Reflectance Imaging Spectroscopy Research Articles

Discovery of pararealgar and semi-amorphous pararealgar in Rembrandt's The Night Watch: analytical study and historical contextualization

This article reports on the discovery of pararealgar and semi-amorphous pararealgar in Rembrandt's masterpiece The Night Watch. A large-scale research project named Operation Night Watch was started in 2019. A variety of non-invasive analytical imaging techniques, together with paint sample research, has provided new information about Rembrandt's pigments, materials, and techniques as well as the current condition of the painting. Macroscopic X-ray fluorescence, macroscopic X-ray powder diffraction and reflectance imaging spectroscopy identified the presence of arsenic sulfide pigments and degradation products of these pigments in the doublet sleeves and embroidered buff coat worn by Lieutenant Willem van Ruytenburch (central figure to the right of Captain Frans Banninck Cocq). Examination by light microscopy of two paint samples taken from this area shows a mixture of large sharp-edged tabular yellow and orange to red pigment particles, and scanning electron microscopy-energy dispersive X-ray analysis identified these particles as containing arsenic and sulfur. Using micro-Raman spectroscopy, the yellow particles were identified as pararealgar, and the orange to red particles as semi-amorphous pararealgar. Synchrotron-based X-ray diffraction allowed visualization of the presence of multiple degradation products associated with arsenic sulfides throughout the paint layer. The discovery of pararealgar and semi-amorphous pararealgar is a new addition to Rembrandt's pigment palette. To contextualize our findings and to hypothesize why, how, and where Rembrandt obtained the pigments, we studied related historical sources. A comprehensive review of historical sources gives insight into the types of artificial arsenic sulfides that were available and suggests that a broader range of arsenic pigments could have been available in Amsterdam in the seventeenth century than previously thought. This is supported by the use of a very similar mixture of pigments by Willem Kalf (1619–1693), a contemporary artist based in Amsterdam. Together with the condition of the particles in the paint cross sections, this brings us to the conclusion that Rembrandt intentionally used pararealgar and semi-amorphous pararealgar, together with lead–tin yellow and vermilion, to create an orange paint.

Advanced imaging to recover illegible text in historic documents. The challenge of past chemical treatments for ink enhancement

From fires to floods, from invisible inks to redactions, information has been accidentally or intentionally obscured on countless documents, maps and photographs, in collections from archives, libraries, and museums across the world. Removed from catalogues and reading rooms and therefore inaccessible to researchers and the general public, what new knowledge would these obscured documents reveal if we were able to read them? This paper demonstrates that current imaging technologies can be used to unlock this lost content.We used High Resolution Multiband Imaging (MBI), Reflectance Imaging Spectroscopy (RIS) and micro X Ray Fluorescence (µXRF) imaging to reveal illegible letter-forms and whole words written in iron gall ink on parchment from medieval documents relevant to the 'Virtual Record Treasury of Ireland' project, a digital reconstruction of archives destroyed in 1922 at the Public Record Office of Ireland at the outset of the Irish Civil War.The readability of text in historic documents with faded iron gall ink and/or parchment obscured by damp stains and ingrained dirt was successfully enhanced with MBI techniques, such as UV-induced visible luminescence (UVL) and UV reflected (UVR) imaging, which were able to recover the contrast of the ink. However, visualising text in documents showing chemical damage caused by the application of reagents for ink enhancement in the 19th century (a practice known as “galling”) was more challenging because of the similar composition of the ink and the staining. RIS proved helpful to read documents with moderate to severe chemical damage, particularly after applying Principal Component Analysis (PCA). Text in documents that were severely damaged by galling was also recoverable with µXRF imaging of the distribution of iron from the ink. This also posed several challenges, such as minimising movement of the parchment during overnight scans and separating the data corresponding to iron on the front of the parchment which was combined with the signal from the back. Through subtraction of elemental maps during post-processing, we managed to tackle the latter issue. The combination of these different imaging techniques enabled palaeographers and medieval records specialists to identify individual characters and whole words, thereby recovering the meaning of texts that were previously indecipherable.Further research will adapt the methodology to the broad range of causes of information loss, including other reagents historically used for ink enhancement, as well as the variety of document media and temporalities, which require an extensive and multi-faceted approach of advanced imaging and post-processing techniques, in balance with the preservation needs of these fragile and invaluable historic materials.

Seventeenth-Century Barniz de Pasto Objects from the Collection of the Hispanic Society Museum & Library: Materiality and Technology

The Hispanic Society Museum & Library (HSML) holds a collection of nine viceregal barniz de Pasto objects, made by Indigenous artisans in the 17th and 18th centuries. Designed to imitate Asian lacquers and intended for European aesthetic tastes, barniz de Pasto is an example of Indigenous technique and knowledge that has survived to the present day. An in-depth analysis of five of these barniz de Pasto objects, dated to the first half and last quarter of the 17th century based on their iconography, was carried out through a combination of non-invasive and micro-invasive techniques, including portable X-ray fluorescence (pXRF) spectroscopy to investigate the possible presence of inorganic pigments, and fiber-optics reflectance spectroscopy (FORS) and reflectance imaging spectroscopy (RIS) to provide molecular information on colorants and their distributions across the objects. Dyes and pigments were also identified using Raman spectroscopy, Fourier-transform infrared (FTIR) spectroscopy, and liquid chromatography/mass spectrometry (LC/MS). The nature of the resin was determined by FTIR and pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS), while the decoration stratigraphy and composition were analyzed by scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM-EDS). This paper confirms the use of mopa mopa, the resin used in the barniz de Pasto technique, in two objects not previously analyzed, and identifies indigo, insect-based red, calomel, lead white, and an unknown flavonol-based yellow dye, and challenges the use of calomel as a temporal marker for these works. Taken together, these results expand our understanding of the material use and explorations undertaken by artists during this time period to create such elaborate and enduring objects.

Relationship between reflectance and degree of polarization in the VNIR-SWIR: A case study on art paintings with polarimetric reflectance imaging spectroscopy

We study the relationship between reflectance and the degree of linear polarization of radiation that bounces off the surface of an unvarnished oil painting. We design a VNIR-SWIR (400 nm to 2500 nm) polarimetric reflectance imaging spectroscopy setup that deploys unpolarized light and allows us to estimate the Stokes vector at the pixel level. We observe a strong negative correlation between the S0 component of the Stokes vector (which can be used to represent the reflectance) and the degree of linear polarization in the visible interval (average -0.81), while the correlation is weaker and varying in the infrared range (average -0.50 in the NIR range between 780 and 1500 nm, and average -0.87 in the SWIR range between 1500 and 2500 nm). By tackling the problem with multi-resolution image analysis, we observe a dependence of the correlation on the local complexity of the surface. Indeed, we observe a general trend that strengthens the negative correlation for the effect of artificial flattening provoked by low image resolutions.

Spectral Mapping Techniques for the Stratigraphic and Compositional Characterisation of a 16th-Century Painting

Identifying a painting’s pigment palette is crucial for comprehending the author’s technique, as well as for evaluating the degradation of the materials. This paper investigates the stratigraphy and pigments distribution of a 16th-century painting from the Uffizi Galleries collection. Firstly, we obtained compositional information through the cross-sectional analysis of samples using scanning electron microscopy. Secondly, we performed elemental mapping using macro-X-ray fluorescence followed by reflectance imaging spectroscopy. The painting image cube was analysed using the spectral correlation mapping (SCM) classification algorithm to accurately identify the distribution and composition of the pigment mixtures.

Reflectance imaging spectroscopy for the study of archaeological pre-Columbian textiles

In this study, two pre-Columbian textiles belonging to the Middle Orizon and Necropolis Paracas Cultures are studied by means of reflectance imaging spectroscopy. The non-invasive analysis of artifacts is a fundamental step when investigating the constituent materials and their state of conservation in order to target subsequent sampling campaigns in specific areas. The paper aims to explore the spectral properties in the Visible Near-Infrared (VNIR) and Short-Wave Infrared (SWIR) intervals and investigate the spectral correlation between the relevant identified regions of interest. Two ways of selecting relevant spectral signatures are proposed: manual selection and automatic filtering. According to these two selections, the regions of interest undergo spectral unmixing in the VNIR interval to investigate which dyes had been used as such. The hyperspectral images are then mapped according to the selected endmembers in both VNIR and SWIR intervals. Small areas that feature the usage of a peculiar black thread have been given particular attention and imaged with a macro objective. The SWIR mapping on one of the samples has helped to reveal a pattern that can be ascribed to the manufacturing processes or the burial conditions.

Comparison of macro x‐ray fluorescence and reflectance imaging spectroscopy for the semi‐quantitative analysis of pigments in easel paintings: A study on lead white and blue verditer

AbstractMacroscopic x‐ray fluorescence imaging spectroscopy (MA‐XRF) and reflectance imaging spectroscopy (RIS) are important tools in the analysis of cultural heritage objects, both for conservation and art historical research purposes. The elemental and molecular distributions provided by MA‐XRF and RIS respectively, are particularly useful for the identification and mapping of pigments in easel paintings. While MA‐XRF has relatively established data processing methods based on modeling of the underlying physics, RIS data cannot be modeled with sufficient precision and its processing has considerable room for improvements. This work seeks to improve RIS data processing workflows in the short wavelength infrared range (SWIR, 1000–2500 nm) with a novel method that fits Gaussian profiles to pigment‐specific absorption features, and we compare its performance to MA‐XRF for the task of semi‐quantitative pigment mapping, evaluating their limits of detection (LODs) and the matrix effects that affect their signals. Two pigments are considered in this work, lead white and blue verditer, which are mapped in SWIR RIS using the first overtone of OH stretching of their primary compounds, hydrocerussite (Pb3(CO3)2(OH)2) and azurite (Cu3(CO3)2(OH)2), at 1447 and 1497 nm respectively, and in MA‐XRF using the Pb‐L and Cu‐K fluorescence signals. The methods are evaluated using two sets of custom‐prepared paint samples, as well as a 16th‐century painting, discussing the identification, mapping, and semi‐quantitative analysis of the considered pigments. We found SWIR RIS to be a pigment‐specific method with a longer linear range but inferior LODs and penetration depth when compared to MA‐XRF, the latter is often not capable of discriminating between different pigments with identical elemental markers. We furthermore present a novel color scale that allows the simultaneous visualization of signals above and below a confidence limit.

Francis Williams: Shedding light on the production, materials and techniques of the portrait of a Jamaican scholar

AbstractThe Victoria and Albert Museum holds an important portrait of the Jamaican scholar and writer Francis Williams (c.1692/97–1762), portrayed as a scholar in his study. It is believed to have been painted around 1745 by an unknown artist, but the circumstances of its production are unknown. A technical examination of the painting was performed using x‐radiography and infrared reflectography (IRR), macro x‐ray fluorescence scanning (XRF), digital microscopy, scanning electron microscopy with energy‐dispersive x‐ray spectroscopy (SEM–EDX) and reflectance imaging spectroscopy in the short‐wave infrared (SWIR). XRF, IRR and reflectance imaging spectroscopy in the SWIR revealed the distribution of inorganic pigments including lead white, earth pigments, Prussian blue, vermilion, orpiment (or pararealgar) and bone or ivory black. Pentimenti and a different sketched landscape were observed in the IRR images, highlighting changes in the final composition. Three‐dimensional (3D) digital microphotography provided additional historical and contextual information through the observation of book titles and details. High‐resolution digital imaging complemented analytical data. Results of the technical examination revealed the material composition and the development of the painting, contributing to shed new light on the production of the portrait, the history and significance of the portrait.

A multimodal scanner coupling XRF, UV–Vis–NIR photoluminescence and Vis–NIR–SWIR reflectance imaging spectroscopy for cultural heritage studies

AbstractScanning x‐ray fluorescence (MA‐XRF), Reflectance Imaging Spectroscopy (RIS) and Luminescence Imaging Spectroscopy (LIS) are scientific methods extensively used in the investigation of artworks in Cultural Heritage Science. Nevertheless, these three highly complementary imaging methods have never been implemented in a single instrument. In this paper, we present a scanning system that is the first to simultaneously combine MA‐XRF, RIS, and LIS techniques, generating spatially aligned hyperspectral datasets. The specifications of the instrument and of the collected datacubes are described, together with the processing pipeline developed for the coupled exploitation and interpretation. The operation of this instrument, combining XRF with RIS and LIS mapping in an extended range (400–2500 nm and 200–1000 nm, respectively), is exemplified on an anonymous test painting, studied previously. A focus on a restored area of this painting allows to illustrates the complementarity of the three aforementioned methods, for the visualization and characterization of pigments, varnish, and binders.

Novel integration of non-invasive imaging techniques for the analysis of an egg tempera painting by Pietro Lorenzetti

The identification of an artist's palette through the application of non-invasive techniques is a challenging goal due to the huge variety of artistic materials that constitutes a painting. An effective approach is to combine several techniques providing complementary information in order to minimise the risk of misinterpreting the data. In this paper, we propose a multi-analytical method comprising three non-invasive mapping techniques, namely Reflectance Imaging Spectroscopy (RIS), Macro-X-Ray Fluorescence (MA-XRF) and Fluorescence Lifetime Imaging (FLI), for the study of a fourteenth-century painting by Pietro Lorenzetti from the Uffizi Gallery collection. For the low-cost and time-saving interpretation and integration of the data provided by the different techniques, a purposely developed software for multivariate statistical analysis was used. FLI data were acquired with a prototype applied for the first time on a work of art, and the data were processed with a method based on phasor analysis. The information obtained was discussed within a multidisciplinary team of experts on painting materials and data processing belonging to both the scientific and the conservation community.

Logistic splicing correction for VNIR-SWIR reflectance imaging spectroscopy.

In the field of spectroscopy, a splicing correction is a process by which two spectra captured with different sensors in adjacent or overlapping electromagnetic spectrum ranges are smoothly connected. In our study, we extend this concept to the case of reflectance imaging spectroscopy in the visible-near-infrared (VNIR) and short-wave infrared (SWIR), accounting for additional sources of noise that arise at the pixel level. The proposed approach exploits the adaptive fitting of a logistic function to compute correcting coefficients that harmonize the two spectral sets. This short Letter addresses usage conditions and compares results against the existing state of the art.

Multiscale characterization of shellfish purple and other organic colorants in 20th-century traditional enredos from Oaxaca, Mexico

Enredos are iconic textiles that have been produced for centuries by Mexican communities to celebrate pregnancy, weddings, etc. They have been traditionally dyed with three natural dyes, namely indigo, cochineal, and shellfish purple. In this study two modern enredos produced in the 1980s, now in the collection of the National Museum of Mexican Art, were investigated with the aim of understanding the colorants used and informing on the use of traditional dyeing practices in modern Oaxaca.The results were obtained by a combination of non-invasive analytical techniques, namely reflectance imaging spectroscopy (RIS) and macro X-ray fluorescence (MA-XRF), and high pressure liquid chromatography coupled to diode array detector and tandem mass spectrometry (HPLC-DAD-MS/MS). In addition to representing the first example of this combination of techniques applied to the study of textiles, this study also reports on the first characterization of the purple dye extracted from the Plicopurpura pansa G. mollusk by HPLC-DAD-MS/MS. Moreover, this study reveals the simultaneous use of synthetic red dyes with naturally-derived colorants such as indigo and shellfish purple. The limitations of the various techniques to provide an ultimate identification of certain dyes are emphasized together with the need for additional foundational research to expand molecular databases for the identification of synthetic dyes. Nevertheless, the results shed light on a dynamic dyeing scenario in modern Oaxaca (Mexico), in which traditional materials and methods are used alongside new ones in an attempt to preserve meaningful local practices.

A multi-analytical study of the palette of impressionist and post-impressionist Puerto Rican artists

This paper presents the pigment characterization in six impressionist and post-impressionist paintings by three leading Puerto Rican artists: Francisco Oller (1833–1917), José Cuchí y Arnau (1857–1925), and Ramón Frade (1875–1954). The paintings, belonging to the Corporación de las Artes Musicales and Museo de Arte de Puerto Rico (San Juan, Puerto Rico), were investigated through a combination of complementary non- and micro-invasive scientific techniques. The use of non-invasive macro-X-ray fluorescence (MA-XRF) and reflectance imaging spectroscopy (RIS) was applied for the first time to characterize Puerto Rican artists’ palette. The non-invasive approach was integrated with spectroscopic techniques such as Raman and/or Fourier-transform infrared (FTIR) spectroscopy, as well as high pressure liquid chromatography coupled to diode array detector and tandem mass spectrometry (HPLC-DAD-MS/MS), when sampling was possible. While this technical investigation reveals pigments that are typical for late 19th/early twentieth century paintings, it also emphasizes some unexpected findings, including the use of cobalt green and synthetic yellow lakes, which enabled the date given to some of the paintings to be refined to post 1910 rather than their current dates of ca. 1890. This study confirms that the Puerto Rican artist’s palettes are very similar to their European contemporaries, underscoring both their European training and their attempt to adapt these methods of painting to a new Caribbean identity emerging from the Spanish American War.

Identification and mapping of ancient pigments in a Roman Egyptian funerary portrait by application of reflectance and luminescence imaging spectroscopy

Imaging spectroscopy (IS) is an important tool in the comprehensive technical analysis required of archaeological paintings. The complexity of pigment mixtures, diverse artistic practices and painting technologies, and the often-fragile and weathered nature of these objects render macroscale, non-invasive chemical mapping an essential component of the analytical protocol. Furthermore, the use of pigments such as Egyptian blue and madder lake, featuring diagnostic photoluminescence emission, provides motivation to perform photoluminescence mapping on the macroscale. This work demonstrates and advances new applications of dual-mode imaging spectroscopy and data analysis approaches for ancient painting. Both reflectance (RIS) and luminescence (LIS) modes were utilized for the study of a Roman Egyptian funerary portrait from second century CE Egypt. The first derivative of the RIS image cube was analyzed and found to significantly improve materials separation, identification, and the extent of mapping. Egyptian blue and madder lake were mapped across a decorated surface using their luminescence spectral signatures in the region of 540–1000 nm as endmembers in LIS analyses. Linear unmixing of the LIS endmembers and subsequent derivative analyses resulted in an improved separation and mapping of the luminescence pigments. RIS and LIS studies, combined with complementary, single-spot collection elemental and molecular spectroscopy, were able to successfully characterize the portrait’s painting materials and binding media used by the ancient artist, providing key insight into their material use, stylistic practices, and technological choices.

Reflectance Imaging Spectroscopy (RIS) for Operation Night Watch: Challenges and Achievements of Imaging Rembrandt's Masterpiece in the Glass Chamber at the Rijksmuseum.

Visible and infrared reflectance imaging spectroscopy is one of the several non-invasive techniques used during Operation Night Watch for the study of Rembrandt’s iconic masterpiece The Night Watch (1642). The goals of this project include the identification and mapping of the artists’ materials, providing information about the painting technique used as well as documenting the painting’s current state and ultimately determining the possible conservation plan. The large size of the painting (3.78 m by 4.53 m) and the diversity of the technical investigations being performed make Operation Night Watch the largest research project ever undertaken at the Rijksmuseum. To construct a complete reflectance image cube at a high spatial resolution (168 µm2) and spectral resolution (2.54 to 6 nm), the painting was imaged with two high-sensitivity line scanning hyperspectral cameras (VNIR 400 to 1000 nm, 2.54 nm, and SWIR 900 to 2500 nm, 6 nm). Given the large size of the painting, a custom computer-controlled 3-D imaging frame was constructed to move each camera, along with lights, across the painting surface. A third axis, normal to the painting, was added along with a distance-sensing system which kept the cameras in focus during the scanning. A total of 200 hyperspectral image swaths were collected, mosaicked and registered to a high-resolution color image to sub-pixel accuracy using a novel registration algorithm. The preliminary analysis of the VNIR and SWIR reflectance images has identified many of the pigments used and their distribution across the painting. The SWIR, in particular, has provided an improved visualization of the preparatory sketches and changes in the painted composition. These data sets, when combined with the results from the other spectral imaging modalities and paint sample analyses, will provide the most complete understanding of the materials and painting techniques used by Rembrandt in The Night Watch.

Micro reflectance imaging spectroscopy for pigment identification in painting cross sections

Micro reflectance imaging spectroscopy for pigment identification in painting cross sections

Imaging spectroscopies to characterize a 13th century Japanese handscroll, The Miraculous Interventions of Jiz\u014d Bosatsu

Scientific imaging of a large fragile work of art can be especially challenging, but especially rewarding to better grasp the complexity and changes that have occurred during its creation and lifetime. Here, noninvasive imaging, macro X-ray fluorescence (MAXRF) imaging spectroscopy and reflectance imaging spectroscopy, from the visible to the near infrared spectral range, are utilized to document a 14-m-long Japanese narrative handscroll, The Miraculous Interventions of Jizō Bosatsu. Due to the scroll’s age and its handling during past use as a teaching tool, it has a number of conservation needs and shows evidence of past repairs. The scroll has extensive and severe creasing, breaks and tears, as well as unstable and powdering pigments. Microscopic observation and scientific analyses were performed both to document the current condition of the scroll and to better understand its long history. Combining RIS and MAXRF allowed for pigment characterization through elemental and molecular information. While RIS and MAXRF previously have been applied to the study of other painted materials, their application to East Asian paintings is rare. The obstacles of the scroll’s length and fragile uneven surface were overcome by optimizing the setups of the two imaging systems. The MAXRF and RIS analyses, here focused on a select scene of the scroll, found certain original pigments common in early Japanese scroll paintings were used frequently, such as vermilion, iron-based compounds (yellow and red ochres), and copper-containing greens, while others occurred sparingly, such as azurite and red lead. A chloride-containing lead-based white pigment was employed. Faded organic colorants, notably indigo as well as an organic yellow/brown, could be detected but their vibrancy has been muted over the centuries. In the case of indigo, it may be visibly observed in some areas; however, analysis revealed its previously unknown presence mixed with a copper green in a select area. This focused study sets a foundation for further studies on both this object and other Asian works of art.

Synchronized Hardware-Registered VIS-NIR Imaging Spectroscopy and 3D Sensing on a Fresco by Botticelli.

We discuss a synchronised sensing technique for the analysis of painted surfaces of frescos. Specifically, the performance of Visible-Near Infrared (VIS-NIR) Reflectance Imaging Spectroscopy (RIS) synchronized with three-dimensional (3D) acquisition is demonstrated in the study of a detached mural painting by Alessandro Botticelli. Synchronized sensing generates georeferenced data for simplified data treatment and interpretation. We show how such output data can provide key information to interpret important fresco surface and subsurface features (e.g., painting technique, material composition, pentimenti).

Origin of the degassing pipes at the Ries impact structure and implications for impact‐induced alteration on Mars and other planetary bodies

AbstractThe impact melt‐bearing breccias at the Ries impact structure, Germany, host degassing pipes: vertical structures that are inferred to represent conduits along which gases and fluids escaped to the surface, consistent with hydrothermal activity that occurs soon after an impact event. Although the presence of degassing pipes has been recognized within the well‐preserved and long‐studied ejecta deposits at the Ries, a detailed mineralogical study of their alteration mineralogy, as an avenue to elucidate their origins, has not been conducted to date. Through the application of high‐resolution in situ reflectance imaging spectroscopy and X‐ray diffraction, this study shows for the first time that the degassing pipe interiors and associated alteration are comprised of hydrated and hydroxylated silicates (i.e., Fe/Mg smectitic clay minerals with chloritic or other hydroxy‐interlayered material) as secondary hydrothermal mineral phases. This study spatially extends the known effects of impact hydrothermal activity into the ejecta deposits, beyond the crater rim. It has been suggested that the degassing pipes at the Ries are analogous to crater‐related pit clusters observed in impact melt‐bearing deposits on Mars, Ceres, and Vesta. The results of this work may inform on the presence of crustal volatiles and their interaction during the impact process on rocky bodies throughout the solar system. The Mars 2020 Perseverance rover may have the opportunity to investigate impact‐related features in situ; if so, this work suggests that such investigations may provide key information on the origin and formation of clay minerals on Mars as well as hold exciting implications for future Mars exploration.

A Preliminary Study on the Differentiation of Linseed and Poppy Oil Using Principal Component Analysis Methods Applied to Fiber Optics Reflectance Spectroscopy and Diffuse Reflectance Imaging Spectroscopy.

This paper presents results from the examination of a set of experimental samples using fibre optic reflectance spectroscopy (FORS) and diffuse reflectance imaging spectroscopy in the short-wave infrared (SWIR) range, combined with statistical analysis of the data for the discrimination and mapping of poppy and linseed oil. The aim was to evaluate the efficacy of this non-invasive approach for the study of paint samples with a view to the application of the method for characterisation of the two drying oils in painted art. The approach allowed discrimination between the two drying oils based on FORS spectra and the hyperspectral cube, indicating the influence of the spectral region around 1700 nm on the statistical discrimination based on the anti-symmetric and symmetric first overtone stretching of methylenic CH2 groups. This method is being studied as a potential non-invasive method of organic analysis of oil types that have formerly been studied using gas chromatography-mass spectrometry (GC-MS), which requires micro-samples.