Modern Non-destructive Physical Methods for Paintings Testing and Evaluation

There are several rapidly developing non-destructive physical methods that are increasingly used for the analysis and assessment of art objects. These technologies are posed to bring about drastic changes in the attribution and inventory characterization procedures carried out by museums, private collections, art dealers, and art community as a whole. Certainly today nondestructive evaluation (NDE) of art objects is becoming more and more sophisticated. The applications of these methods include but not limited to deterioration detection, authentication, revealing forgeries and fakes, and attribution. There are numerous physical techniques that are currently adopted for various tasks related to NDE in the art world, many of which have been specifically developed for particular applications of paintings evaluation. While some of these methods are well-known, others remain rather obscure. This article is an attempt to review a few physical techniques that could be successfully used for the conservation and authentication of paintings. The methods described here include multi-spectral illumination methods, thermographic techniques, scanning acoustic imaging, air-coupled ultrasound, Raman spectroscopy and imaging, and Mass-spectroscopy. INTRODUCTION It is perhaps appropriate at the outset of this review to describe the external factors which affect the condition of a painting. Certainly, the influence of temperature changes, exposure to light, inappropriate handling, bacterial contamination insect infestation, can contribute to changes in appearance and physical condition of a painting. Further, with such aging paint layers get more brittle leading to cracks or even the paint detachment from support. If left untreated, with time the painting can become unrecognizable or can even be irreversibly damaged. In order to properly preserve or restore a painting it is particularly important to know the physical/chemical mechanisms of degradation effects. The most common are: • Darkening and change of color – There are several possible reasons for color to change. The painting accumulates deposits of common room dust, soil particles, and particles of organic origin on its surface. Usually such deposits can be easily removed with wet cotton. Other mechanisms include the oxidization of varnish and/or various chemical reactions that take place in the paint layers. • Craquelure – a network of fine cracks or crackles on the surface of a painting, caused chiefly by shrinkage of paint film or varnish, but could also be a result of weakening of the ground and/or support. • Layers separation – Delaminations between layers of paint, between the paint and the ground, or possibly between the ground and the support. This phenomenon can be attributed to that fact that different paints have dissimilar expansion properties. Also, the ground and paint layers have different stiffness [1, 2]. The most common reason for layers separations to occur is due to changes in the material stiffness with age – the paint layers become more rigid, while the ground loses stiffness. All of these factors contribute to accumulating stresses and consequent delaminations. • Biodeterioration – regions of some paintings contain biological components; they can be source of food for insects, larvae, or even small rodents. For example, woodworm or a larvae of certain wood-boring beetles (for example Ambrosia beetles (Platypodidae, Scolytidae), Common furniture beetle (Anobium punctatum), Death watch beetle 1 9th International Conference on NDT of Art, Jerusalem Israel, 25-30 May 2008 For more papers of this publication click: www.ndt.net/search/docs.php3?MainSource=65