Visible and infrared imaging spectroscopy of paintings and improved reflectography

Abstract

Background: Imaging spectroscopy, the collection of spatially co-registered images in many contiguous spectral bands, has been developed for remote sensing of the Earth utilizing reflectance or luminescence. In this paper we summarize findings on the application of imaging spectroscopy to works of art in order to identify and map artists' pigments, improve the visualization of preparatory sketches, and identify non-original material.Methods: Two types of novel hyperspectral cameras, one operating from the visible to near-infrared (VNIR, 400-900 nm) and the other in the shortwave infrared (SWIR, 950-1700 nm), have been used to collect diffuse reflectance spectral image cubes from a variety of paintings. The resulting cubes (400-1700 nm, 310 spectral bands) were calibrated to reflectance and the resulting spectra compared with point-based spectra collected with a fiber reflectance spectrometer (350-2500 nm). In addition, a calibrated multispectral camera (600-950 nm, eight spectral bands) was used to obtain luminescence spectral image cubes after exciting paintings at blue wavelengths.Results: False-color images obtained from the SWIR imaging system are shown to give improved visualization of changes from paintings having large and complex reworkings, e.g. Pablo Picasso's The Tragedy (1903). False-color images and reflectance spectra allowed definitive identification of restoration in a late 13th century Sienese painting that cannot be seen by traditional infrared reflectography. Spectral image processing on the reflectance image cubes have been used to identify the primary pigments or pigment mixtures. For example, the primary pigments and their distribution in Picasso's Peonies (1901) was determined and compared with x-ray fluorescence (XRF) analysis and scanning electron microscopy-energy dispersive x-ray spectroscopy (SEM-EDS). Conclusion:The results show that the combination of both the SWIR reflectance data and the luminescence data provides a more robust ability to assign the pigments than with visible spectroscopy alone. Also highlighted is the utility of reflectance imaging spectroscopy in the SWIR region to better reveal specific paint changes, including changes in the drawings and markings made by the original artist, or changes made by a subsequent conservator such as a fill.

Comparing the effectiveness of hyperspectral imaging and Raman spectroscopy: a case study on Armenian manuscripts

“…This then allows one to examine and map the entire surface of an object [6,34,38] and guides the use of techniques such as Raman spectroscopy [39,40], XRF [41,42], and FORS [43] which give a more detailed analysis [14,[44][45][46]. This methodology can overcome concerns that point-based analyses may not represent the whole and may not be sufficient to demonstrate the diversity of colourants in such works [3].…”

“…The spectra produced can be used to characterise the materials at the surface of the image and produce maps of these materials, but hyperspectral imaging has also been used to reveal hidden images and text, given its ability to detect reflectance at many wavelengths, often including wavelengths outside of the visible range [1,32]. Originally a remote sensing technique [32] it has been developed over the years for astrophysics, military applications, medical imaging, and more recently for the nondestructive investigation of works of cultural heritage [6,[33][34][35]. HSI has been successfully applied to a range of heritage material including The Declaration of Independence [36] where alterations to text were revealed, and Edvard Munch's "The Scream" where the pigments used were characterised and mapped [37].…”

“…Scientific techniques have been applied to pigment identification as part of conservation since the late twentieth century [1,2] aiding: characterisation of the palette of an artist or workshop [3,4]; art historical understanding of the artist [5]; identification of restorations or interventions [3,6]; monitoring degradation [7]; detailing the conservation state of an item [3]; revealing preparatory sketches [6], underdrawings [3], or palimpsests [8]; segmentation of a painting into regions for differential processing such as colour retouching [9]. Such knowledge is of value to researchers and can also aid in effective conservation strategies and restoration [7], and answer questions of provenance [3,4,6,7,[10][11][12]. In the broader sense it can also help determine trade routes and cultural interactions [12,13], and give some idea of the technology of the period with respect to pigment manufacture [12,13].…”

Use of infrared hyperspectral imaging as an aid for paint identification

“…HSI is already recognised as a valuable technique in the art world and it has been successfully used for mapping of different paints in the art work, 4,5 material identiication [6][7][8][9] and analysis of the artists' techniques. 10,11 Recently, an application of mid-IR imaging device for art work analysis was also demonstrated.…”

IR Reflectography and Active Thermography on Artworks: The Added Value of the 1.5–3 µm Band

“…Beyond the traditional diagnostic methods such as reflectography and thermography, selective multi-spectral analysis in the near-infrared region (IR-A) has recently been demonstrated to be a promising tool for investigating pictorial layers [2,3]. Within this work, infrared radiation is divided according to the international Commission on Illumination (CIE) and sensor response scheme as presented in Table 1 [4].…”