In this paper we present a scanning device for multispectral imaging of paintings in the 380-800 nm spectral region; the
system is based on a spectrophotometer for contact-less single-point measurements of the spectral reflectance with 10
nm resolution. Two orthogonal XY translation stages allow to scan up to 1,5 m2 with spatial resolution up to 8 dots/mm.
As an application we present the results of the measurements carried out on Ritratto Trivulzio by Antonello da Messina
and Madonna in gloria tra Santi by Andrea Mantegna. Besides spectra comparison also multivariate image analyses
(MIA) have been performed by considering the multi-spectral images as three-way data set.
In order to point out the slight spectral differences of two areas of a painting we analyzed its multispectral data cube by
means of the Principal Component Analysis (PCA) and the K-Nearest-Neighbouring Cluster Analysis (KNN).
A variety of scientific investigation methods applied to paintings are, by now, an integral part of the repair process, both
to plan the restoration intervention and to monitor its various phases. Optical techniques are widely diffused and
extremely well received in the field of painting diagnostics because of their effectiveness and safety. Among them
infrared reflectography is traditionally employed in non-destructive diagnostics of ancient paintings to reveal features
underlying the pictorial layer thanks to transparency characteristics to NIR radiation of the materials composing the
High-resolution reflectography was introduced in the 90s at the Istituto Nazionale di Ottica Applicata, where a prototype
of an innovative scanner was developed, working in the 900-1700 nm spectral range. This technique was recently
improved with the introduction of an optical head, able to acquire simultaneously the reflectogram and the color image,
In this work we present a scanning device for multi-spectral IR reflectography, based on contact-less and single-point
measurement of the reflectance of painted surfaces. The back-scattered radiation is focused on square-shaped fiber
bundle that carries the light to an array of 14 photodiodes equipped with pass-band filters so to cover the NIR spectral
range from 800 to 2500 nm
One of the most important and sometimes controversial stages of the conservation process is surface cleaning:
decisions have to be made regarding partial or complete removal of varnish. Technical considerations include
selection of a method that allows a great deal of control in the cleaning process, so that undesired layers can be
removed without damage to the underlying ones. Traditional cleaning methods include mechanical or chemical
removal, and restorers and conservators work would be considerably helped by the knowledge of the varnish
thickness. Up to now thickness measurement has been performed in an invasive way by means of stratigraphy, a well
known painting structure investigation technique since half a century. In this work we present an application of
Optical Coherence Tomography (OCT), a well-established technique for biomedical applications, for non-destructive
measuring of the varnish film thickness during the cleaning process of an ancient painting, the Ritratto Trivulzio by
Antonello da Messina. OCT images of three differently cleaned areas on the painting surface were acquired and the
results were compared with a spectral characterization of the same areas.
We present a scanning device for 32-band multi-spectral imaging of paintings in the 380÷800 nm spectral region. The system is based on contact-less and single-point measurement of the spectral reflectance factor. Multi-spectral images are obtained by scanning the painted surface under investigation. An adjustment procedure was established and calibration was performed by means of a set of seven matt ceramic color tiles certified by National Physical Laboratory (UK). Colorimetric calculations were carried out in the XYZ colorimetric space, by following the CIE recommendations and choosing the D65 standard illuminant and the 1931 standard observer. Measurement campaigns were carried out on several paintings in situ and at the INOA Optical Metrology Laboratory located inside the Opificio delle Pietre Dure in Florence. As an example we report herein on the measurements carried out on the Madonna in gloria tra Santi by Andrea Mantegna, (at present in the Pinacoteque of the Castello Sforzesco in Milan). Multivariate image analyses (MIA) were performed by considering the multi-spectral images as three-way data set. The stack of detected images were unfolded in a 2D data matrix and analyzed by the conventional Principal Component Analysis (PCA).
A quantitative morphological analysis of archaeological objects represents an important element for historical evaluations, artistic studies and conservation projects.
At present, a variety of contact instruments for high-resolution surface survey is available on the market, but because of their invasivity they are not well received in the field of artwork conservation. On the contrary, optical testing techniques have seen a successful growth in last few years due to their effectiveness and safety.
In this work we present a few examples of application of high-resolution 3D techniques for the survey of archaeological objects.
Measurements were carried out by means of an optical micro-profilometer composed of a commercial conoprobe mounted on a scanning device that allows a maximum sampled area of 280×280 mm2.
Measurements as well as roughness calculations were carried out on selected areas, representative of the differently degraded surface, of an ellenestic bronze statue to document the surface corrosion before restoration intervention started. Two highly-corroded ancient coins and a limestone column were surveyed to enhance the relief of inscriptions and drawings for dating purposes.
High-resolution 3D survey, beyond the faithful representation of objects, makes it possible to display the surface in an image format that can be processed by means of image processing software. The application of digital filters as well as rendering techniques easies the readability of the smallest details.
Non-destructive optical testing techniques are widely used in the field of painting diagnostics because of their effectiveness and safety. At present, many techniques for non-destructive investigations of paintings are available. Optical Coherence Tomography (OCT) is a non invasive technique allowing cross sectional imaging of partially transparent or scattering tissue which is now well-established for biomedical applications. Particularly, the OCT techniques allow evaluating multilayer tissues. Being applied to painting diagnostics, the OCT gives a possibility to measure the actual varnish thickness that is very important in painting restoration by the cleaning process. Because of complicated local structure of layers and light scattering, noise-immune signal processing methods should be used. In the paper, the Kalman filtering method involving random fringe model applied to the OCT signals is investigated and compared with conventional fringe amplitude demodulation method. Experimental results obtained when recovering OCT tomograms of paintings are presented and discussed.
In the last few years multispectral imaging has entered the field of painting diagnostics and conservation because of its effectiveness and safety. It provides spectral and colorimetric characterization of the whole paint layer, suitable to document the conservation state of the artwork and useful in the study for the identification of pigments.
Here we present a high-resolution scanning system for 32-band multispectral imaging of paintings in the 380÷800 nm spectral region. This system is based on a fast spectrometer for contact-less single-point measures mounted on two orthogonal XY translation stages. It can scan an area of 1 m2 with a spatial resolution of 4 dots/mm and a spectral resolution of 10 nm.
Spectral reflection factor and tristimulus value measurements were carried out on coloured ceramic tiles and the results were compared with the corresponding certified values.
Multispectral analysis was performed on a few ancient paintings and spectrophotometric results are shown.