Abstract
Panel paintings—complex multi-layer structures consisting of wood support and a paint layer composed of a preparatory layer of gesso, paints, and varnishes—are among the category of cultural objects most vulnerable to relative humidity fluctuations and frequently found in museum collections. The current environmental specifications in museums have been derived using the criterion of crack initiation in an undamaged, usually new gesso layer laid on wood. In reality, historical paintings exhibit complex crack patterns called craquelures. The present paper analyses the structural response of a paint layer with a virtual network of rectangular cracks under environmental loadings using a three-dimensional model of a panel painting. Two modes of loading are considered—one induced by one-dimensional moisture response of wood support, termed the tangential loading, and the other isotropic induced by drying shrinkage of the gesso layer. The superposition of the two modes is also analysed. The modelling showed that minimum distances between cracks parallel to the wood grain depended on the gesso stiffness under the tangential loading. Despite a nonzero Poisson’s ratio, gesso cracks perpendicular to the wood grain could not be generated by the moisture response of the wood support. The isotropic drying shrinkage of gesso produced cracks that were almost evenly spaced in both directions. The modelling results were cross-checked with crack patterns obtained on a mock-up of a panel painting exposed to several extreme environmental variations in an environmental chamber.
Highlights
As discussed in detail in a recent paper on fracture processes in paint layers on wood (Bratasz et al 2020), the material served for centuries as a support for paintings in Europe
Paintings on the wood are complex multi-layer structures composed of wood support sized with animal glue and a paint layer consisting of a preparatory layer of gesso—a mixture of animal glue and white inert solid—to produce a smooth painting surface, and paints and varnishes on the top
After a few relative humidity (RH) cycles, the gesso layer was covered with a dense network of cracks, which stabilized after approximately 15 cycles, so no further crack development was observed in the last five cycles
Summary
As discussed in detail in a recent paper on fracture processes in paint layers on wood (Bratasz et al 2020), the material served for centuries as a support for paintings in Europe. All materials constituting painted wood are humidity sensitive: they swell when they gain moisture and shrink when they lose it, which generates moisture-induced stresses owing to materials’ different dimensional responses to the loss or gain of moisture. Wood is anisotropic and its moisture-related dimensional changes vary in its three principal anatomical axes—longitudinal, or parallel to the grain, radial, and tangential. The most pronounced moisture response is in the tangential direction, and it halves in the radial one. Wood can be considered dimensionally stable parallel to its grain
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
