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Multi-step Approach for Characterization of Artworks Based on Hyperspectral Imaging and Complementary Techniques
Abstract
This paper presents an optimized approach for the characterization of complex painting layers and for the evaluation of previous interventions on artworks. Focusing on the capabilities of hyperspectral imaging, which combines spectral and imaging data, this specific approach reflects also the importance of complementary methods and techniques, which have the ability to complete and to validate the results. Following the unique character of the artworks, our goal is to emphasize the importance of data association for the characterization of complex structures such as pictorial layers. The case study for our application was represented by an artwork attributed to Stefan Luchian, one of the most representative Romanian modern artist from the beginning of the 20th century. By combining hyperspectral data with multispectral analysis, high resolution digital X-ray and XRF we were able to develop a multi-step approach that can accurately document the key aspects regarding the state of conservation, the execution technique, and also the features related to previous interventions. Moreover, by correlating the aspects highlighted earlier we were able to use the resulted data for the artwork authentication.
... This approach makes the description of the artwork much more precise and richer in details since it individualizes not only its components, support, and coating materials, but also the context in which they were used. The wisdom in better bringing together the analytical resources available and performing the analyses required by each case determines the success of a forensic examination of a forgery or the authenticity of a work of art [8]. ...
In 2008, Nicolas Eastaugh, founder and chief researcher at Art Discovery, a renowned London company for the analysis and research of artwork, discovered the presence of the white titanium (titanium dioxide) pigment in a painting attributed to the Dutch naturalized expressionist artist Heinrich Capendonk. The work had reached a record value of EUR 2.4 million at an auction in 2006. However, in 1915, the year in which the work was supposed to have been created, white titanium was not even available for use as a pigment, which would happen about 20 to 30 years later. The analytical result achieved by Eastaught revealed one of the biggest schemes of artwork forgeries ever discovered. The forger, Wolfgang Beltracchi, made a fortune, (under)estimated at EUR 30 million, built over 25 years acting in the art market. There are several cases of counterfeiting schemes involving artwork, large fortunes, renowned galleries, museums, collectors, specialists, and masterpieces. Cases like the one revealed by Eastaugh's analyses or the millionaire counterfeit scheme involving the century-old North American Knoedler Gallery are illustrative examples of how the art market is vulnerable to this kind of crime. The International Monetary Fund (IMF) and the United Nations Office on Drugs and Crime (UNODC) estimated the total annual trade in art and antiques in 2018 at around USD 70 billion, of which about USD 6 billion may have been due to illegal transactions related to theft, counterfeiting, smuggling, and organized crime. Still according to those institutions, half of that amount involved financial crimes and money laundering. In Brazil, within the scope of the Lava Jato Operation, the Federal Police seized 842 pieces of art and historical and cultural heritage, including paintings from different historical periods, sculptures, and other pieces, which add up to an estimated value of over BRL 33 million. All the pieces were related to investigations involving money laundering in cases of active and passive corruption. As other forms of money laundering resulting from various crimes have been curtailed by world authorities through specific legislation, the art market world has become increasingly attractive to crime. This scenario, combined with the great financial relevance of the legitimate art market, caused a very considerable increase in the demand for works by renowned authors and, as a direct consequence, a proportional increase in the number of forgeries and adulterations. As a result, the quality of counterfeits has also experienced a great improvement, requiring a proportional gain in technology and expertise in forensic analysis and authentication fields. Similarly, the high speculation in prices of artworks also increased the interest in new and advanced analytical techniques for determining authenticity, authorship, origin, and materials used by the authors. The refinement of counterfeiting and adulteration techniques has demanded a multidisciplinary and technological approach to the authentication process, and, at this point, we are faced with a considerable degree of complexity in the already difficult process of authenticating works of art. The authorship or authenticity determination of a painting is unavoidably based on a triangle formed by three disciplines: art history, preservation sciences, and materials sciences. The voices of our benches and equipment are unlikely to be able, on their own, to unequivocally conclude the authenticity of a work of art. Likewise, the most trained eyes of a professional connoisseur are no longer able to face the most astute counterfeiters. The best results of authenticity studies will always be achieved when these three distinct disciplines come together and complement each other in the search for comprehensive, technical, and artistic knowledge about the work. In addition to the historical study of the piece, the physical–chemical characterization of materials and components or elementary and multispectral imaging become powerful tools for fraud detection and even characterization and individualization of the authentic piece. The simplest techniques, generally used for initial documentation, to the more complex, analytical resources are used to extract the greatest amount of information from the different parts that make up a painting. In its diverse and complex layers, from the support to the final coating, paintings are composed of multilayers of heterogeneous mixtures of varied organic and inorganic compounds. A thorough investigation of this scenario always requires the use of advanced and combined techniques to better understand each case, depending on their nature. The analysis of the painting surface by a stereo-microscope will reveal genuine—or artificially produced—craquelure or brushwork patterns compatible with the artistic style proposed by the author of the work. Likewise, the UV fluorescence properties of the painting may differentiate between old and new additions of paint to the piece. However, it is in the deepest layers of an artwork that the most sophisticated analytical techniques contribute most incisively. X-ray radiography and infrared reflectography, coupled with ultra-sensitive charge-coupled devices (CCD), began to detect underdrawings that were invisible to the previously available methods. Several works have demonstrated the usefulness of tools such as synchrotron radiation, microimaging by X-ray fluorescence (XRF), and Raman or Fourier-transform infrared (FTIR) spectroscopies, combined with the versatility of portable spectrometric identification techniques, where pigment particles less than 1 micrometer in diameter can be analyzed. Even the power of pyrolysis-gas chromatography-mass spectrometry (Py-GC-MS) to identify novel synthetic organic polymers, which greatly assists in the analyses of pigments, coatings, binders, and other painting components, can, in many cases, reveal anachronisms present in the counterfeits. Other techniques such as laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS), isotope-ratio mass spectrometry (IRMS), and accelerator mass spectrometry (AMS) allow for the determination of isotopic ratios of heavy and light elements, which are decisive to determining the geographical origin of some pigments and the age of a painting canvas or its wooden frame. Such techniques used in association with multivariate analysis tools, artificial intelligence, and machine learning help achieve increasingly conclusive results, requiring less time and effort from the entire team of researchers. Each of the analytical techniques, evaluated for their versatility, resolution power, type of information generated, portability, and employment, have the potential for greater use in combined and multimodal work. This approach makes the description of the artwork much more precise and richer in details since it individualizes not only its components, support, and coating materials, but also the context in which they were used. The wisdom in better bringing together the analytical resources available and performing the analyses required by each case determines the success of a forensic examination of a forgery or the authenticity of a work of art. It is not hard to see that it is unlikely that a single company or laboratory, whether public, private, academic, or not, will own all the technological resources to exhaust such an analysis. Furthermore, it is not uncommon for crimes involving works of art to be transnational. All this leads us to the last step of our range of complexity: laboratories, museums, forensic, and research institutes involved in examining the authenticity of artworks should operate on secure and integrated networks, generating data that is widely shared between partner institutions. Several institutes in the world already work in this way, such as INTERPOL, the INTERNATIONAL COUNCIL OF MUSEUMS (ICOM), the Federal Bureau of Investigation (FBI), UNODC, and the Integrated Platform for the European Research Infrastructure on Cultural Heritage (Iperion CH). This has proven to be one of the most effective ways to curb this type of crime, which, sneakily, erodes our history and cultural heritage.
The study of paintings using a multi-sensor approach allows obtaining information on details not visible to the naked eye, such as pentimenti and preparatory drawings. The possibility to concatenate multispectral images, coming from different devices and spectral ranges (from visible to short-wave infrared), allows the creation of hypercube data that can be analysed with chemometric approaches, such as Principal Components Analyses (PCA). Moreover, the use of X-Ray radiation performing radiographic images allows us to reach the inner layers and to detect details of the paintings that are not accessible using optical radiations. In this work, “The Spring” painting, realised by Mario de’ Fiori e Filippo Lauri, was analysed by using a multi-sensor approach: a full spectrum Nikon camera, an InGaAs camera and an Image Plate detector for X-rays to recover hidden details of the artists’ creative process.
The literature on the application of Multispectral and Hyperspectral imaging for identification of pigments on artworks is sparse. While these methods do not provide the analytical capability that spectroscopies do offer, the use of spectral imaging has the advantage of being a rapid and relatively low-cost solution for the examination of large areas. This paper presents a flowchart for the identification of historical pigments applied with gum Arabic using multispectral imaging (wavelength ranging from 360 to 1700 nm) performed with a modified digital camera for infrared, visible and ultraviolet photography; and an InGaAs camera for infrared reflectography. The flowchart method will be most successful on paint made of one layer of pure pigment, and it can selectively discriminate only a fraction of the 56 pigments analyzed. Though, considerably limited in its analytical capabilities, the low cost and speed of the workflow make the method worthwhile, even if only to localize retouching and areas appearing the same hue but painted with different pigments. The InGaAs camera is the only expensive instrument used in this study but its cost is relatively affordable for the average painting conservation studio since only a model with a low pixel count is required (320×256 pixels) rather than a more sophisticated InGaAs scanner system.
Multispectral imaging has been applied to the field of art conservation and art history since the early 1990s. It is attractive as a non-invasive imaging technique because it is fast and hence capable of imaging large areas of an object giving both spatial and spectral information. This paper gives an overview of the different instrumental designs, image processing techniques and various applications of multispectral and hyperspectral imaging to art conservation, art history and archaeology. Recent advances in the development of remote and versatile multispectral and hyperspectral imaging as well as techniques in pigment identification will be presented. Future prospects including combination of spectral imaging with other non-invasive imaging and analytical techniques will be discussed.
A method has been developed to detect underdrawings in paintings more completely than is possible with ir photography. A modified Barnes ir camera has been used equipped with a lead sulfide detector. The results can be explained in terms of an increase in hiding thickness of paint layers with the wavelength. Practical aspects of reflectography of paintings are briefly described and an example is given.
Spectrograph-based spectral imaging systems provide images with a large number of contiguous spectral channels per pixel. This paper describes the calibration and characterisation of such systems. The relation between pixel position and measured wavelength has been determined using three different wavelength calibration sources. Results indicate that for spectral calibration, a source with very narrow peaks, such as a HgAr source, is preferred to narrow band filters. A third-order polynomial model gives an appropriate fit for the pixel to wavelength mapping. The signal-to-noise ratio (SNR) is determined per wavelength. In the blue part of the spectrum, the SNR is lower than in the green and red part. This is due to a decreased quantum efficiency of the sensor, a smaller transmission coefficient of the spectrograph, as well as low output power of the illuminant. Increasing the amount of blue light, using an additional fluorescent tube with a special coating considerably increases the SNR. Furthermore, the spatial and spectral resolution of the system has been determined in relation to the wavelength. These can be used to choose appropriate binning factors to decrease the image size without losing information. In our case this could reduce the image size by a factor of 60 or more.
While books on the medical applications of x-ray imaging exist, there is not one currently available that focuses on industrial applications. Full of color images that show clear spectrometry and rich with applications, X-Ray Imaging fills the need for a comprehensive work on modern industrial x-ray imaging. It reviews the fundamental science of x-ray imaging and addresses equipment and system configuration. Useful to a broad range of radiation imaging practitioners, the book looks at the rapid development and deployment of digital x-ray imaging system.
The fluorescence under ultraviolet light of oil-paints and some picture surfaces has been studied with a fluorescence spectrometer. The development of fluorescence and the yellowing of linseed oil appear to be greatly influenced by the presence of pigments. Some pigments have an inhibiting, some an enhancing effect, and some are indifferent. In the light of these results and the material published before, the fluorescence of some picture surfaces is discussed.
Compared to conventional imaging spectrometry, coded aperture snapshot spectral imaging (CASSI) has the advantages of high throughput snapshot imaging etc. But because of the presence of the dispersive element, CASSI system suffers the effect of the same optical aberrations as traditional single slit spectrometer. To study the effect of keystone on signal acquisition, the model of spatial-spectral aliasing and the reconstructed result in CASSI system, combined with the principle of coded aperture spectral imaging and the reconstruction algorithm, the relative peak signal-to-noise ratio (PSNR) of the reconstructed image and the maximal error of the reconstructed spectral curve at different spectral band bending were calculated and analyzed. The experimental result showed that spectral band offset of the signal acquired by the detector will change the degree of spatial-spectral aliasing. Compared to the reconstructed results with no spectral band bending, distinct errors are exhibited when spectral band bending emerges. And the reconstructed spectral curve tends to be smooth on both sides of the spectral channel. In order to reconstruct the spectral cube with high accuracy, spectral band offset should be no more than half a pixel.
Spectral imaging technology, which records simultaneously spectral and spatial information about an object, was initially developed for remote sensing and has since been successfully applied to other areas of research. Although relatively new to the field of conservation, this non-invasive method of investigation has already provided promising results in the analysis of paintings and written documents, the characterization of materials and digital documentation. This article reviews the published literature relating to the application of multispectral and hyperspectral imaging for the study and conservation of works of art and presents some new perspectives offered by this innovative and fast-developing technology.
Hyperspectral imaging generates an accurate digital record for art conservation. This may be used for monitoring change or damage to paintings, as digital documentation resists deterioration better than photographs. Also, digital imaging can assist in the restoration of artwork. It has already been applied to assessing damage from laser cleaning, where computer-aided comparison of before and after cleaning the images have provided superior results. Finally, digital imaging assists in discovering the history of a piece of art by revealing underdrawings and retouchings. Thus, multiple analysis objectives may be achieved simultaneously, which previously required several different instrumental techniques.A number of applications of this technique are given. In particular, studies of blue pigment in Sydney Nolan and Ivor Hele paintings will be described. The use of the technique to monitor the degradation of varnish on paintings is discussed.
A Novel Infra-Red Camera for Art Gallery Work
- rawlins
Rawlins, F., I., G., " A Novel Infra-Red Camera for Art Gallery
Work", The Museum Journal, vol. XXXVIII, 1938, pp.186-187
High Resolution Vis And Nir Reflectography By Digital CCD Telescope And Imaging Techniques: Application To The Fresco "Vergine Con Bambino
- Ivan Roselli
- Pierluigi Testa
Ivan Roselli, Pierluigi Testa, "High Resolution Vis And Nir
Reflectography By Digital CCD Telescope And Imaging Techniques:
Application To The Fresco "Vergine Con Bambino" In S. Pietro In
Vincoli, Rome", 8th International Conference on "Non Destructive
Investigations and Micronalysis for the Diagnostics and Conservation
of the Cultural and Environmental Heritage." Lecce (Italy), May
2005.
Effect of keystone on coded aperture spectral imaging
- Qun-Bo Lu-Lu Qian
- Min Lü
- Huang
Lu-lu Qian, Qun-bo Lü, Min Huang, Qi-sheng Cai, Bin Xiang-li,
"Effect of keystone on coded aperture spectral imaging", Optik 127,
2016, pp. 686-689.
Advances in multispectral and hyperspectral imaging for archaeology and art conservation
- Haida Liang
Haida Liang, "Advances in multispectral and hyperspectral imaging
for archaeology and art conservation", Applied Physics A, February
2012, Vol. 106, Issue 2, pp. 309-323.