1. M. Bellini 1, C. Corsi 2, R. Fontana 1, M. Materazzi 1, M. Mastroianni 1, L.Pezzati 1, A.Tortora 1 1 CNR-INOA Istituto Nazionale di Ottica Applicata (Florence) 2 LENS - University of Florence M. Bellini 1, C. Corsi 2, R. Fontana 1, M. Materazzi 1, M. Mastroianni 1, L.Pezzati 1, A.Tortora 1 1 CNR-INOA Istituto Nazionale di Ottica Applicata (Florence) 2 LENS - University of Florence OCT applied to artworks: results CNR-INOA Istituto Nazionale di Ottica Applicata ADG - Artwork Diagnostic Group Optical techniques in artwork conservation Optical Coherence Tomography Optical Coherence Tomography (OCT) is a low coherence optical interferometry method providing high resolution and cross-sectional imaging of partially transparent or scattering tissue on a micrometer scale in situ and in real time. Based on broadband interferometry: depth profiling is obtained through the measurement of optical path length or phase difference between the sample and the reference arm. OCT is an efficient diagnostic imaging tool in the biomedical applications (ophthalmology, dermatology). Image resolution is one or two order above the conventional ultrasound-based methods UNDERDRAWING GROUND VARNISH PAINT LAYER PANEL 0.5÷1 mm 50÷100  m UVVISVIS IR RXRX 50÷200  m RX IR-reflectography false-colour UV fluorescence multispectral imaging 3D survey Optical techniques in Artwork: Effectiveness and safety for frail and precious objects In the last decade science has offered a fundamental contribution to conservation of paintings and the use of optical non invasive analysis is becoming widespread in the monitoring and restoration phases. So far, optical techniques have been of great support for the characterization of painting layers Reflectography Underdrawing, underpaintings Multisdpectral imaging. Spectral and colorimetric characterization of the painting surface Nevertheless none of them is suitable for a quantitative characterization of the varnish layer. Role of the varnish layer. The varnish film was generally spread on the painting both to protect it and to make it brilliant. Surface cleaning is one of the most important and sometimes controversial stages of the conservation process: decisions have to be made regarding partial or complete removal of varnish. Restorers’ and conservators’ work would be considerably helped by the monitoring of varnish removal. Raffaello’s Madonna del Cardellino: detail of the painting Restored region Opaque region Varnish thickness: old technique -> stratigraphy Varnish thickness: new technique -> optical coherence tomography A painting’s micro-sample is cut and embedded in a transparent liquid resin to form a small block. After solidification, the block is polished so to highlight the cross-section of the fragment by means of microscope examination. Drawbacks: invasive and destructive analysis localized information referred to fringe areas non-invasive and non-destructive analysis can be performed everywhere on the painting surface. Drawback: Up to now, we are not able to make a complete painting stratigraphy IVUS OCT Brezinski, et al., Am. J. Cardiology 77 (1996): delineation of arterial layers Future improvement can be very useful to achieve a better resolution and a better optical depth to detect also the painted layers under the varnish film. In a new configuration the setup should become cheap and compact enough to allow also in situ analysis. The OCT has the potential to become an alternative non invasive tool for painting stratigraphy diagnostics. How to reach us INOA National Institute for Applied Optics Largo Enrico Fermi 6, Firenze, Italy http://www.ino.it ADG Art Diagnostic Group http://arte.ino.it beniculturali@ino.it Optical Coherence Tomography (OCT) for painting diagnostics Our experimental setup lens mirror translation stage photodiode Broadband SLED source Fiber coupled  = 1550 nm   100nm  z  10nm oscilloscop e Michelson interferomete r based on a fiber coupler sample lens personal computer to translation stages translation stage Depth resolution: By adjusting the length of reference arm, it is possible to detect the signal from specific depths within the sample and thus build up a cross-sectional image. The interferograms have been obtained by acquiring a series of OCT images with a step of 5  m in the x direction. Conclusions ACKNOWLEDGMENTS We are indebted to Roberto Bellucci and Cecilia Frosinini (Opificio delle Pietre Dure) for giving us the possibility to study an ancient painting and for the microscope analysis for the successive comparison. 3mm 2mm z x step1 step2step3 Spectral reflectance factor before varnish removals Spectral reflectance factor after varnish removal Signal processing  The software performs a data smoothing and recovers the envelope of the signal for each depth scan (Z direction)  The measurement is repeated for each transversal step (X direction) We obtain the reflectivity map of the sample vs. depth and transversal position. x z Thanks to the collaboration with the Opificio delle Pietre Dure in Florence we have had the possibility to perform OCT analysis on the Ritratto Trivulzio, by Antonlello da Messina, in order to monitor the different steps of varnish layer removal during the restoration The OCT analisys was accompanied by the multispectral analysis of the artwork aimed to monitor the evolution of spectral reflectance and colorimetric coordinate of the three Region Of Interest (ROI)