Three-dimensional numerical and experimental study of fracture saturation in panel paintings

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.

Fracture toughness of dried oil paints

“…The origin of environmental speci cation for paintings, and in general for museums' collections was thoroughly analysed in several publications (3,4,5). As one of the authors of this publication described in the latter article, until the beginning of the 1990s, the environmental speci cations were based on the technical capabilities of climate control systems rather than experimental or theoretical evidence of collections' needs.…”

Effects of nonlinear moisture coefficients of expansion on rectangular Craquelure of oil panel paintings

“…These are occasionally reinforced by stochastic components representing thermal or instrumental noise. Through the crack growth, many mechanisms are included and studied such as thermal heating by energy release of crack formation [5], heating energy in museums or climate changes [6], and fracture saturation [3,7]. A painting is not at, and they are super thin sculptures.…”

“…The conservator of Girl with a Pearl Earring [4] describes how they analyzed all the cracks in the painting, spotting where the painting might've been pressed or where restorers screwed up. Jamalabadi et al [7] suggested that gesso and unrestrained wood substrate's responsiveness to variations in relative humidity is the most dangerous condition for cracking a panel painting. Various pigments and driers could be considered for example lead white lead, white with litharge, zinc white, sap green, Verdigris, red iron oxide, malachite, and synthetic ultramarine.…”

Hierarchical craquelure patterns in paintings on panels

“…This is the third of a series of papers analysing a model of panel paintings to elucidate the structural response of their pictorial layers with a network of cracks under environmental loadings [1,2]. The issue is of key importance in developing evidence-based environmental specifications for museums and historical buildings as panel paintings are amongst the objects most vulnerable to relative humidity (RH) and temperature fluctuations.…”

“…In the most recent study, environmentally induced stresses in the gesso layer were analysed, as cracking of this layer, resulting from the mismatch in the moisture response of gesso and wood, inevitably leads to cracking of the entire pictorial layer [2]. Wood is anisotropic and its moisture-related dimensional change varies in its principal anatomical directions: longitudinal -or parallel to the grain, radial, and tangential.…”