Surface Of Artwork Research Articles

Tag recognition: A new methodology for the structural monitoring of cultural heritage

In this paper, a new methodology for measuring the cracking in the field of Structural Health Monitoring (SHM) of cultural heritage, is presented. The minimum invasiveness of this methodology permits to preserve the aesthetic appearance, a fundamental requirement in monitoring of cultural heritage. The core of the acquisition system is composed by two small adhesive tags to be attached on the artwork surface, and a high-resolution camera acquiring images of the tags. The relative distance between the optical tags for determining is determined using advanced least-squares fitting of quadratic curves and surfaces algorithms for the objective function. Here, the bi-dimensional Gaussian as objective function has been taken into account, in order to find the best configuration for determining the fitting parameters, useful for the SHM. We ran a simulation for tuning fitting algorithm parameters. Then we validated the methodology through an experimental session.

Atmospheric Monatomic Oxygen System For Non-Contact Nanoscale Cleaning Of Vandalized 20th - 21st Century Modern And Contemporary Artworks

Introduction The paper discusses defacement materials used in diverse acts of vandalism against the modern and contemporary art and stresses the need for a safe and effective methodology to treat sensitive and fragile unprotected surfaces of 20th and 21st century artworks that frequently are vandalized using carbon based materials. The paper proposes the proven concept for a nanoscale cleaning mechanism based on monoatomic oxygen, which does not require any physical contact with the surfa...

Enhanced RTI for gloss reproduction

The Digital Humanities Lab (DHLab) is a technological oriented research group within the faculty of Humanities of the University of Basel. The research profile of the DHLab integrates computer science, digital imaging, computational photography, the accessibility of digital objects and solutions for digital preservation with the aim to support scholars in the emerging field of humanities research. The project Digital Materiality, a collaboration with the Seminar of Art History, examines how new imaging and visualization methods can be applied to describe the reflection of light on surfaces of artworks. Of main interest are mosaics and early prints; both types of artworks have a strong interaction with light that can not captured adequately by standard photographic approaches. Conventional photographic processes are not able to capture the dynamic component of the light-surface interdependence that is specific for this kind of art. The technical part of the project focuses on improving the methodology that is in general described as Reflectance Transformation Imaging (RTI) techniques. RTI is an approach based on a mathematical model, that is fitted in image data derived from photographs. By modifying the mathematical model that is used to represent the light-surface interaction, the digital reproduction can be improved so that relevant attributes of artworks can be transported into the digital domain in such a way that the requirements and needs of humanities researchers to a digital representation can be fulfilled. The improvements take into account more sophisticated but still robust and simple reflection models for the realistic visualization of localized diffuse and specular surfaces within the same digital reproduction. For humanities research the most important aspect is the compatibility to web-based Virtual Research Environments (VRE). The presented approach can be integrated in such environments because the client-side visualization is implemented in WebGL. For flexibility, performance and data permanence aspects the server side will be an enhanced image server layer following the International Image Interoperability Framework (IIIF) image based environment.

Optical devices provide unprecedented insights into the laser cleaning of calcium oxalate layers

Calcium oxalates are insoluble colorless or whitish salts constituting noble patina, on both natural and artificial stone artworks' surfaces, the presence of which is extremely valued. The oxalates are not considered detrimental to the substrate, however, being often accompanied by other substances such as gypsum, silicates, and pigmented particles. They may form very adherent, relatively thick and colored layers creating disfiguring effects and hindering legibility of the pictorial surface. For this reason it may be appropriate to diminish their thickness, but patina's partial preservation is particularly required calling for extremely gradual and controllable cleaning approach. Thinning of calcium oxalate patina from a detached 16th century fresco (from Sansepolcro) was performed through the use of laser (Nd:YAG and Er:YAG) systems and chemical means (Carbogel loaded 5wt.% of tetrasodium EDTA). Optical coherence tomography (OCT), providing a non-invasive stratigraphic cross-section of the examined surface, allowed to distinguish the oxalate from the underlying original layers and therefore to have an overview about its distribution, to numerically evaluate patina's thickness range and to provide the information on the amount of the material both removed and left on the artwork's surface. Laser scanning conoscopic microprofilometry allowed for a high-density sampling of the artwork's surface providing a three-dimensional model of the surface pattern. The obtained 3D models were used to estimate the amount of material removed and to compare them with those provided by OCT. The successful exploitation of the proposed exceptional cleaning monitoring methodology may be seen as an innovative and valid support for the restorers in the conservation of mural painting or other surfaces covered by oxalate layers and may pilot more targeted, cautious and respectful cleaning intervention.

Gelling process for sodium alginate: New technical approach by using calcium rich micro-spheres

Alginate based materials have become an important class of products in many fields from the pharmaceutical industry to tissue engineering, because of their ability to create stimuli responsive hydrogels. We present a new technical approach for obtaining a controlled gelling process, based on the quantities of Ca2+ rich alginate micro-beads added as crosslinkers. The gels have been evaluated in light of the amount of Ca2+ added to the alginate solution, and in light of the different dimensions of the micro-beads, using rheological measurements to assess the variation in the storage modulus (G′), loss modulus (G′′) and complex viscosity (η*) as well as swelling and deswelling tests. The methodology was developed to obtain a material with specific characteristics for application in the field of conservation. The material had to be able to create a stable gel after being applied on the artwork surface and to confine the solvent action at the interface during cleaning operations.

Automatic registration and mosaicking of technical images of Old Master paintings

The registration of technical art conservation images of Old Master paintings presents unique challenges. Specifically, X-radiographs and reflective infrared (1000–2500 nm) images reveal shifted, or new, compositional elements not visible on the surface of artworks. Here, we describe a new multimodal registration and mosaicking algorithm that is capable of providing accurate alignment of a variety of types of images, such as the registration of multispectral reflective infrared images, X-radiographs, hyperspectral image cubes, and X-ray fluorescence image cubes to reference color images taken at high spatial sampling (300–500 pixels per inch), even when content differences are present, and a validation study has been performed to quantify the algorithm’s accuracy. Key to the algorithm’s success is the use of subsets of wavelet images to select control points and a novel method for filtering candidate control-point pairs. The algorithm has been used to register more than 100 paintings at the National Gallery of Art, D.C. and The Art Institute of Chicago. Many of the resulting registered datasets have been published in online catalogues, providing scholars additional information to further their understanding of the paintings and the working methods of the artists who painted them.

Influence of composition and roughness on the pigment mapping of paintings using mid-infrared fiberoptics reflectance spectroscopy (mid-IR FORS) and multivariate calibration.

Mid-infrared fiberoptics reflectance spectroscopy (mid-IR FORS) is a very interesting technique for artwork characterization purposes. However, the fact that the spectra obtained are a mixture of surface (specular) and volume (diffuse) reflection is a significant drawback. The physical and chemical features of the artwork surface may produce distortions in the spectra that hinder comparison with reference databases acquired in transmission mode. Several studies attempted to understand the influence of the different variables and propose procedures to improve the interpretation of the spectra. This article is focused on the application of mid-IR FORS and multivariate calibration to the analysis of easel paintings. The objectives are the evaluation of the influence of the surface roughness on the spectra, the influence of the matrix composition for the classification of unknown spectra, and the capability of obtaining pigment composition mappings. A first evaluation of a fast procedure for spectra management and pigment discrimination is discussed. The results demonstrate the capability of multivariate methods, principal component analysis (PCA), and partial least squares discrimination analysis (PLS-DA), to model the distortions of the reflectance spectra and to delimitate and discriminate areas of uniform composition. The roughness of the painting surface is found to be an important factor affecting the shape and relative intensity of the spectra. A mapping of the major pigments of a painting is possible using mid-IR FORS and PLS-DA when the calibration set is a palette that includes the potential pigments present in the artwork mixed with the appropriate binder and that shows the different paint textures.

Nonlinear microscopy looks beneath the surface of historic artwork

For the first time, it’s possible to create depth-resolved images of a painting without damaging it.

Non-invasive identification of metal-oxalate complexes on polychrome artwork surfaces by reflection mid-infrared spectroscopy

In this work a reflection mid-infrared spectroscopy study of twelve metal-oxalate complexes, of interest in art conservation science as alteration compounds, was performed. Spectra of the reference materials highlighted the presence of derivative-like and/or inverted features for the fundamental vibrational modes as result of the main contribution from the surface component of the reflected light. In order to provide insights in the interpretation of theses spectral distortions, reflection spectra were compared with conventional transmission ones. The Kramers–Kronig (KK) algorithm, employed to correct for the surface reflection distortions, worked properly only for the derivative-like bands. Therefore, to pay attention to the use of this algorithm when interpreting the reflection spectra is recommended. The outcome of this investigation was exploited to discriminate among different oxalates on thirteen polychrome artworks analyzed in situ by reflection mid-infrared spectroscopy. The visualization of the νs(CO) modes (1400–1200cm−1) and low wavenumber bands (below 900cm−1) in the raw reflection profiles allowed Ca, Cu and Zn oxalates to be identified. Further information about the speciation of different hydration forms of calcium oxalates were obtained by using the KK transform. The work proves reflection mid-infrared spectroscopy to be a reliable and sensitive spectro-analytical method for identifying and mapping different metal-oxalate alteration compounds on the surface of artworks, thus providing conservation scientists with a non-invasive tool to obtain information on the state of conservation and causes of alteration of artworks.

Using Non‐Destructive Analysis Techniques to Examine the Artworks of Taiwanese Artist Cheng‐Po Chen (1895‐1947)

AbstractThis study employed the non‐destructive techniques to analyze and examine the artworks of the Taiwanese artist Cheng‐Po Chen (1895‐1947) for disclosing the damage to Chen's artworks and determine his creation habits. Ten pieces of artworks that required restoration were examined using ultraviolet examination techniques. Based on the differences in their fluorescence characteristics, various parts of these works were shown to have been retouched, thus, original and retouched regions were distinguished. Examining these works using Infrared instrument revealed that Chen did not use charcoal to prepare drafts, and he directly applied oil paint to the canvases. Subsequently, these two examination techniques were adopted to examine sketches. The results showed that residues imprinted on them cause of storage methods were organic materials from charcoal and not carbon granules. The X‐ray examination identified numerous creations beneath the surface of several artworks. The X‐ray fluorescence spectrometer was used for elemental analysis of the pigments. The results corresponded with the pigments listed in Chen's purchase form, thus, we summarized the composition of palettes used by Chen. In general, this study acquired a considerable amount of information from the pigment examinations and established a database of the pigments that Chen commonly employed in his artworks.

An Interactive Local Flattening Operator to Support Digital Investigations on Artwork Surfaces

Analyzing either high-frequency shape detail or any other 2D fields (scalar or vector) embedded over a 3D geometry is a complex task, since detaching the detail from the overall shape can be tricky. An alternative approach is to move to the 2D space, resolving shape reasoning to easier image processing techniques. In this paper we propose a novel framework for the analysis of 2D information distributed over 3D geometry, based on a locally smooth parametrization technique that allows us to treat local 3D data in terms of image content. The proposed approach has been implemented as a sketch-based system that allows to design with a few gestures a set of (possibly overlapping) parameterizations of rectangular portions of the surface. We demonstrate that, due to the locality of the parametrization, the distortion is under an acceptable threshold, while discontinuities can be avoided since the parametrized geometry is always homeomorphic to a disk. We show the effectiveness of the proposed technique to solve specific Cultural Heritage (CH) tasks: the analysis of chisel marks over the surface of a unfinished sculpture and the local comparison of multiple photographs mapped over the surface of an artwork. For this very difficult task, we believe that our framework and the corresponding tool are the first steps toward a computer-based shape reasoning system, able to support CH scholars with a medium they are more used to.

Watershed Cuts: Thinnings, Shortest Path Forests, and Topological Watersheds

We recently introduced watershed cuts, a notion of watershed in edge-weighted graphs. In this paper, our main contribution is a thinning paradigm from which we derive three algorithmic watershed cut strategies: The first one is well suited to parallel implementations, the second one leads to a flexible linear-time sequential implementation, whereas the third one links the watershed cuts and the popular flooding algorithms. We state that watershed cuts preserve a notion of contrast, called connection value, on which several morphological region merging methods are (implicitly) based. We also establish the links and differences between watershed cuts, minimum spanning forests, shortest path forests, and topological watersheds. Finally, we present illustrations of the proposed framework to the segmentation of artwork surfaces and diffusion tensor images.

Portable Equipment for Luminescence Lifetime Measurements on Surfaces

The prototype of a portable instrument, based on the time-correlated single-photon counting method, purposely assembled for in situ measurements of luminescence lifetimes on artwork surfaces, is here presented. Preliminary tests have been carried out using the portable instrument and the results have been compared with those obtained using a bench instrument. In this way we have proven that the prototype provides lifetime measurements with good precision. It is also shown that fluorescence lifetime determinations, coupled with steady-state fluorescence spectra, allow the distinguishing, on laboratory samples, of different red organic lakes having similar fluorescence spectra, achieving new boundaries in the nondestructive diagnosis of artwork materials. The first in situ application of the technique on an original work of art, The Book of Kells, held at Trinity College Library, Dublin, highlighted the diagnostic potential of coupled steady-state and time-resolved luminescence spectroscopy in the identification of organic colorants.

A Note on the Reversibility of Cellulose Ethers. Detection on Artwork Surfaces Using Modified FTIR

Afin d'evaluer la possibilite reelle de reversibilite des ethers de cellulose appliques au papier dans le cadre d'une mesure de conservation ou de restauration on a etudie la presence de ces substances au moyen d'une variante de la spectroscopie FTIR transmettant de la lumiere diffuse. Les spectres infrarouges des polymeres de cellulose ethylique montrent une bande nette a 2900 cm -1 , les CH, associee a une longue vibration et une large bande a plus forte longueur d'ondes qui correspond aux modes des groupes OH. Les echantillons de papier sur la surface desquels un ether de cellulose a ete applique manifestent un plus grand accroissement de bandes CH que OH. Ceci peut etre exprime par la relation entre l'intensite des bandes OH et CH (rapport IOH/ICH). Ce calcul a ete effectue au cours de trois series d'experiences: avec du papier n'ayant subi aucun traitement, avec du papier sur lequel des ethers de cellulose avaient ete appliques et avec du papier sur lequel des ethers de cellulose avaient ete appliques puis retires par immersion dans de l'ethanol. Les resultats ont demontre que les substances appliquees n'ont pu etre completement retirees. Par ailleurs on a constate que la quantite de substances retirees n'etait pas directement proportionnelle a la duree d'immersion dans le solvant.

Laser interference-based techniques and applications in structural inspection of works of art

Techniques based on laser interferometry principles provide great potential to retrieve imperceptible bulk information regarding the physical and mechanical condition of complex and inhomogeneous structures. This review presents the progress in and prospects for optical coherent interferometry techniques in artwork conservation applications, in particular concerning the performance of the developed instrumentations and methodologies. Each of the state-of-the-art techniques is introduced by reference to fundamental principles, basic equations and general optical geometry. In this context, a brief introduction to fundamental principles governing the optical coherent interferometry measurements is presented prior to discussion on performance. Some exemplary results demonstrating that bulk interferometric signals can be obtained from rough artwork surfaces are shown and their suitability is reviewed. Several opportunities for art conservation research and applications are summarised and discussed.

Fluorescence lifetime imaging for the analysis of works of art: application to fresco paintings and marble sculptures

We have recently developed a portable system for advanced fluorescence investigation of works of art. The system is based on the measurement of both the time dependent and spectral features of fluorescence emission, after excitation with UV laser pulses. The technique is aimed at localising and identifying organic and inorganic compounds present on the surface of artworks. The time dependence of the emission is analysed with a fluorescence lifetime imaging apparatus, which allows us to measure the map of the fluorescence lifetime, combined with a portable spectrometer for recording fluorescence spectra of selected points. The characterization of the compounds present on the art object's surfaces is carried out with analytical measurements on micro-samples collected with the assistance of the fluorescence maps. These methods have been successfully applied to characterise the fresco paintings of Filippo Lippi in the cathedral of Prato and to study the contaminants on the surface of Michelangelo's David in F...

Fluorescence Lifetime Imaging and Fourier Transform Infrared Spectroscopy of Michelangelo'sDavid

We developed a combined procedure for the analysis of works of art based on a portable system for fluorescence imaging integrated with analytical measurements on microsamples. The method allows us to localize and identify organic and inorganic compounds present on the surface of artworks. The fluorescence apparatus measures the temporal and spectral features of the fluorescence emission, excited by ultraviolet (UV) laser pulses. The kinetic of the emission is studied through a fluorescence lifetime imaging system, while an optical multichannel analyzer measures the fluorescence spectra of selected points. The chemical characterization of the compounds present on the artistic surfaces is then performed by means of analytical measurements on microsamples collected with the assistance of the fluorescence maps. The previous concepts have been successfully applied to study the contaminants on the surface of Michelangelo's David. The fluorescence analysis combined with Fourier transform infrared (FT-IR) measurements revealed the presence of beeswax, which permeates most of the statue surface, and calcium oxalate deposits mainly arranged in vertical patterns and related to rain washing.

Biotechnology applied to cultural heritage: biorestoration of frescoes using viable bacterial cells and enzymes

To set up and employ, for the biorestoration of cultural heritage (altered frescoes), an advanced and innovative biotechnology method based on the sequential use of whole viable bacterial cells and specific enzymes. The bioremediation intervention consisted of the direct application onto an artwork surface of whole bacterial cells of the Pseudomonas stutzeri A29 strain (bioaugmentation), followed by, in a final step, a purified Protease enzyme. The bioremediation was performed on a Spinello Aretino fresco that had become altered by the animal glue residues of past restoration. For the reader's interest the fresco is the 14th century Conversione di S. Efisio e battaglia (Conversion of S. Efisio and battle), size 3.5 x 7.8 m at the Pisa Camposanto Monumentale, Italy. An assessment was made of the final costs of the biological tests (whole bacterial cells, enzymes) so as to compare them with other intervention techniques. A successful innovative biological approach to recover valuable frescoes was set up, and the best conditions for treatment efficiency were identified. Furthermore the cost of the biological cleaning using viable bacterial cells and enzymes (P. stutzeri, Protease, Collagenase, 1 : 3 : 10, ratio respectively) was much lower than that of other conventional methods, making this biotechnology not only very interesting but also very competitive. New biotechnologies with an innovative, soft approach to the 'biocleaning' and 'biorestoration' of cultural heritage are in constant demand, and our results are clear evidence that such an approach has been achieved; the technique could be of significant importance towards developing other goals.

LIBS used as a diagnostic tool during the laser cleaning of ancient marble from Mediterranean areas

The use of laser ablation for cleaning stone is a tried-and-tested method for preserving outdoor artwork surfaces exposed to environmental stresses. However, it is of interest to spectroscopically characterize the sample surface before and during the laser ablation in order to implement automatic control of the cleaning process. To this aim, we have undertaken systematic LIBS analysis on various clean and dirty surfaces of marble fragments collected from ancient quarries in Mediterranean areas, without the characteristic patina that comes from the protective layers usually deposited on the final artwork. The effectiveness of the cleaning process was then monitored by following the disappearance from the LIBS spectra of the encrustation elements during successive laser shots. The LIBS analysis of the clean surfaces of the samples examined confirmed that main bulk composition is based on calcium and magnesium carbonates, with the addition of strontium and, to a minor extent, of manganese and copper substituents. On the other hand, the encrustations were rich in sodium, aluminum, iron, silicon, titanium, lithium, manganese, and chromium, probably coming from sand/soil deposition and, only to a minor extent, from atmospheric pollution. Although SEM imaging and SEM-EDX analyses performed on the same samples at different resolutions showed remarkable surface inhomogeneities from the crustal region deep into the bulk material, the work demonstrates the possibility of a quantitative, minimally invasive, LIBS stratigraphy. The results from the technique are suitable for monitoring cleaning processes by determining appropriate elemental markers present on the surface at trace level (of the order of 100 ppm).

Low-cost sensor system for online monitoring during laser cleaning

The self-limiting effect during laser cleaning only occurs in a limited amount of specific applications in restoration (e.g. removal of black crust from white marble). In all the other cases, a control of the removal process will be necessary either by the operator himself or by the employment of sensor equipment. Various methods, mainly spectroscopic (e.g. LIBS), have been investigated and proposed by others. Despite the fact that these have been shown to be promising, they all have in common rather high investment cost close to that of the cleaning equipment. Furthermore, this highly sophisticated control equipment is not easy to handle by conservators in practice. As an alternative low-cost method, we employed a simple photodiode to detect the scattered light from the irradiation area on the artwork surface. In many cases, this signal contains several pieces of information on the layer just being removed. The scattered radiation detected by the photodiode originates from the laser-induced plasma as well as reflected laser radiation. A separation, if necessary in order to separate the information, is possible by spectral filters. First applications during laser cleaning of corroded metal, encrusted glass and stone were promising. It has turned out that there is a distinct influence on the scattered light amplitude or even the pulse-bandwidth once the laser has removed the encrustation completely. The corresponding signal can be used in a closed loop control or for online monitoring.