MA-XRF and OCT techniques as tools for identification of past renovation attempts as well as aid in current restoration treatment of the painting ‘Christ before Caiaphas’
Abstracts
The aim of this work is to present an integrated approach based on various types of analyses of an oil-on-canvas painting to investigate layers of overpaint and varnishes added throughout the centuries. The project focused on an extremely overpainted altar-painting ‘Christ before Caiaphas’. MA-XRF and OCT were employed as diagnostic techniques.
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Purpose
1The aim of this work is to present an integrated approach based on various types of analyses of an oil-on-canvas painting to investigate layers of overpaint and varnishes added throughout the centuries. Simultaneously to the non-destructive research methods, samples were taken and investigated micro-chemically.
The Painting
2This project was conducted as a part of conservation-restoration diploma project focusing on an extremely overpainted altar-painting ‘Christ before Caiaphas’, painted in oil on canvas (late 18th century, Calvary of Pakość, Poland, size 148 x 96 cm). Due to previous improper restoration treatments of the painting some examination methods, like the UV-excited fluorescence of the surface of the paint surface, were difficult to interpret.
Methods
3Macro X-Ray Fluorescence scanning (MA-XRF) is an imaging technique which enables extended surface scans over thousands of square centimetres during a single examination. For this study the M6 JetStream scanning system from Bruker Nano GmbH was employed. It permits large surface scans – up to 70 cm x 55 cm with lateral resolution up to 50 µm. It comprises an X-ray source working at 50 kV/600 µA conditions with Rh anode and polycapillary optics. An open-air system permits imaging elements of atomic numbers not lower than 16 (sulphur).
4Optical Coherence Tomography (OCT) (ill. 1) is an interferometric non-contact and non-invasive technique of depth-resolved imaging (to obtain cross-sectional images) within media that scatter and/or absorb near-infrared light moderately. For examination a high resolution (2 µm axial, 12 µm lateral) spectral domain OCT instrument was used. A beam of near-infrared (770-970 nm) radiation of 0.8 mW was directed towards the object’s surface.
Fig.1 OCT tomograms

OCT tomograms give information about the sequence, thickness and condition of semi-transparent sub-surface layers such as varnishes and some overpaints. Additionally, OCT was employed to control the process of removing the layers of overpaints as well as thinning/removal of the varnish. (a) Tomogram collected before cleaning and removal of overpaints and varnish; (b) the result of the cleaning treatment.
Credits: Anna Faron, Magdalena Iwanicka
Fig. 2 Results of MA-XRF analysis

Caption: Assembled scans show distribution of some chemical elements. The resulting maps contain three separate scans put together in a graphic software.
Credits: Anna Faron, Magdalena Iwanicka
Conclusions
5Data acquired with MA-XRF (Fig. 2) revealed the distribution of different elements and therefore enabled not only identification of pigments, but also differentiation between primary and secondary layers which was essential for planning the conservation-restoration project with the best possible knowledge.
6With the precision enabling separation of almost every brushstroke, the subsequent phases of overpainting could be differentiated. Moreover, the MA-XRF analysis enabled assessment of the condition as well as composition of the original layers even before removing of the overpaint layers. It also allowed dating of some of the interventions, deduced from the materials that were detected.
List of illustrations
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Title | Fig.1 OCT tomograms |
Caption | OCT tomograms give information about the sequence, thickness and condition of semi-transparent sub-surface layers such as varnishes and some overpaints. Additionally, OCT was employed to control the process of removing the layers of overpaints as well as thinning/removal of the varnish. (a) Tomogram collected before cleaning and removal of overpaints and varnish; (b) the result of the cleaning treatment. |
Credits | Credits: Anna Faron, Magdalena Iwanicka |
URL | http://journals.openedition.org/ceroart/docannexe/image/5080/img-1.jpg |
File | image/jpeg, 524k |
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Title | Fig. 2 Results of MA-XRF analysis |
Caption | Caption: Assembled scans show distribution of some chemical elements. The resulting maps contain three separate scans put together in a graphic software. |
Credits | Credits: Anna Faron, Magdalena Iwanicka |
URL | http://journals.openedition.org/ceroart/docannexe/image/5080/img-2.jpg |
File | image/jpeg, 995k |
References
Electronic reference
Anna Faron, “MA-XRF and OCT techniques as tools for identification of past renovation attempts as well as aid in current restoration treatment of the painting ‘Christ before Caiaphas’”, CeROArt [Online], HS | 2017, Online since 30 May 2017, connection on 29 March 2023. URL: http://journals.openedition.org/ceroart/5080; DOI: https://doi.org/10.4000/ceroart.5080
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