1991 Paintings - Their Response to Temperature, Relative Humidity, Shock, and Vibration (2025)

The Changing Mechanical Properties of Aging Oil Paints

MRS Proceedings, 2004

The stiffening and embrittlement of oil paints over time has been a real concern for those responsible for the long term care and preservation of paintings. This paper examines the effects of time, pigments, relative humidity (RH), temperature and solvents on the mechanical properties of traditional oil paints. In this way it is possible to determine the role of each factor in causing the paints to become brittle. Even after 14 years the oil paints show little evidence that the long term "maturing" processes have begun to slow down. It is shown that there seems to be little correlation between the time paint requires to "dry-to-the-touch" and the longer term mechanical properties. Both low and high temperature levels can increase the stiffness of the paints though the mechanisms are quite different. Considerable hydrolysis of the paints occurs early in their history and the ones that hydrolyze most quickly are the ones that remain the most flexible.

The Effects of Temperature and Relative Humidity on the Mechanical Properties of Modern Painting Materials

Mrs Proceedings, 1992

ABSTRACTThe mechanical properties of strength, modulus, and elongation to break were studied for artists' acrylic and alkyd paints under varying conditions of temperature and relative humidity (RH). In the ambient environment, 23° C, 50% RH, acrylic paints are very flexible and are able to sustain large deformations (>50%). Alkyd paints are much stiffer and stronger, and they cannot sustain deformations nearly as dramatic as the acrylics. Acrylic paints at 5% RH are stiffer and stronger than at 50% RH and their ability to stretch is lessened. At temperatures below 15° C at 50% RH, the strength and stiffness of acrylic paints begin to rise rapidly. Some were found to be brittle at 5° C, and by −3° C, all were brittle. At a lower RH, some acrylic paints became brittle at a temperature near 11° C. These temperatures and relative humidities may be found in the transport environment of art objects, and may render them subject to possible damage.

The mechanical behavior of artists' acrylic paints with changing temperature and relative humidity

Acrylic paints are commonly found in modern art. The mechanical properties of strength, modulus, and ability to elongate of a large sampling of artists' acrylic paints were studied in the temperature range of-8° C to 33° C, and from 5% to 50% relative humidity (RH). Data derived from the stress-strain curves suggests that acrylic paints lose the ability t o plastically deform in response to applied force below temperatures of 5° C at sot RH, and below 11° C at 5% RH. The brittle behavior of acrylic paints below these temperatures suggests a glass transition temperature that is RH dependent.

After the paint has dried: a review of testing techniques for studying the mechanical properties of artists’ paint

Heritage Science, 2021

While the chemistry of artists’ paints has previously been studied and reviewed, these studies only capture a portion of the properties affecting the response of paint materials. The mechanical properties of artists’ paints relate to the deformation response of these materials when a stress is applied. This response is dependent on many factors, such as paint composition, pigment to binder ratio, temperature, relative humidity, and solvent exposure. Here, thirty years of tensile testing data have been compiled into a single dataset, along with the testing conditions, to provide future researchers with easy access to these data as well some general discussion of their trends. Alongside the more commonly used techniques of tensile testing and dynamic mechanical analysis, new techniques have been developed to more fully investigate the mechanical properties, and are discussed along with salient results. The techniques have been divided into two categories: those that are restricted to ...

Shrinkage and mechanical properties of drying oil paints

Heritage Science, 2022

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.

Fracture toughness of aged oil paints

Heritage Science, 2024

The fracture toughness in opening mode G Ic 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 G Ic values more than doubled from 18 to 39 J/m 2 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/m 2 , 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.

(2023) Mapping damage from pigment-medium interaction in three neo-plastic oil paintings. In: Working Towards a Sustainable Past. ICOM-CC 20th Triennial Conference Preprints, Valencia, 18–22 September 2023, ed. J. Bridgland. Paris: International Council of Museums., pp.1-11

ICOM cc Valencia 2023, 20th Triennial Conference, 2023

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

Heritage Science, 2022

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 (~ 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 moistureinduced 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.

Investigating the conservation problems of oil paintings on paper supports

2017

The initial results of a research project on the investigation of problems presented by a collection of oil paintings on paper supports are presented. The project focuses on the effect of the oil medium on the deterioration of cellulose, on the materials and techniques used by the artists and on comprehension of the resulting problems. Non destructive methodology was used to record the behaviour of the materials when examined in several regions of the electromagnetic spectrum which gives an indication of areas of damage. . Various analytical techniques were applied to investigate the painting materials and supports in original works of art. The increase in rate of the oxidation of cellulose in paper, when the paper is coated in oil, is investigated by analyzing volatile organic compounds emitted during ageing tests. The assessment of the results obtained will act as a pilot for a more extensive program of research, the ultimate aim of which is the formulation of a recommended method...

Effect of thermal accelerated ageing on the properties of model canvas paintings

2000

The aim of this study is to develop a laboratory technique to simulate a natural ageing of canvas paintings adopting artificial ageing methods in air (thermal oxidation), in the absence of light. Four models of canvas paintings aged up to 315 years are considered. Paintings are constituted of oil film on oil ground layer, oil film on tempera ground layer, tempera film on tempera ground layer or by tempera film on oil ground layer. Surface strength and the colour of the paintings and the degree of polymerization (DP) of linen canvas were evaluated at different steps of ageing. The degradative result was estimated as the DP of linen canvas after prefixed times of microbial attack. © 2000 É ditions scientifiques et médicales Elsevier SAS Keywords: Canvas painting / oil film / tempera film / tempera ground layer / oil ground layer / degree of polymerization / degradation