Craquelure Pattern Research Articles

Development of craquelure patterns in paintings on canvas

Canvas paintings are layered structures composed of canvas support sized with animal glue, a preparatory layer of the ground, and paint and varnish layers on the top. Preventing or limiting humidity-induced stresses in these structures requires an understanding of the relevant processes and risks. A three-dimensional model of a canvas painting was used to analyse stresses and crack development in the two-layer structure comprised of a glue-sized canvas on a wooden stretcher with a layer of stiff chalk-glue ground representing a pictorial layer in historic canvas paintings. The model was subjected to a large relative humidity fall which induced shrinkage of the glue-sized canvas. The modelling revealed that when a stretcher with flexible wooden bars is considered, high tensile stresses arise in the ground layer at the corners of the painting, and cracks are formed in these areas in the direction perpendicular to the painting’s diagonal. Ratios of critical distances between cracks to the ground layer thickness for which stresses in the midpoints between the cracks dropped to below the level inducing fracture in the material were estimated for various magnitudes of the relative humidity drop and thicknesses of the ground layer. Increasing ground layer thickness limits the hygric response of the sized canvas and makes the paintings less vulnerable to humidity variations. The ratio of stress along the diagonal calculated for painting with one crack to the solution without cracks was described by the double Lorentz function. A simple procedure of calculating stress variations along the diagonal—using the function—on a sequential addition of cracks was developed. Cracks in central parts of canvas painting were found to be induced by permanent cumulative drying shrinkage of the oil-based paints and grounds due to the evolution of the molecular composition of the oil binder. The outcome of the modelling indicated that the risk of cracking of the pictorial layers in canvas paintings due to drops in ambient relative humidity was small.

Development of craquelure patterns in paintings on panels

Panel paintings are multi-layer structures composed of humidity-sensitive materials. Preventing or limiting stresses in these structures, generated by the loss or gain of moisture, requires an understanding of the relevant processes and risks. A three-dimensional elastic model of a panel painting was used to analyse surface stresses and understand how crack patterns are developed in the two-layer structure of the pictorial layer—the gesso and the paints. Two historically important paint types were considered—egg tempera and oil paints, laid on a gesso produced following historical procedures. Two scenarios of stress development were analysed: permanent cumulative drying shrinkage of paints or gesso, owing to gradual loss of water or evolution of the molecular composition of the binders, and moisture-induced cyclic swelling of the wood substrate. Ratios of distances between cracks in the tangential and longitudinal directions of a wood panel to the layer thickness were estimated for increasing magnitudes of materials’ dimensional change in the two scenarios. The critical values of the ratios for which stress in the midpoint between the cracks dropped below the value inducing strain at break in the materials and saturation of the crack patterns occurred, was approximately 3–4 or 5–6 for the paints and the gesso, respectively. The critical distance normalized to the gesso thickness between cracks parallel to the wood grain induced by cyclic swelling of the wood substrate due to relative humidity variation in the range of 50–70% was 6. The study demonstrated that crack spacings in the fully developed crack systems remain sensitive only to the thicknesses of paint or gesso layers which, therefore, can be derived from the crack pattern geometry. Existing flaws in gesso were found not to increase the risk of new crack development.

Combining engineering and wood science for the conservation of artworks: Hygro-mechanical study of Mona Lisa’s wooden support

Since 2004, the wooden support of Mona Lisa has been studied by an international research team formed by specialists of wood science and optical measurements, interacting closely with curators and restorers, to evaluate the climatic specifications adopted for the then new climate-controlled display case, assess the risk of propagation of a historical crack affecting the Panel, suggest possible improvements to the Panel’s framing, and improve the technological aspects of the current monitoring procedure. The study has been carried out mainly by direct observation and measurements during the yearly opening of the display case, by continuous monitoring of the Panel’s mechanical behaviour and by developing a predictive numerical model based on the finite element method. This paper deals with the following topics: (i) a technological description of the Panel and of its framing, (ii) the non-invasive measurement equipment and monitoring methods developed, (iii) the simulations of the hygro-mechanical behaviour, (iv) the most significant results obtained so far, including the derivation of the elastic parameters of the wooden Panel, the description of the contact zones between Panel and framing, the evaluation of contact forces and possible actions for improving the framing. The model implementation evidences the correspondence between principal strains in the Panel and craquelure patterns in the paint layers, and allows assessing the crack propagation risk.

Investigation of craquelure patterns in oil paintings using precise 3D morphological analysis for art authentication.

The development of scientific technology for art authentication has elicited multidimensional evidence to distinguish forgeries from original artwork. Here, we analyzed the three-dimensional morphology of cracks that contain information, such as the painting features of artworks, using optical coherence tomography. The forgeries were produced by an expert from original oil paintings with cracks that occur owing to paint drying, canvas aging, and physical damage. Parameters, such as shape, width, and depth, were compared based on the cross-sectional images of the original and fake cracks. The original cracks were rectangular and inverted, but the fake cracks were relatively simple inverted triangles. The original cracks were as deep as the thickness of the upper layer and mostly were “thin/deep” or “wide/shallow”. The fake cracks were observed to be “’thin/shallow” or “wide/deep”. This study aims to improve the understanding of crack characteristics and promote the development of techniques for determining art authenticity.

Optimal rectangular crack pattern based on constructal, fracture saturation, and energy minimization theories for painting on wood

The knowledge of how the craquelure happens and their pattern on historical objects especially paintings are interested in the field of cultural heritage. In this paper, optimal rectangular patterns are calculated based on current theories for a fully anisotropic model of wood and an anisotropic model of gesso annealing shrinkage. First, the constructal theory is applied which is responsible for the crack growth at the beginning periods of drying the produced painting. As the constructal theory is based on greater access to the drying currents that flow through the crack pattern, the compromise of two mechanisms of diffusion of moisture content and advection drying by fluid flow through the cracks detect the optimal scale of rectangular patterns. A rectangular two-dimensional solid is dried by the diffusion mechanism and advection boundary condition. The resulted shape is found by the intersection of two limits of many cracks (dense crack by high advection) versus a few cracks analytically. Then a parametric study is done to find the optimal distance between blocks of crack islands numerically. Second, the fracture saturation mechanism in long-term climate changes is applied to find the possible rectangular pattern which can appear based on the fact that positive stress should exist in the middle of the crack island to create a new crack. Finally, the strain energy density approach for various fracture strengths is examined to predict the optimal rectangular shape. The numerical results are compared with existing experimental results and previous works demonstrate the capability of the above-mentioned models. The method and results could be generalized for the other types of craquelure patterns and structural conservators.

New concept for art and antiquities identification based on craquelure pattern analysis

In this paper, it is shown that the craquelure patterns of paintings and other antiquities can be considered as fingerprints so that the authenticity of any given artwork can then be verified against prior works. The authors propose to extract craquelure features from photographic images and use them in the implementation of a unique matching procedure to address the art forgery issue as well as to monitor the health conditions of the objects concerned. This feature extraction strategy is robust against illumination, scale, rotation and perspective distortion. The craquelure extraction system developed, called multi-scale multi-orientation morphological processing (MMMP), performs analyses in each sub-band. A comprehensive craquelure image dataset has been constructed from a variety of different types of painting and other art objects. The results show significant improvement and compare favourably with the current best results in the market.

Mechanism of craquelure pattern formation on panel paintings

The drying shrinkage accumulation from exposure of freshly prepared gesso layers to relative humidity (RH) cycles was determined to elucidate the mechanism of craquelure pattern formation on panel paintings. The progresive drying shrinkage of the gesso is observed only under the cycles going to high RH levels which bring about transitions from brittle to ductile state of the material. The first incidence of fracture on the gesso layers occurred after a limited number of cycles ranging between a few and 100 for a range of layer thickness between 0.5 and 1 mm. The craquelure patterns stabilised also after a limited number of cycles (30 for the 1-mm thick layer). Upon increase in the gesso layer thickness, the strength of the layer is reduced and the spacing of shrinkage fractures increases. The study demonstrated that craquelure patterns, mimicking historical ones, can be realistically produced in laboratory conditions. Such studies would provide useful information for preparing specimens simulating historic panel paintings and would inform the current efforts on automatic, computer-aided classifications of crack formations on paintings.

Craquelure structure of protein film modification under the laser radiation of different spectral range action

A craquelure structure of protein film as indicator of macromolecule state is discussing. Craquelure is a network of fine cracks or crackles on the surface of a painting, caused chiefly by shrinkage of paint film or varnish. The actions of laser radiation in the red and green spectral region on the protein film craquelure structure by the example of albumin are considering. It is experimentally shown that after drying the protein layer a craquelure pattern (variety of cracks in the layer) is formed with the parameters strongly modified by the laser action and depending on the wavelength of radiation and the time (energy density) of exposure.

Identification, Analysis, and Elimination of Craquelures in Old Oil Painting Images

In this study, an integrated approach to identifying, analyzing and eliminating craquelures in high resolution oil paintings in images is proposed. It starts by identifying the craquelure networks in the oil painting via utilizing morphological top-hat operator, and follows by running a newly-devised crack line tracing algorithm to obtain properties of all the individual crack line segment such as the length and orientation. Closed regions in the craquelure netowrks is subsequently searched to extract further information about the craquelure patterns. Then, an improved recursive median filters is proposed to carry out the virtual restoration of the oil painting. The study concludes by presenting the experimental results which demonstrate good performance on oil painting craquelure analysis and virtual restoration.

The development of a diagnostic method for geographical and condition-based analysis of artworks using craquelure pattern recognition techniques

The development of a diagnostic method for geographical and condition-based analysis of artworks using craquelure pattern recognition techniques

STATISTICAL FEATURE-BASED CRAQUELURE CLASSIFICATION

We demonstrate an automatic procedure for extracting features such as directionality of crack patterns, distribution of node distances and segment lengths, fractal dimension, entropy, and crack coverage to aid in automatic classification of painting cracks or craquelures. To test our classifier, we make use of four distinct craquelure patterns, designated by names based on their country of origin, namely: Dutch, Flemish, French or Italian. We report that selecting features based on effect size ratio from the above statistical measures, the standard linear discriminant analysis (LDA) can make predictive classification of the craquelure patterns with a 69.4% accuracy. Effect size ratio simultaneously quantifies the extent of correlation and variance of two statistical sets of data. This test set accuracy is more than two times better than mere chance classification, or the proportional chance criterion, computed to be ΦPCC= 27.61% and also twice the recommended classifier accuracy 1.25 × ΦPCC= 34.4%. We compare the result with the nonlinear method of neural network and we observe no marked improvement in the resulting accuracy. This suggests that the problem at hand with respect to the statistical features extracted is a linear classification problem. The work provides a comprehensive guide on the algorithms that can be used to extract quantitative information of crack patterns.