Near-Infrared (NIR) reflectography is a well-established technique for painting diagnostics, offering a fundamental contribution to the conservation of paintings. Since the '80s it has been routinely applied to study the execution technique of the author, as well as the presence of pentimenti, retouches, integrations or underdrawing. In the last decades IR reflectography has been extended to the visible (VIS) spectral range, providing information about the pigment composition. Up to now the multispectral analysis is still applied at an experimental level, as the processing of the image set is not straightforward.
Rarely multispectral VIS-IR application has been applied to frescos, probably due to the lack, in most cases, of a scattering background.
In this work we present the results provided by a multispectral scanning device based on single sensor acquisition, working in the 380-2500 nm spectral range, that is a laboratory prototype specifically built for research-grade imaging. The technique have been applied on a mock up simulating a mural painting substrate where an underdrawing, made of either carbon or iron-gall ink, was covered by different surface layers of limewash, the so-called scialbo.
"Cleaning" is a process of carefully identifying the cause of any deterioration or discolouration and then removing or treating these layers. The skill of the restorer is not only to understand the techniques and media used by the artist, but also to recognize what beauty lies beneath the veils of many years of neglect or adverse conditions. Surface cleaning is then one of the most important and sometimes controversial stages of the conservation process: it is an irreversible process that generally results in substantial physical changes of the object surface, raising thus a series of questions regarding aesthetics, the potential loss of historical information, and the ability to control the cleaning process adequately. 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 damaging the underlying ones by means of traditional cleaning methods, including mechanical or chemical removal. In this work we present a study of the optical properties of painting surfaces for the characterization of the cleaning process. Analyses were carried out by means of laser micro-profilometry and confocal microscopy. Measurements were carried out on a few paintings which are under repair at the Opificio delle Pietre Dure in Florence. Selected areas were surveyed with the two above mentioned techniques and results were correlated.
A variety of optical 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. Among them infrared reflectography in wide-band
modality is traditionally employed in non-invasive diagnostics of ancient paintings to reveal features underlying the
pictorial layer thanks to transparency characteristics to NIR radiation of most of the materials composing the paints.
This technique was improved with the introduction of the multi-spectral modality that consists in acquiring the radiation
back scattered from the painting into narrow spectral bands. The technology, widely used in remote sensing applications
such as satellite or radar imaging, has only recently gained importance in the field of artwork conservation thanks to the
varied reflectance and transmittance of pigments over this spectral region.
In this work we present a scanning device for multi-NIR spectral imaging of paintings, based on contact-less and singlepoint
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 16 photodiodes equipped with pass-band filters so to cover the NIR spectral
range from 900 to 2500 nm. In particular, we describe the last instrument upgrade that consists in the addition of an
autofocus system that keeps the optical head perfectly focused during the scanning. The output of the autofocus system
can be used as a raw map of the painting shape.
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
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).
The quantitative morphological analysis of a painting surface allows to evidence form defects and to study, thus, their
influence on the stability of the paint and preparatory layers, as well as of the support. Therefore a three-dimensional
survey can be very useful in planning the restoration intervention of a painting.
In this work we present the results of the surface analysis carried out on the painting "Ultima Cena" by Giorgio Vasari.
This panel painting is severely affected by paint film wrinkling produced as a consequence of the flood that occurred in
Florence in 1966. Our analysis, accomplished to quantify the lengthening of the paint layer with respect to the one of the
support in order to plan the restoration intervention, was performed on 25 profiles separated each by 10 cm in order to
cover the whole painting surface.
A data analysis, based on morphological filtering named "Rolling Ball" transformation, was used to evaluate the length
difference between the paint layer and the panel support along each profile.
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.
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.
3D measurement and modelling have been traditionally applied to statues, buildings, archeological sites or similar large structures, but rarely to paintings. Recently, however, 3D measurements have been performed successfully also on easel paintings, allowing to detect and document the painting's surface. We used 3D models to integrate the results of various 2D imaging techniques on a common reference frame. These applications show how the 3D shape information, complemented with 2D colour maps as well as with other types of sensory data, provide the most interesting information.
The 3D data acquisition was carried out by means of two devices: a high-resolution laser micro-profilometer, composed of a commercial distance meter mounted on a scanning device, and a laser-line scanner. The 2D data acquisitions were carried out using a scanning device for simultaneous RGB colour imaging and IR reflectography, and a UV fluorescence multispectral image acquisition system. We present here the results of the techniques described, applied to the analysis of an important painting of the Italian Reinassance: `Madonna dei Fusi', attributed to Leonardo da Vinci.
We describe the application of 2D and 3D data acquisition and mutual registration to the conservation of paintings. RGB color image acquisition, IR and UV fluorescence imaging, together with the more recent hyperspectral imaging (32 bands) are among the most useful techniques in this field. They generally are meant to provide information on the painting materials, on the employed techniques and on the object state of conservation. However, only when the various images are perfectly registered on each other and on the 3D model, no ambiguity is possible and safe conclusions may be drawn. We present the integration of 2D and 3D measurements carried out on two different paintings: "Madonna of the Yarnwinder" by Leonardo da Vinci, and "Portrait of Lionello d'Este", by Pisanello, both painted in the XV century.
The aim of this work is to show how 3D techniques can be used to integrate standard diagnostic ones, adding useful and powerful tools for the restorers. A 3D model allows both to monitor restoration processes and to keep trace of any significant modification of an artwork. We present 3D measurements carried out on different kind of samples: a statue, a painting, a xylography board and two ancient coins. These surveys were carried out by means of a high-resolution laser micro-profilometer developed by the Art Diagnostic Group of the National Institute of Applied Optics. It is composed of a commercial distance meter mounted on a scanning device and allows dense data sampling with high quota resolution and accuracy.
This work is intended to show the results of a few architectural and archaeological surveys realized by means of a 3D scanning device, based on TOF (Time-Of-Flight) technology. The instrument was set up by the Art Diagnostic Group of the National Institute for Applied Optics (INOA) and it is composed by a high precision scanning system equipped with a commercial low-cost distance-meter. This device was projected in order to provide the following characteristics: reliability, good accuracy and compatibility with other systems and it is devoted to applications in Cultural Heritage field.
The aim of this work is to show how 3D techniques can be used to integrate standard diagnostics, adding useful and powerful tools for the restorers. Our plan is to assemble a few complete 3D digital models of a bronze statue, the Minerva of Arezzo, either before or during its repair, to keep trace of every significant modification occurring in the restoration process. Variations of the statue's shape, due to the removal of plaster and to the polishing of the corroded bronze surface, are indeed foreseen. 3D measurements have been realized by means of a very high-resolution laser scanner developed at INOA; the instrument is supported by a manageable software for data handling.
The measurement of the shape of an artwork usually requires a high-resolution instrumentation, in order to catch small details such as chisel marks, sculptural relieves, surface cracks, etc. 3D scanning techniques, together with new modeling software tools, allow a high fidelity reproduction of an artwork: these can be applied either to support and document its repair or for the realization of 3D archives and virtual museums. Starting from a high-resolution digital model of an object, a further step could be its reproduction by means of fast-prototyping techniques like stereo-lithography or electro-erosion. This work is aimed at showing the performance of a high-resolution laser scanner devoted to Cultural Heritage applications. The device is portable and very versatile, in order to allow in situ applications, accurate and reliable, so to capture intricate details. This laser profilometer has been used in a few surveys, the most significant of which are the monitoring the various phases of the restoration process of an ellenistic bronze (the Minerva of Arezzo, Florence), the cataloguing of some archaeological findings (from the Grotta della Poesia, Lecce) and the documenting of wooden panels surface conditions (the “Madonna del Cardellino” by Raffaello and “La Tebaide” by Beato Angelico).
Imaging techniques are widely used for the diagnostics of paintings. The results, collected by applying various imaging techniques are generally compared by the art historian who studies the object. These 2D data can be effectively integrated to form a multi-dimensional dataset, and added to a 3D digital model of the painting, thus creating a complete package of information about the opera. In this work we present some examples of applications of data integration with measurements performed on some important panel paintings. The imaging analysis was carried out by applying techniques such as infrared reflectography, colour and false colour imaging and ultraviolet fluorescence. The IR reflectogram, the false colour and the colour image are simultaneously acquired with a scanning device characterized by a high resolution (16 dots/mm2), a high tonal dynamic and point-to-point correspondence between these three images. A multi-spectral device, based on a high-resolution CCD camera, is used for UV fluorescence. The 3D relief was obtained by means of scanning micro-profilometry with a quota resolution of about 1 micron. The integration of the 3D model with the results given by several imaging techniques greatly increases the information and it eases the analysis of the painting under investigation.
The realization of an accurate 3D model of a building, a piece of architecture or a terrain has been a prerogative of the photogrammetric systems for a long time. However, recent developments in opto-electronic technology and 3D analysis software made the production of 3D models by laser scanning a practical proposition. The main advantages of laser scanners are accuracy and speed, allowing, thus, the collecting of data on a dense sampling of the object. For many architectural and industrial applications it is important to integrate the data acquired with different instruments, but a problem met with many commercial systems is the lack of compatibility with classic survey methodologies. Moreover, superimposition of results from different techniques is possible only if the output is metrically correct. This work is aimed at showing the results of some architectural and archaeological surveys realized by means of a 3D scanning device, based on the Time-Of-Flight (TOF) technology. The instrument, devoted to architectural applications in the Cultural Heritage field, was set up in order to provide the characteristics of reliability and compatibility to other systems. Such a device is composed by a high precision scanning system equipped with a commercial low-cost distance-meter.
Infrared reflectography is a prominent optical technique for non-destructive diagnostics of paintings, which allows the visualisation of details hidden by the paint layers, because of their transparency characteristics to IR radiation. High-resolution reflectography was introduced around the end of the 80s by the Istituto Nazionale di Ottica Applicata, where a prototype of an innovative scanner device was developed. This technique was recently improved with the introduction of a new optical head, able to acquire simultaneously the reflectogram and the colour image, perfectly superimposing. The technical characteristics of the IR-colour scanner guarantee: a high spatial resolution (16 points/mm2), a high tonal dynamics (thousands of grey levels), a uniform lighting of the scanned area and the punctual superimposition of the colour and IR images. Moreover we can print distortion-free reflectograms, false-colour and colour images of paintings on a 1:1 scale. The quality of the acquired reflectogram is presently higher than that obtainable with any traditional detection system, like CCD or Vidicon cameras. The point-by-point comparison between the reflectogram and the colour image of the painting, along with digital processing of the recorded images, open new possibilities for the analysis of the reflectogram. Some examples of application to the study of ancient paintings are shown.
The knowledge of the shape of an artwork is an important element for its study and conservation. When dealing with a statue, roughness measurement is a very useful contribution to document its surface conditions, to assess either changes due to restoration intervention or surface decays due to wearing agents, and to monitor its time-evolution in terms of shape variations. In this work we present the preliminary results of the statistical analysis carried out on acquired data relative to six areas of the Michelangelo’s David marble statue, representative of differently degraded surfaces. Determination of the roughness and its relative characteristic wavelength is shown.