A Parametric Analysis of Relative Humidity Effects on Traditional Panel Paintings
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A Parametric Analysis of Relative Humidity Effects on Traditional Panel Paintings 1
Eric Hagan, 2Evan Quasney, 2Marion Mecklenburg Art Conservation Program, Queen’s University, Kingston, ON, Canada 2 SCMRE, Smithsonian Institution, Washington, D.C., U.S.A 1
ABSTRACT A finite element analysis was performed on panel painting structures subjected to changes in relative humidity. Measured Young's modulus values and humidity expansion coefficients were used to define the properties of materials characteristic to northern and southern European panels. Models of northern panels simulated white oak with two layers of oil paint, while models of southern panels simulated cottonwood with gesso and two oil paint layers. In both cases, the properties of the oil paints were input for lead white and Naples yellow respectively. Influence of radial/tangential grain orientation, panel thickness, and structural support were investigated through various humidity changes. Results are presented in the form of stress in the wood, gesso, and paint layers as well as curvature of the painted surfaces. Methods of reducing panel curvature with structural support are discussed, which involve applying a frictionless cradle, wood battens, or verso gesso layer. Verification of the model was performed with a derivation of general stress equations for a cradled painting with no friction between the slider-bars and the panel. A comparison of derived and parametric results confirms accurate behavior of the model. INTRODUCTION Finite element analysis (FEA) is a powerful tool used in a wide range of mechanical and civil engineering applications. Software packages are specifically designed for structural mechanics as well as heat transfer and fluid mechanics. Little work has been performed with FEA on works of art due to the need for measured material properties. In the scientific analysis of art and archaeology objects, the use of FEA has largely been confined to the study of load distributions in historic buildings [1,2]. Years of research at the Smithsonian Center for Materials Research and Education (SCMRE) have provided the means for developing accurate finite element models of a wide range of artistic works. Material properties such as Young’s modulus, thermal expansion coefficient, and moisture expansion coefficient are now defined for various woods, gesso formulations, oil paints, acrylic paints and many others. Mecklenburg [3] has described the method for determining the material properties required for finite element models. A previous analysis with this method has illustrated the stresses that develop in photographs and fabric supported paintings [4]. In this paper, the application of FEA has been extended to an investigation of relative humidity effects on panel paintings. The method for determining material properties and constructing computer models is identical to that shown in former work [2,3]. A brief description of the technique is presented here, and further background information is readily available from FEA and mechani
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