The moir´e method is a well-known tool in NDT; it is based on the principle of superposition of two sets of lines or gratings, which creates a moir´e pattern that can reveal surface deformations caused by underlying defects or damage. In this paper, we propose a simple artwork diagnostic using the moir´e method and a smartphone. The technique is based on coupling the acquisition of fringe patterns by the smartphone camera to an effective fringe generator. The fringe generator consists of a diffractive optical element (DOE) illuminated by a laser diode; this optical device proved to be very effective thanks to its ability to produce in a simple way grid patterns of different spatial frequencies. The smartphone camera is used to capture the grid patterns and to store them in the cloud. We demonstrate the proposed approach by giving some preliminary experimental results.
In the engineering field, surface metrology is a valuable tool codified by international standards that enables the quantitative study of small-scale (down to micrometer) surface features, i.e., the surface topography. However, it is not recognized as a resource in heritage science. In literature we find a large use of qualitative inspection of surface morphology or of single-parameter roughness analysis, which confirms the need and potential of such diagnostics. Reasons of the gap are variegate; artworks are hand-made peculiar targets with heterogeneous surfaces, a multiscale approach is necessary, lack of guidelines and unclear meaning of surface roughness descriptors. We propose a critical-constructive discussion through Proof-of-Concept (POC) applications, on the use of surface metrology based on ISO descriptors. Exemplary case studies include: 1) In situ and in-process monitoring of painting microtexture in a Venetian masterpiece: wide and in-band roughness analysis is performed through the complementary use of amplitude, spatial, and hybrid parameters. 2) Multiscale roughness analysis for treatment monitoring in highly reflective metal artworks, requiring high micrometer accuracy in both depth (0.1 µm and lateral (5 µm) directions: surface analysis is performed on scale-limited components to discriminate different surface processes. Surface data are acquired using a prototype of a laser scanning profilometer based on conoscopic holography, with a versatile setup and a surface data pipeline tailored to artwork applications.
The surface is the most representative part of an artwork and it is also the part most exposed to alterations due to interaction with the surrounding environment. Non-destructive surface monitoring is of crucial importance in preserving and conserving cultural heritage and optical interferometric techniques allow to acquire the surface structure down to the submicrometric scale. In this work, we start from laser microprofilometry based on conoscopic holography sensors to unlock a new way of measuring the surface. In the last years, this technique has proven effective for surface diagnostic in heritage science providing high-quality surface dataset on diffusive, highly reflective, and polychrome artworks. However, an open problem in profilometry is the spatial referencing of surface topography at the micrometer scale, due to the lack of references in the height data with respect to the visually readable surface. We have recently developed a solution that exploits the raw intensity signal collected by the single-point sensor (i.e. the backscattered signal of the laser diode) and the interferometric height dataset, which are intrinsically registered. This method provides additional information about material texture, color variations or artist’s marks that enable spatial registration and data fusion tasks, otherwise difficult in traditional laser profilometry. In this paper we analyzed the feasibility and the performance of the whole process chain from the acquisition to the exploitation of the dual height-intensity datasets, focusing the attention on the raw intensity signal interpreted as a “raw reflectance signal”. We demonstrate the effectiveness of the proposed approach by presenting results on exemplary case studies.
In this paper, a method for artworks monitoring is proposed, able to perform simultaneously speckle interferometry and speckle photography, thus the system can map both out-of-plane and in-plane displacements. The aim is to keep it as simple as possible to increase its possibilities to be routinely used in restoration laboratories. Though simple, the proposed method is tailored to some specific needs of artwork diagnostics.
Infrared methods are of great importance in nondestructive testing of artworks, allowing a remote and wide-field imaging of interesting hidden features. Here we discuss a workflow based on thermal imaging in the mid infrared 3-5 micron range for the evaluation of subsurface defects in frescoes. Particular attention is payed to obtaining a high resolution (submillimetric) localization of the defects. The transfer of diagnostics techniques into real world applications, is discussed through the proof of concept of the proposed workflow on frescoes at the Sforza Castle (Milan, Italy).
Changes of temperature and relative humidity of the environment where the artefact is stored can cause deformations of the surface that can harm the object or affect the repeatability of the measurement. Currently, there are very few techniques and approaches that allow studying non-invasively the surface deformations of objects of different sizes maintaining accuracy of the order of micrometres. To address this problem, three different systems based on a conoscopic holography sensors have been tested on hygroscopic samples. Moreover, we implemented a low-cost apparatus for controlling relative humidity. Eventually, we investigated procedures that use reference standards, insensitive to thermal and hygrometric variations with the scope to assess short and long-term drifts of the instrumental set-up. We tested the approach on samples of paper and lambskin parchment and on a wooden icon.
In recent years, smartphones have developed tumultuously; in fact, they have increasingly taken on the role of portable and compact personal computers equipped with a range of sensors and applications capable of monitoring, for example, physical activity, heartbeat and sleep. Their ability to manage and transmit data makes them a very interesting tool even in the scientific field, where the concept of “lab in a phone” is gaining ground. In this work, after briefly summarizing these new approaches, we will consider the application of smartphones to the diagnostics of Cultural Heritage.
The characterization of the surface morphology and the material layers stratigraphy is a pivotal step in several stages of the conservation process of the artwork. Generally, optimal characterization of the surface cannot be achieved using a single technique but is not always possible to find techniques that can be coupled effectively. Surface maps were retrieved using acoustic microscopy and conoscopic laser holography over a set of reference samples. The surface maps compared for showing possible way to better characterize the surface morphology when their information is combined. The final data give us a more complete surface and subsurface digitalization while the results obtained are discussed highlighting the main pros and cons of the two techniques. Thus besides having insights on the effectiveness and on the performance of the processes, it is also evident that uncertainties associated with the measurement can be overcome and a single more accurate representation of the surface can be derived using both scanning methods.
Surface metrology of artworks requires the design of suitable devices for in-situ non-destructive measurement together with reliable procedures for an effective analysis of such non-engineered variegate objects. To advance the state-of-the-art it has been implemented a versatile optical micro-profilometry taking advantage of the adapt- ability of conoscopic holography sensors, able to operate with irregular shapes and composite materials (diffusive, specular, and polychrome) of artworks. The scanning technique is used to obtain wide field and high spatially resolved areal profilometry. The prototype has a modular scheme based on a set of conoscopic sensors, extending the typical design based on a scanning stage and a single probe with a limited bandwidth, thus allowing the collection of heights data from surface with different scales and materials with variegate optical response. The system was optimized by characterizing the quality of the measurement with the probes triggered in continuous scanning modality. The results obtained on examples of cultural heritage objects (2D paintings, 3D height-relief) and materials (pictorial, metallic) demonstrate the versatility of the implemented device.
In this paper we analyze some problems related to the acquisition of multiple illumination images for Polynomial Texture Maps (PTM) or generic Reflectance Transform Imaging (RTI). We show that intensity and directionality nonuniformity can be a relevant issue when acquiring manual sets of images with the standard highlight-based setup both using a flash lamp and a LED light. To maintain a cheap and flexible acquisition setup that can be used on field and by non-experienced users we propose to use a dynamic calibration and correction of the lights based on multiple intensity and direction estimation around the imaged object during the acquisition.
Preliminary tests on the results obtained have been performed by acquiring a specifically designed 3D printed pattern in order to see the accuracy of the acquisition obtained both for spatial discrimination of small structures and normal estimation, and on samples of different types of paper in order to evaluate material discrimination.
We plan to design and build from our analysis and from the tools developed and under development a set of novel procedures and guidelines that can be used to turn the cheap and common RTI acquisition setup from a simple way to enrich object visualization into a powerful method for extracting quantitative characterization both of surface geometry and of reflective properties of different materials. These results could have relevant applications in the Cultural Heritage domain, in order to recognize different materials used in paintings or investigate the ageing status of artifacts’ surface.
Cultural Heritage is discovering how precious is thermal analysis as a tool to improve the restoration, thanks to its ability to inspect hidden details. In this work a novel dual mode imaging approach, based on the integration of thermography and thermal quasi-reflectography (TQR) in the mid-IR is demonstrated for an effective mapping of surface materials and of sub-surface detachments in mural painting. The tool was validated through a unique application: the “Monocromo” by Leonardo da Vinci in Italy. The dual mode acquisition provided two spatially aligned dataset: the TQR image and the thermal sequence. Main steps of the workflow included: 1) TQR analysis to map surface features and 2) to estimate the emissivity; 3) projection of the TQR frame on reference orthophoto and TQR mosaicking; 4) thermography analysis to map detachments; 5) use TQR to solve spatial referencing and mosaicking for the thermal-processed frames. Referencing of thermal images in the visible is a difficult aspect of the thermography technique that the dual mode approach allows to solve in effective way. We finally obtained the TQR and the thermal maps spatially referenced to the mural painting, thus providing the restorer a valuable tool for the restoration of the detachments.
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.
3D optical techniques are proven to be useful for the study of the artwork's surface morphology because they allow noncontact
and noninvasive measurements. Detailed topographic analysis of the surface including a quantitative evaluation
of defects related to the painting layers can be performed by means of holographic conoscopy on a micron scale.
Moreover, artwork surfaces can be examined with suitable 2D optical techniques in the IR range to investigate defects at
a subsurface level. In particular, thermography in the Mid-IR band 3-5 micron allows the detection and spatial mapping
at a suitable resolution of the delamination of painted layers. An integrated model of the surface-subsurface defect
distribution can be obtained by superimposing the results of the two above techniques, for a more effective analysis and
monitoring of the delamination decay typology according to the specific case study. The delamination of organic paint
layers from inorganic support is a decay that affects many wall paintings based on both traditional (oil and tempera) and
synthetic media (acrylic and vinyl copolymers). Defining the factors that cause delamination, finding out strategies to
restore the adhesion between paint layers and support, and monitoring the restoration intervention are fundamental
conservation objectives. This paper investigates the feasibility of a joint use of holographic conoscopy and IR
thermography for exploring the delamination decay typology of ad hoc laboratory samples. Set up includes a scanning
micro-profilometer, and a thermal PtSi camera with a controlled IR source to provide heating stimulation.
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.
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: 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.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.