New Advances in the Application of FTIR Microscopy and Spectroscopy for the Characterization of Artistic Materials

Abstract

Fourier transform infrared (FTIR) spectroscopy is one of the most widely applied techniques for the investigation of cultural heritage materials. FTIR microscopy is well established as an essential tool in the microdestructive analysis of small samples, and the recent introduction of mapping and imaging equipment allows the collection of a large number of FTIR spectra on a surface, providing a distribution map of identified compounds. In this Account, we report recent advances in FTIR spectroscopy and microscopy in our research group. Our laboratory develops, tests, and refines new and less-studied IR spectroscopy and microscopy methods, with the goal of their adoption as routine analytical techniques in conservation laboratories. We discuss (i) the analysis of inorganic materials inactive in the mid-IR region by means of far-IR spectroscopy, (ii) the development of new methods for preparing cross sections, (iii) the characterization and spatial location of thin layers and small particles, and (iv) the evaluation of protective treatments. FTIR spectroscopy and microscopy have been mostly used in the mid-IR region of 4000-600 cm(-1). Some inorganic pigments, however, are inactive in this region, so other spectroscopic techniques have been applied, such as Raman spectroscopy. We suggest an alternative: harnessing the far-IR (600-50 cm(-1)). Our initial results show that far-IR spectroscopy is exceptionally useful with mural paintings or with corrosion products from which larger sample quantities can generally be collected. Moreover, the inorganic composition of a sample can be characterized by the presence of several compounds that are inactive in the mid-IR range (such as sulfides, oxides, and so forth). Stratigraphical analyses by FTIR microscopy can be hindered by the process of cross section preparation, which often involves an embedding organic polymer penetrating the sample's porous structure. Here, the polymer bands may completely cover the bands of organic compounds in the sample. However, a correct methodological approach can prevent such limitations. For example, it is always advisable to analyze the sample surface before preparing the cross section in order to characterize the preparation layers and the varnish layers, which are generally applied to the surface of a painting both to protect it and improve the color saturation. Furthermore, the innovative use of IR-transparent salts as embedding material for cross sections can prevent contamination of the embedding resin and improve detection of organic substances. Another key point in the use of FTIR microscopy in artwork analysis is spatial resolution. The high-energy output of a new integrated FTIR microscope enhances the ability to characterize and spatially locate small particles and thin layers. Moreover, the new configuration proves extremely useful in the evaluation of protective treatments, because larger areas may be analyzed in less time in comparison to traditional systems, allowing the collection of more statistical data.

Thermal oxidation and nitridation of sputtered Zr thin film on Si via N2O gas

“…Sample of assputtered Zr on Si does not show any detectable peak of Zr-Zr and/or Zr-Si. This is because those inorganic bonds are inactive in region of mid-infrared (4000-400 cm −1 ) [53,54]. For oxidized samples, transmittance bands of Zr-O vibration mode are detected at around 440 and 580 cm −1 and it is associated with ZrO 2 [55][56][57][58].…”

Study of Late Roman and Byzantine glass by the combined use of analytical techniques

“…In the last decades analytical techniques usually employed to characterize the condensed matter, were optimized for application in the study of materials relevant to cultural heritage [1][2][3][4]. In order to preserve the integrity as well as the aesthetic value of artistic objects, micro-destructive and non-destructive techniques are preferred [5][6][7][8].…”

Polychromic structures and pigments in Guangyuan Thousand-Buddha Grotto of the Tang Dynasty (China)

“…Some of them are very effective for pigment identification in the special case study, such as reflection visible light imaging microspectroscopy ( Van der Weerd et al, 2003), X-ray microspectroscopy (Cotte et al, 2006(Cotte et al, , 2007, particle induced X-ray emission spectroscopy (PIXE) (De Viguerie et al, 2009), X-ray diffraction (XRD) (Correia et al, 2008;Van der Snickt et al, 2009;Brostoff et al, 2009), X-ray fluorescence (XRF) (Dik et al, 2008;Castro et al, 2008), Fourier transform infrared (FT-IR) spectroscopy (Prati et al, 2010) (attenuated total reflection Fourier transform infrared (ATR-FT-IR) (Marendo et al, 2005;Mazzeo et al, 2007;Mateo et al, 2009) or synchrotron radiation Fourier transform infrared (SR-FT-IR) (Salvado et al, 2005)), Raman spectroscopy (RS) (Ospitali et al, 2006;Hernanz et al, 2006;Bersani et al, 2004), scanning electron microscopy coupled with electron beam microprobe analysis using an energy-dispersive X-ray detector (SEM-EDX) (Colombini et al, 2004;Mazzeo et al, 2004;Peris-Vicente et al, 2009), polarized light microscopy (PLM) (Burgio et al, 2005), and so on. However, the characterization of artistic materials is rather complicated not only because the sample-gathering is restricted on an exceedingly small scale, but also because the samples consist of a complex superimposition of different layers but each being composed of several pigments mixed together (Schmidt et al, 2009;Maravelaki-Kalaitzaki and Kallithrakas-Kontos, 2003).…”