Scientific Results

Determination of thickness of thin turbid painted over-layers using micro-scale spatially offset Raman spectroscopy

Year: 2016

Authors: Conti C., Realini M., Colombo C., Botteon A., Bertasa M., Striova J., Barucci M., Matousek P.

Autors Affiliation: Istituto per la Conservazione E la Valorizzazione Dei Beni Culturali (ICVBC), Consiglio Nazionale delle Ricerche, Via Cozzi 53, Milan, 20125, Italy; Istituto Nazionale di Ottica and LENS, Consiglio Nazionale delle Ricerche (CNR), Università di Firenze, Via Nello Carrara 1, Sesto Fiorentino, 50019, Italy; Research Complex at Harwell, Central Laser Facility, STFC Rutherford Appleton Laboratory, Harwell, Oxford, OX11 0QX, United Kingdom

Abstract: We present a method for estimating the thickness of thin turbid layers using defocusing micro-spatially offset Raman spectroscopy (micro-SORS). The approach, applicable to highly turbid systems, enables one to predict depths in excess of those accessible with conventional Raman microscopy. The technique can be used, for example, to establish the paint layer thickness on cultural heritage objects, such as panel canvases, mural paintings, painted statues and decorated objects. Other applications include analysis in polymer, biological and biomedical disciplines, catalytic and forensics sciences where highly turbid overlayers are often present and where invasive probing may not be possible or is undesirable. The method comprises two stages: (i) a calibration step for training the method on a well characterized sample set with a known thickness, and (ii) a prediction step where the prediction of layer thickness is carried out non-invasively on samples of unknown thickness of the same chemical and physical make up as the calibration set. An illustrative example of a practical deployment of this method is the analysis of larger areas of paintings. In this case, first, a calibration would be performed on a fragment of painting of a known thickness (e.g. derived from cross-sectional analysis) and subsequently the analysis of thickness across larger areas of painting could then be carried out non-invasively. The performance of the method is compared with that of the more established optical coherence tomography (OCT) technique on identical sample set.

Journal/Review: PHILOSOPHICAL TRANSACTIONS OF THE ROYAL SOCIETY SERIES A-MATHEMATICAL PHYSICAL AND ENGINEERING SCIENCES

Volume: 374 (2082)      Pages from: 20160049  to: 20160049

More Information: J.S. is supported by IPERION CH project GA 654028, funded by EU community\’s H2020-research infrastructure programme.
KeyWords: Calibration; Chemical analysis; Forecasting; Functional polymers; Optical tomography; Raman spectroscopy; Tomography, Cross sectional analysis; Cultural heritage objects; Cultural heritages; Non-invasive; Paint layer thickness; Raman microscopy; Spatially offset raman spectroscopies; Thickness, Spectrum analysis
DOI: 10.1098/rsta.2016.0049

Citations: 7
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English