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.
We report on a method for recovering data from a simple portable Digital Speckle Pattern Interferometer intended for utilization outside of laboratory conditions, without anti-vibration devices. We used the system for monitoring the structural behavior of a painting on wood, hanging on a wall. In such a situation, fringes, produced by the object displacements, were affected by random distortions caused by environment noise. However a satisfactory number of undistorted, or barely distorted, fringe patterns were found and utilized for processing.
We performed fast continuous acquisitions of consecutive interferograms, picking usable fringe patterns out of a large amount of recorded frames. This is the crucial task in the measurement procedure. For this purpose we developed a software routine, based on jointly analysis of both spectral content and fringe image sharpne ss, as selection rule. From the selected frames, by using a simple approach based on Hilbert Transform and Phase Unwrapping, via MAx-flow (PUMA) algorithm, we were able to evaluate the painting whole structure deformations, caused by environmental thermo-hygrometric fluctuations.
Electronic Speckle Pattern Interferometry (ESPI), a non-contact and non-destructive optical techniques, was employed for assessing the conservation state of a XVI Century painting on wood (72x88x1,9 cm). By a long term analysis, the whole structure alterations, induced by the room temperature and relative humidity variations, were evaluated. Measurement of the whole painting structural bends was achieved. Local flaws and hidden detachments of pictorial layers from the support, which cannot be recognized by traditional art-restorer methods, were also revealed. This work was prevalently aimed at achieving a simple approach, in the laboratory practice, to get an intuitively user-friendly method for art conservators, not accustomed to high-tech or math based methods. The results demonstrate that ESPI can largely improve the traditional art conservation survey techniques.
Thermal Quasi Reflectography (TQR), e.g. imaging in the thermal band 3-5 μm (MWIR), is discussed as innovative tool
for the noninvasive analysis of pictorial surface layers in artworks, and its potential is demonstrated in some applications.
The results encourage further developments in this field. The novel experimental technique, which has been recently
introduced by the authors, is reviewed here giving focus to current research and potential applications.
"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.
Imaging methods offer several advantages in the field of conservation allowing to perform non-invasive inspection of
works of art. In particular, non-invasive techniques based on imaging in different infrared (IR) regions are widely used
for the investigation of paintings. Using radiation beyond the visible range, different characteristics of the inspected
artwork may be revealed according to the bandwidth acquired. In this paper we present the recent results of a joint
project among the two research institutes DIMEG and CNR-INO, and the restoration facility Opificio delle Pietre Dure,
concerning the wide-band integration of IR imaging techniques, in the spectral ranges NIR 0.8-2.5 μm, MIR 3-5 μm,
and FIR 8-12 μm, for in situ analysis of artworks. A joint, multi-mode use of reflection and thermal bands is proposed
for the diagnostics of mural paintings, and it is demonstrated to be an effective tool in inspecting the layered structure.
High resolution IR reflectography and, to a greater extent, IR imaging in the 3-5 μm band, are effectively used to
characterize the superficial layer of the fresco and to analyze the stratigraphy of different pictorial layers. IR
thermography in the 8-12 μm band is used to characterize the support deep structure. The integration of all the data
provides a multi- layered and multi-spectral representation of the fresco that yields a comprehensive analysis.
Surface topography is very important for many applications. Today the most used techniques on artworks and stone artifacts
require long acquisition times and invasive interventions. For this reason, here a non-contact device improved in portability
is described. It can acquire wide areas in short times, so it is suitable for topography reconstruction with spatial resolution
of some tens of micrometers.
The starting point is a commercial conoscopic probe, the Optimet Conoline, that is able to reconstruct the depth profile
of a surface line probed by a built-in laser. Its accuracy and acquisition speed are as high as to return wide measured areas
in short times; its resolution permits fine details reproduction. Low interference with the artwork, high portability and low
response to environmental noise are the ingredients for the instrumental setup.
In the field of art conservation non-invasive techniques based on imaging in different spectral regions are widely used for
investigation of paintings. Using radiation beyond the visible range, different characteristics of the inspected artwork
may be revealed according to the bandwidth acquired. Beyond the traditional diagnostic methods, such as reflectography,
thermography, selective multi-spectral analysis in the near-infrared region has been recently demonstrated to be a
promising tool for investigating pictorial layers. In this work we present the results of a multidisciplinary collaboration
among two research institutes and the Accademia Galleries of Venice concerning an integrated approach for multi-view
and multi-spectral imaging data analysis for the diagnostics of paintings. In order to perform this integrated analysis, a
graphical user interface with options such as image adjustment, overlaying and transparency variation was designed. The
effectiveness of this integrated approach is recognized by the operators in the field of conservation that may thus have at
their disposal the complete set of information spanning the different characteristics of the object under investigation.
Data integration provides a multi-layered and multi-spectral representation of the painting that yields a comprehensive
analysis, confirms the anomalies individuation and reduces the ambiguity of information coming from a single diagnostic
method.
We designed and built a simple fiber-optic confocal laser-scanning interference microscope, operating in the near
infrared (NIR), for the analysis of paintings. We applied this instrument to the non-invasive optical sectioning of the
paint layers. The device was tested on both laboratory samples and ancient paintings. The preliminary results show that
optical sections obtained by NIR confocal microscopy are comparable to those recorded with well known optical
coherence tomography and a few examples of application are presented.
KEYWORDS: Scanners, Infrared imaging, Near infrared, Light sources and illumination, Infrared radiation, Sensors, Principal component analysis, Transparency, Diagnostics, Head
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
paints.
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,
perfectly superimposing.
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).
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.
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.
KEYWORDS: 3D image processing, 3D modeling, Photography, Corrosion, Statistical analysis, Surface roughness, 3D metrology, Data acquisition, Image processing software, Cultural heritage
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.
In the last few years many non-destructive techniques have entered the field of painting conservation, and most of them are routinely applied to study and monitoring the painting status. Among them optical techniques are by now widely diffused and extremely well received because of their effectiveness and safety, nevertheless none of them is suitable for a quantitative characterization of varnish. One of the most important and often controversial stages of painting restoration is the surface cleaning process up to now being carried out without any tool to measure the actual varnish thickness but microscope observation of micro-detach. In this work we present an application of Optical Coherence Tomography to non-destructive diagnostics of artwork: the potentiality of this technique is demonstrated by measuring the thickness of the varnish layer in a fragment of a nineteenth-century oil painting.
KEYWORDS: Ultraviolet radiation, 3D modeling, RGB color model, Luminescence, 3D acquisition, Infrared imaging, Visible radiation, 3D image processing, 3D metrology, Sensors
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.
KEYWORDS: Data acquisition, Image registration, Stereoscopy, Three dimensional sensing, RGB color model, 3D metrology, 3D modeling, 3D acquisition, Infrared imaging, Ultraviolet radiation
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.
KEYWORDS: 3D modeling, 3D metrology, Diagnostics, Laser development, Luminescence, 3D acquisition, 3D image processing, 3D imaging standards, Laser scanners, Head
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.
KEYWORDS: 3D modeling, Laser scanners, 3D scanning, 3D metrology, 3D-TOF imaging, Data modeling, Scanners, Data acquisition, 3D acquisition, Laser development
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.
We report about a recent implementation of the INOA scanning device for infrared reflectography. The realization of a new optical head allows the simultaneous acquisition of the reflectogram and the colour image of the painting, perfectly superimposing. We show two example of application of this new device in the analysis of two ancient paintings: the Madonna con Bambino e Santi by Matteo di Giovanni and the La Tempesta by Giorgione.
KEYWORDS: 3D modeling, Laser scanners, Diagnostics, 3D metrology, 3D imaging standards, Polishing, Surface finishing, Laser development, 3D scanning, Environmental sensing
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.
KEYWORDS: 3D modeling, Diagnostics, 3D image processing, Infrared imaging, Ultraviolet radiation, Luminescence, 3D metrology, Superposition, CCD cameras, Data integration
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.
KEYWORDS: 3D modeling, Laser scanners, 3D metrology, 3D scanning, Data modeling, Data acquisition, Systems modeling, 3D-TOF imaging, Scanners, Calibration
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.
KEYWORDS: Statistical analysis, Data acquisition, 3D modeling, Diagnostics, In situ metrology, Microscopes, Computing systems, 3D scanning, 3D metrology, Optical components
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.
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.
KEYWORDS: 3D modeling, Laser scanners, CCD cameras, Cultural heritage, 3D scanning, 3D metrology, Diagnostics, 3D acquisition, Instrument modeling, 3D image processing
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).
We present a nondestructive, high resolution optical technique to obtain the surface topography of ancient paintings. The method is based on the projection of a grid of parallel lines, using white light, onto the surface to be analyzed. When viewed at an angle different from the projection angle, the grid pattern appears deformed by the surface shape. This pattern is digitized and then processed using a spatial-carrier phase-shifting algorithm that allows recovering the surface height map with high precision. The method relies on very simple equipment, gives immediate quantitative results, and is suitable for in situ measurements. It permits the recording of topographic maps of ancient paintings as well as the measurement of local detachments of the paint layer. A theoretical analysis of the method is discussed, together with a description of the data analysis algorithm. Finally, we provide some experimental results concerning the diagnostic of a twelfth-century masterpiece.
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