Appl Phys A (2009) 95: 387–399 DOI 10.1007/s00339-009-5096-3 Rapid initial dimensional changes in wooden panel paintings due to simulated climate-induced alterations monitored by digital coherent out-of-plane interferometry E. Bernikola · A. Nevin · V. Tornari Received: 16 December 2008 / Accepted: 18 December 2008 / Published online: 28 January 2009 © Springer-Verlag 2009 Abstract Climate and environmental change may provoke constant microscopic dimensional alterations to organically composed works of art. The complexity of alterations ob- structs the classification of destructive effects and sustain- able strategies for preservation, and systematic investigation of change requires safe inspection tools, repeatable proce- dures and non-perturbing approaches. In this paper, a state- of-the-art description on the dimensional monitoring tools for the assessment of the effects of climate fluctuations in paintings is given. Rapid initial start-up reactions of alter- ation processes that may simulate endangered conditions, which may be encountered during transportation of works of art, are studied. The case of wooden panel paintings is considered here as panels are representative models of in- homogeneous organic construction. The effect of the sur- face movement of panel painting surfaces due to simulated changes in temperature and relative humidity is characteris- tic of structural deterioration and as such these effects are primarily monitored in the start-up of the reaction process. The environmentally-provoked spatial alteration is recorded in full-field surface coordinates using optical coherent out- of-plane digital interferometry in a geometry utilizing holo- graphic speckle patterns. Results demonstrate the suitabil- ity of the method to follow the start-up simulated process E. Bernikola ( ) · A. Nevin · V. Tornari Institute of Electronic Structure and Laser (IESL), Foundation for Research and Technology-Hellas (FORTH), P.O. Box 1527, 71110 Heraklion, Crete, Greece e-mail: ebern@iesl.forth.gr Fax: +30-281-0391305 A. Nevin Dipartimento di Fisica, Politecnico di Milano, Piazza Leonardo da Vinci 32, 20133 Milan, Italy in real time directly from the work of art and to follow the rate of reaction towards equilibrium. The effectiveness of the full surface assessment provided in real time is presented and provides significant advantages compared to alternative techniques which are based on fragmented solutions. PACS 81.70.Fy · 87.15.-v · 89.20.-a · 42.40.Kw · 83.80.Mc 1 Introduction Paintings on wooden surfaces are extremely widespread, both historically and geographically. A major issue in the conservation of panels is the behaviour and structural move- ment of the wooden support, especially due to fluctuations in environmental conditions. In this work, digital holographic speckle interferometry has been employed in order to mon- itor surface displacement. A painting may contain a number of layers, which in- clude the substrate (wood), preparation layers, paint layers, surface treatments (varnishes) and added materials (Fig. 1). Preparation layers, applied onto a roughened surface of the wood, could consist of reflective white minerals includ- ing calcite (powdered calcium carbonate) or gypsum (hy- drated calcium sulphate) mixed with animal glue and also may include layers of canvas (Fig. 1). Paint layers consist of inorganic and organic pigments and colourants dispersed in a medium, including animal glues, eggs and milk, or oil- based binder [1, 2]. Varnishes are often applied to change the appearance of the painting and to protect the paint layer. Thus, painted wooden artworks can be considered a class of composite structures of multiple layers and panel paintings may react structurally as composite objects, with contribu- tions to their structural behaviour as a result of the combined responses from their components.