27 July 2011 Optical techniques for the characterization of surface-subsurface defects in painted layers
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3D optical techniques are proven to be useful for the study of the artwork's surface morphology because they allow noncontact and noninvasive measurements. Detailed topographic analysis of the surface including a quantitative evaluation of defects related to the painting layers can be performed by means of holographic conoscopy on a micron scale. Moreover, artwork surfaces can be examined with suitable 2D optical techniques in the IR range to investigate defects at a subsurface level. In particular, thermography in the Mid-IR band 3-5 micron allows the detection and spatial mapping at a suitable resolution of the delamination of painted layers. An integrated model of the surface-subsurface defect distribution can be obtained by superimposing the results of the two above techniques, for a more effective analysis and monitoring of the delamination decay typology according to the specific case study. The delamination of organic paint layers from inorganic support is a decay that affects many wall paintings based on both traditional (oil and tempera) and synthetic media (acrylic and vinyl copolymers). Defining the factors that cause delamination, finding out strategies to restore the adhesion between paint layers and support, and monitoring the restoration intervention are fundamental conservation objectives. This paper investigates the feasibility of a joint use of holographic conoscopy and IR thermography for exploring the delamination decay typology of ad hoc laboratory samples. Set up includes a scanning micro-profilometer, and a thermal PtSi camera with a controlled IR source to provide heating stimulation.
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C. Daffara, C. Daffara, R. Fontana, R. Fontana, M. Melchiorre Di Crescenzo, M. Melchiorre Di Crescenzo, S. Scrascia, S. Scrascia, E. Zendri, E. Zendri, "Optical techniques for the characterization of surface-subsurface defects in painted layers", Proc. SPIE 8084, O3A: Optics for Arts, Architecture, and Archaeology III, 80840X (27 July 2011); doi: 10.1117/12.889959; https://doi.org/10.1117/12.889959

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