support conservators or church managers in better managing the microclimate to reduce the risk of fracture on valuable objects.
... The implementation of tight climate control is usually difficult, particularly in historic buildings, and involves energyintensive air-conditioning systems. Evidence-based, more relaxed environmental specifications [5][6][7] have been made possible by studies investigating the moisture and mechanical response of materials and their assemblies, as well as the critical levels of stress/strain at which the materials began to deform plastically or fracture [8][9][10][11][12][13][14][15][16][17][18][19][20]. A laminar model of paintings subjected to variations of RH was proposed [1]. ...
The fracture toughness in opening mode GIc for selected oil paints from Mecklenburg's Paint Reference Collection after approximately 30 years of natural ageing was determined using the procedure adopted from the ASTM D5528–13 standard in which double cantilever beam specimens are split in tensile tests. The careful reglueing procedure allowed multiple fracturing tests to be carried out that not only improved statistics of the measurements but also provided insight into the variation of the fracture toughness across the paint film observed for some paints. The latter was due to pigment sedimentation or chemical change of the oil binder as a result of the easier access of oxygen from the side open to the air. For the lead white paint, used over centuries both in paint films and oil grounds, the GIc values more than doubled from 18 to 39 J/m² for three consecutive cracks formed at an increasing distance from one side of the paint film. The study demonstrated that fracture toughness corresponding to the first crack formation in aged oil paints ranged between 10 and 40 J/m², relatively low values compared to the animal glue-based ground in paintings. In consequence, oil paints are more vulnerable to crack initiation and growth induced by tensile stress than the ground layer. The measurements filled the gap in the knowledge required for the analysis of fracturing or delamination processes in paintings.
... New tools for processing and analysing air quality data in museums were reported providing key risk indicators for calculating risk levels for specific heritage materials such as canvas painting [31]. Computerised modelling of degradation phenomena in model canvas paintings observed in real case studies was developed as a function of T and RH fluctuations [32]. Supervised machine learning methods were also used to predict the environmental risks of heritage collections in historical buildings [33]. ...
The impacts of climate change on heritage collections in Mediterranean museums are serious and lead to accelerated material degradation, loss of value, increasing conservation costs and climatisation. Climate change scenarios and simulation models have been developed to predict the extreme and average future environmental conditions and to assess the future long-term risks caused by global warming for museum buildings and their collections in Mediterranean countries, with Egypt being particularly at risk. This paper presents the results of the risk analysis of the indoor and outdoor environments in Alexandria Museum of Fine Arts (AMFA) in Egypt to provide an overview of the current situation of conservation and museum management and to provide evidence-based data to support decision-making regarding preventive conservation given the museum's limited funding, capacity and resources. Unfortunately, the air quality in the museum cannot be considered satisfactory and specific measures need to be taken to improve the level of air quality and museum and building management. The results enabled an assessment of indoor air quality and provided information on potential risks to the museum building and collections, including variations in temperature (T) and relative humidity (RH), concentrations of NO2, SO2, O3, CO2, acetic and formic acid and lighting conditions, as well as the location and management of the museum. The results necessitate the development of a preventive conservation plan to address the challenges associated with high T/RH fluctuations and pollution pressure. This requires more regular use of the HVAC system within certain T/RH set points as well as minimising light exposure and the use of UV-filtering glazing. Care should be taken to ensure that housekeeping and emergency preparedness reduce the damping and salt florescence in the museum building. However, dealing with the impact of climate change on indoor and outdoor environments and museum collections in Mediterranean museums requires a holistic and adaptive approach that includes joint collaboration, research, training and strategic planning to ensure the long-term preservation of valuable cultural heritage collections in different climates with customised adaptations based on local environmental conditions, resources and needs. Resilience planning should be region-specific and take into account the potential impacts of extreme weather events, sea level rise and other climate-related challenges.
... In relation to canvas paintings, Lee et al. [4] explore three degradation phenomena in model canvas paintings under desiccation (bulging formation around the corners, crack formation in glue and ground layers, and, finally, plastic deformation in the ground and oil paint layers) through finite element method (FEM) and extended-FEM (XFEM) computer models. The results showed that the geometrical deformation of the stretcher was a result of the shrinkage of the glue, which reduced the tension stress in the centre of painting. ...
... Less humid conditions, while seemingly advantageous for the protection of timber heritage from biological damage, would likely mean that wooden objects equilibrated to high humidity would lose water and contract. This could lead to cracks or the disruption of surface coatings [63,88]. In addition, shifts in seasonality can affect the times popular for visits and therefore might require adjustments to site management [89]. ...
Timber heritage sites are vulnerable to damage from moisture. Simple meteorological descriptions of climate need to be tuned to capture drivers that threaten heritage, including dimensional change, insect attack and mould growth. Global climate models often provide projections through to the end of the 21st century but need to be translated to a local level to reveal processes of deterioration at specific sites. Translation to a local level can be challenging and requires the use of local information from a range of sources. This translation is explored over a range of sites facing different climate pressures, including fungal and insect risk at Harmondsworth Great Barn, England; changes in humidity range, salt risk and algal growth in rural timber buildings in the Midwestern states, USA; wind-driven rain impacts on board houses in Freetown, Sierra Leone; and rainfall and humidity range on timber buildings among the tropical rainforests of the Amazon, Congo Basin and Southeast Asia. Evidence-based narratives provide a tool to incorporate a multiplicity of local information to enrich projections and the interpretation of the model output. These could build trust and aid decision-making based on future projections, which are inherently uncertain.
Oil paintings are complex, multi-layered systems that are prone to chemical degradation. While it is increasingly recognised that water plays an important role in these degradation reactions, little is known about moisture concentrations in oil paint systems and their temporal variation in response to fluctuating ambient air humidity. This knowledge is necessary to further preventive conservation, specifically to establish optimal environmental conditions to safeguard works of art for future generations. We developed a transient one-dimensional moisture transport model based on Fickian diffusion enabling the integration of experimentally recorded relative humidity data. Moisture sorption and transport data for painting materials have been reviewed from literature showing that each component of a painting has rather distinct properties. Including the properties of the individual layers enabled predicting the behaviour of a multi-layered painting system. A sensitivity study indicated that the response of a multilayer is determined by the combination of diffusion coefficients, isotherm shapes, maximum water contents, layer thicknesses, period of RH fluctuation and stacking order of the layers. Finally, the model was employed to investigate a case study of 18th-century painted wall hangings in a historic house to illustrate the insights that can be gained from this approach and the types of conservation-related questions that can be answered.
